IO¶

Usage

use IO;

or

import IO;

Submodules

FormattedIO

Support for a variety of kinds of input and output.

Note

All Chapel programs automatically include write, writeln and writef.

Input/output (I/O) facilities in Chapel include the types file and channel; the constants stdin, stdout and stderr; the functions open, file.close, file.reader, file.writer, channel.read, channel.write, and many others.

Warning

Please be aware, the IO Module documentation is under development and currently contains some minor inconsistencies.

For example, the channel type has been replaced with the fileWriter and fileReader types; however, not all references to channel have been removed from the docs. As such, note that writing methods on the channel type (such as channel.writeln) are intended to be called on a fileWriter and reading methods are intended to be called on a fileReader.

I/O Overview¶

A file in Chapel identifies a file in the underlying operating system. Reads and writes to a file are done via one or more channels associated with the file. Each channel uses a buffer to provide sequential read or write access to its file, optionally starting at an offset.

For example, the following program opens a file and writes an integer to it:

// open the file "test-file.txt" for writing, creating it if
// it does not exist yet.
var myFile = open("test-file.txt", iomode.cw);

// create a writing channel starting at file offset 0
// (start and end offsets can be specified when creating the
// channel)
var myWritingChannel = myFile.writer();

var x: int = 17;

// This function will write the human-readable text version of x;
// binary I/O is also possible.
myWritingChannel.write(x);

// Now test-file.txt contains:
// 17

Then, the following program can be used to read the integer:

// open the file "test-file.txt" for reading only
var myFile = open("test-file.txt", iomode.r);

// create a reading channel starting at file offset 0
// (start and end offsets can be specified when creating the
// channel)
var myReadingChannel = myFile.reader();

var x: int;

// Now read a textual integer. Note that the
// channel.read function returns a bool to indicate
// if it read something or if the end of the file
// was reached before something could be read.
var readSomething = myReadingChannel.read(x);

writeln("Read integer ", x);
// prints out:
// 17

The read functions allow one to read values into variables as the following example demonstrates. It shows three ways to read values into a pair of variables x and y.

var x: int;
var y: real;
/* reading into variable expressions, returning
   true if the values were read, false on EOF */
var ok:bool = read(x, y);

/* reading via a single type argument */
x = read(int);
y = read(real);

/* reading via multiple type arguments */
(x, y) = read(int, real);

Design Rationale¶

Since channels operate independently, concurrent I/O to the same open file is possible without contending for locks. Furthermore, since the channel (and not the file) stores the current file offset, it is straightforward to create programs that access the same open file in parallel. Note that such parallel access is not possible in C when multiple threads are using the same FILE* to write to different regions of a file because of the race condition between fseek and fwrite. Because of these issues, Chapel programmers wishing to perform I/O will need to know how to open files as well as create channels.

I/O Styles¶

Warning

iostyle is now unstable. We are working on creating a full-featured replacement for it but in the meantime the Formatted I/O facilities are still available to control formatting.

Reading and writing of Chapel’s basic types is regulated by an applicable iostyle. In particular, the I/O style controls whether binary or text I/O should be performed. For binary I/O it specifies, for example, byte order and string encoding. For text I/O it specifies string representation; the base, field width and precision for numeric types; and so on. Each channel has an associated I/O style. It applies to all read/write operations on that channel, except when the program specifies explicitly an I/O style for a particular read or write.

See the definition for the iostyle type. This type represents I/O styles and provides details on formatting and other representation choices.

The default value of the iostyle type is undefined. However, the compiler-generated constructor is available. It can be used to generate the default I/O style, with or without modifications. In addition, the function defaultIOStyle will return the default I/O style just as new iostyle() will.

The I/O style for an I/O operation can be provided through an optional style= argument in a variety of places:

when performing the I/O, e.g. in calls to channel.write or channel.read

when creating the channel with file.reader or file.writer

or when creating the file with e.g. open

Note that file.reader, or file.writer will copy the file’s I/O style if a style= argument is not provided. Also note that I/O functions on channels will by default use the I/O style stored with that channel.

A channel’s I/O style may be retrieved using channel._style and set using channel._set_style. These functions should only be called while the channel lock is held, however. See Synchronization of Channel Data and Avoiding Data Races for more information on channel locks.

As an example for specifying an I/O style, the code below specifies the minimum width for writing numbers so array elements are aligned in the output:

stdout.writeln(MyArray, new iostyle(min_width=10));

I/O facilities in Chapel also include several other ways to control I/O formatting. There is support for formatted I/O with FormattedIO.channel.readf and FormattedIO.channel.writef. Also note that record or class implementations can provide custom functions implementing read or write operations for that type (see The readThis() and writeThis() Methods).

Files¶

There are several functions that open a file and return a file including open, openTempFile, openmem, openfd, and openfp.

Once a file is open, it is necessary to create associated channel(s) - see file.reader and file.writer - to write to and/or read from the file.

Use the file.fsync function to explicitly synchronize the file to ensure that file data is committed to the file’s underlying device for persistence.

To release any resources associated with a file, it is necessary to first close any channels using that file (with channel.close) and then the file itself (with file.close).

Note

Escaped strings can be used for paths on systems where UTF-8 file names are not enforced.

Functions for Channel Creation¶

file.writer creates a channel for writing to a file, and file.reader create a channel for reading from a file.

Synchronization of Channel Data and Avoiding Data Races¶

Channels (and files) contain locks in order to keep their operation safe for multiple tasks. When creating a channel, it is possible to disable the lock (for performance reasons) by passing locking=false to e.g. file.writer(). Some channel methods - in particular those beginning with the underscore - should only be called on locked channels. With these methods, it is possible to get or set the channel style, or perform I/O “transactions” (see channel.mark and channel._mark). To use these methods, first lock the channel with channel.lock, call the methods you need, then unlock the channel with channel.unlock. Note that in the future, we may move to alternative ways of calling these functions that guarantee that they are not called on a channel without the appropriate locking.

Besides data races that can occur if locking is not used in channels when it should be, it is also possible for there to be data races on file data that is buffered simultaneously in multiple channels. The main way to avoid such data races is the channel.flush synchronization operation. channel.flush will make all writes to the channel, if any, available to concurrent viewers of its associated file, such as other channels or other applications accessing this file concurrently. See the note below for more details on the situation in which this kind of data race can occur.

Note

Since channels can buffer data until channel.flush is called, it is possible to write programs that have undefined behaviour because of race conditions on channel buffers. In particular, the problem comes up for programs that make:

concurrent operations on multiple channels that operate on overlapping regions of a file

where at least one of the overlapping channels is a writing channel

and where data could be stored in more than one of the overlapping channel’s buffers at the same time (i.e., write and read ordering are not enforced through channel.flush and other means such as sync variables).

Note that it is possible in some cases to create a file that does not allow multiple channels at different offsets. Channels created on such files will not change the file’s position based on a start= offset arguments. Instead, each read or write operation will use the file descriptor’s current position. Therefore, only one channel should be created for files created in the following situations:

with openfp

with openfd when provided a non-seekable system file descriptor

Performing I/O with Channels¶

Channels contain read and write methods, which are generic methods that can read or write anything, and can also take optional arguments such as I/O style or. These functions generally take any number of arguments and throw if there was an error. See:

channel.write

channel.writeln

channel.writebits

FormattedIO.channel.writef (see also Formatted I/O)

channel.read

channel.readln

channel.readbits

FormattedIO.channel.readf (see also Formatted I/O)

Sometimes it’s important to flush the buffer in a channel - to do that, use the channel.flush() method. Flushing the buffer will make all writes available to other applications or other views of the file (e.g., it will call the OS call pwrite()). It is also possible to close a channel, which will implicitly flush it and release any buffer memory used by the channel. Note that if you need to ensure that data from a channel is on disk, you’ll have to call channel.flush or channel.close and then file.fsync on the related file.

Functions for Closing Channels¶

A channel must be closed in order to free the resources allocated for it, to ensure that data written to it is visible to other channels, or to allow the associated file to be closed.

See channel.close.

It is an error to perform any I/O operations on a channel that has been closed. It is an error to close a file when it has channels that have not been closed.

Files and channels are reference counted. Each file and channel is closed automatically when no references to it remain. For example, if a local variable is the only reference to a channel, the channel will be closed when that variable goes out of scope. Programs may also close a file or channel explicitly.

The `stdin`, `stdout`, and `stderr` Channels¶

Chapel provides the predefined channels stdin, stdout, and stderr to access the corresponding operating system streams standard input, standard output, and standard error.

stdin supports reading; stdout and stderr support writing.

All three channels are safe to use concurrently. Their types’ kind argument is dynamic.

Error Handling¶

Most I/O routines throw a OS.SystemError, and can be handled appropriately with try and catch.

Some of these subclasses commonly used within the I/O implementation include:

OS.EofError - the end of file was reached

OS.UnexpectedEofError - a read or write only returned part of the requested data

OS.BadFormatError - data read did not adhere to the requested format

OS.InsufficientCapacityError - a read or write operation required more storage than was available

An error code can be converted to a string using the function OS.errorToString().

Ensuring Successful I/O¶

It is possible - in some situations - for I/O to fail without returning an error. In cases where a programmer wants to be sure that there was no error writing the data to disk, it is important to call file.fsync to make sure that data has arrived on disk without an error. Many errors can be reported with a typical operation, but some errors can only be reported by the system during file.close or even file.fsync.

When a file (or channel) is closed, data written to that file will be written to disk eventually by the operating system. If an application needs to be sure that the data is immediately written to persistent storage, it should use file.fsync prior to closing the file.

Correspondence with C I/O¶

It is not possible to seek, read, or write to a file directly; channels must be created and used.

channel.flush in Chapel has the same conceptual meaning as fflush() in C. However, fflush() is not necessarily called in channel.flush(), unlike fsync(), which is actually called by file.fsync() in Chapel.

IO Functions and Types¶

enum iomode { r = 1, cw = 2, rw = 3, cwr = 4 }¶

The iomode type is an enum. When used as arguments when opening files, its constants have the same meaning as the following strings passed to fopen() in C:

`iomode`	`fopen()` argument	Description
`iomode.r`	`"r"`	open an existing file for reading.
`iomode.rw`	`"r+"`	open an existing file for reading and writing.
`iomode.cw`	`"w"`	create a new file for writing. If the file already exists, its contents are truncated.
`iomode.cwr`	`"w+"`	same as `iomode.cw`, but reading from the file is also allowed.

However, open() in Chapel does not necessarily invoke fopen() in C.

enum iokind { dynamic = 0, native = 1, big = 2, little = 3 }¶

The iokind type is an enum. When used as arguments to the channel type, its constants have the following meaning:

iokind.dynamic means that the applicable I/O style has full effect and as a result the kind varies at runtime.
iokind.native means binary I/O in native byte order (similar to iokind.big but with the byte order that is native to the target platform).
iokind.big means binary I/O with big-endian byte order is performed when writing/reading basic types from the channel.
iokind.little means binary I/O with little-endian byte order (similar to iokind.big but with little-endian byte order).

In the case of iokind.big, iokind.little, and iokind.native the applicable iostyle is consulted when writing/reading strings, but not for other basic types.

There are synonyms available for these values:

iodynamic = iokind.dynamic
ionative = iokind.native
iobig = iokind.big
iolittle = iokind.little

param iodynamic = iokind.dynamic¶: A synonym for iokind.dynamic; see iokind

param ionative = iokind.native¶: A synonym for iokind.native; see iokind

param iobig = iokind.big¶: A synonym for iokind.big; see iokind

param iolittle = iokind.little¶: A synonym for iokind.little; see iokind

enum ioendian { native = 0, big = 1, little = 2 }¶

The ioendian type is an enum. When used as an argument to the channel methods, its constants have the following meanings:

ioendian.big means binary I/O is performed in big-endian byte order.
ioendian.little means binary I/O is performed in little-endian byte order.
ioendian.native means binary I/O is performed in the byte order that is native to the target platform.

enum iostringstyle { len1b_data = -1, len2b_data = -2, len4b_data = -4, len8b_data = -8, lenVb_data = -10, data_toeof = -0xff00, data_null = -0x0100 }¶

This enum contains values used to control binary I/O with strings via the str_style field in iostyle.

iostringstyle.len1b_data indicates a string format of 1 byte of length followed by length bytes of string data.
iostringstyle.len2b_data indicates a string format of 2 bytes of length followed by length bytes of string data.
iostringstyle.len4b_data indicates a string format of 4 bytes of length followed by length bytes of string data.
iostringstyle.len8b_data indicates a string format of 8 bytes of length followed by length bytes of string data.
iostringstyle.lenVb_data indicates a string format of a variable number of bytes of length, encoded with high-bit meaning more bytes of length follow, and where the 7-bits of length from each byte store the 7-bit portions of the length in order from least-significant to most-significant. This way of encoding a variable-byte length matches Google Protocol Buffers.
iostringstyle.data_toeof indicates a string format that contains only the string data without any length or terminator. When reading, this format will read a string until the end of the file is reached.
iostringstyle.data_null indicates a string that is terminated by a zero byte. It can be combined with other numeric values to indicate a string terminated by a particular byte. For example, to indicate a string terminated by $ (which in ASCII has byte value 0x24), one would use the value iostringstyle.data_null|0x24.
A positive and nonzero value indicates that a string of exactly that many bytes should be read or written.

Warning

iostringstyle is unstable and will eventually be replaced

enum iostringformat { word = 0, basic = 1, chpl = 2, json = 3, toend = 4, toeof = 5 }¶

This enum contains values used to control text I/O with strings via the string_format field in iostyle.

iostringformat.word means string is as-is; reading reads until whitespace. This is the default.

iostringformat.basic means only escape string_end and \ with \

iostringformat.chpl means escape string_end \ ' " \n with \ and nonprinting characters c = 0xXY with \xXY

iostringformat.json means escape string_end " and \ with \, and nonprinting characters c = \uABCD

iostringformat.toend means string is as-is; reading reads until string_end

iostringformat.toeof means string is as-is; reading reads until end of file

Warning

iostringformat is unstable and will eventually be replaced

proc stringStyleTerminated(terminator: uint(8))¶

This method returns the appropriate iostyle str_style value to indicate a string format where strings are terminated by a particular byte.

Arguments: terminator – a byte value that the strings will be terminated by
Returns: a value that indicates a string format where strings are terminated by the terminator byte. This value is appropriate to store in iostyle.str_style.

Warning

stringStyleTerminated is unstable because it supports the unstable type ‘iostyle’

proc stringStyleNullTerminated()¶: This method returns the appropriate iostyle str_style value to indicate a string format where strings are terminated by a zero byte.

Warning

stringStyleNullTerminated is unstable because it supports the unstable type ‘iostyle’

proc stringStyleWithLength(lengthBytes: int) throws¶

Return the appropriate iostyle str_style value to indicate a string format where string data is preceded by a lengthBytes of length. Only lengths of 1, 2, 4, or 8 are supported. When lengthBytes is 0, the returned value indicates variable-byte length.

Throws: SystemError – Thrown for an unsupported value of lengthBytes.

Warning

stringStyleWithLength is unstable because it supports the unstable type ‘iostyle’

type iostyle = iostyleInternal¶: Warning

iostyle is unstable, a new way of controlling channel output is planned

proc defaultIOStyle(): iostyle¶

Returns: the default I/O style. See iostyle and I/O Styles

Warning

defaultIOStyle is unstable due to returning an unstable type

record ioHintSet¶

A value of the ioHintSet type defines a set of hints about the I/O that the file or channel will perform. These hints may be used by the implementation to select optimized versions of the I/O operations.

Most hints have POSIX equivalents associated with posix_fadvise() and posix_madvise().

use IO;

// define a set of hints using a union operation
var hints = ioHintSet::sequential | ioHintSet::prefetch;

// open a file using the hints
var f: file;
try! {
  f = open("path/to/my/file.txt", iomode.r, hints=hints);
}

proc type empty¶: Defines an empty set, which provides no hints. Corresponds to ‘POSIX_*_NORMAL’.

proc type sequential¶: Suggests that the file will be accessed sequentially. Corresponds to ‘POSIX_*_SEQUENTIAL’

proc type random¶: Suggests that the file will be accessed randomly. Corresponds to ‘POSIX_*_RANDOM’.

proc type prefetch¶: Suggests that the runtime/OS should immediately begin prefetching the file contents. Corresponds to ‘POSIX_*_WILLNEED’.

proc type mmap¶: Suggests that ‘mmap’ should be used to access the file contents

proc type noMmap¶: Suggests that ‘mmap’ should not be used to access the file contents. Instead, pread/pwrite are used.

operator ioHintSet.|(lhs: ioHintSet, rhs: ioHintSet): Compute the union of two ioHintSets

operator ioHintSet.&(lhs: ioHintSet, rhs: ioHintSet): Compute the intersection of two ioHintSets

operator ioHintSet.==(lhs: ioHintSet, rhs: ioHintSet)¶: Compare two ioHintSets for equality

operator ioHintSet.!=(lhs: ioHintSet, rhs: ioHintSet)¶: Compare two ioHintSets for inequality

record file¶

The file type is implementation-defined. A value of the file type refers to the state that is used by the implementation to identify and interact with the OS file.

When a file formal argument has default intent, the actual is passed by const ref to the formal upon a function call, and the formal cannot be assigned within the function.

The default value of the file type does not represent any OS file. It is illegal to perform any I/O operations on the default value.

proc file.check() throws¶

Throw an error if this is not a valid representation of an OS file.

Throws: SystemError – Indicates that this does not represent an OS file.

proc file.close() throws¶

Close a file.

In order to free the resources allocated for a file, it must be closed using this method.

Closing a file does not guarantee immediate persistence of the performed updates, if any. In cases where immediate persistence is important, file.fsync should be used for that purpose prior to closing the file. In particular, even though closing the file might complete without errors, the data written might not persist in the event of a severe error like running out of storage space or power loss. See also Ensuring Successful I/O.

Files are automatically closed when the file variable goes out of scope and all channels using that file are closed. Programs may also explicitly close a file using this method.

It is an error to perform any I/O operations on a file that has been closed. It is an error to close a file when it has channels that have not been closed.

Throws: SystemError – Thrown if the file could not be closed.

proc file.fsync() throws¶

Sync a file to disk.

Commits file data to the device associated with this file. Data written to the file by a channel will only be guaranteed committed if the channel has been closed or flushed.

This function will typically call the fsync system call.

Throws: SystemError – Thrown if the file could not be synced.

config param filePathAbsolute = false¶

A compile-time parameter to control the behavior of file.path

When ‘false’, the deprecated behavior is used (i.e., return the shortest of the relative path and the absolute path)

When ‘true’, the new behavior is used (i.e., always return the absolute path)

proc file.path: string throws¶: Warning

The variant of file.path that can return a relative path is deprecated; please compile with -sfilePathAbsolute=true to use the strictly absolute variant

proc file.path: string throws

Get the absolute path to an open file.

Note that not all files have a path (e.g. files opened with openmem), and that this function may not work on all operating systems.

The function Path.realPath is an alternative way to get the path to a file.

Returns: the absolute path to the file
Return type: string
Throws: SystemError – Thrown if the path could not be retrieved.

proc file.size: int throws¶

Get the current size of an open file. Note that the size can always change if other channels, tasks or programs are writing to the file.

Returns: the current file size
Throws: SystemError – Thrown if the size could not be retrieved.

proc open(path: string, mode: iomode, hints = ioHintSet.empty, style: iostyle): file throws¶: Warning

open with a style argument is unstable

proc open(path: string, mode: iomode, hints = ioHintSet.empty): file throws

Open a file on a filesystem. Note that once the file is open, you will need to use a file.reader or file.writer to create a channel to actually perform I/O operations

Arguments

path – which file to open (for example, “some/file.txt”).
mode – specify whether to open the file for reading or writing and whether or not to create the file if it doesn’t exist. See iomode.
hints – optional argument to specify any hints to the I/O system about this file. See ioHintSet.

Returns

an open file to the requested resource.

Throws

FileNotFoundError – Thrown if part of the provided path did not exist
PermissionError – Thrown if part of the provided path had inappropriate permissions
NotADirectoryError – Thrown if part of the provided path was expected to be a directory but was not
SystemError – Thrown if the file could not be opened.

proc openfd(fd: c_int, hints = ioHintSet.empty, style: iostyle): file throws¶: Warning

openfd with a style argument is unstable

proc openfd(fd: c_int, hints = ioHintSet.empty): file throws

Create a Chapel file that works with a system file descriptor. Note that once the file is open, you will need to use a file.reader or file.writer to create a channel to actually perform I/O operations

The system file descriptor will be closed when the Chapel file is closed.

Note

This function can be used to create Chapel files that refer to system file descriptors that do not support the seek functionality. For example, file descriptors that represent pipes or open socket connections have this property. In that case, the resulting file value should only be used with one channel at a time. The I/O system will ignore the channel offsets when reading or writing to files backed by non-seekable file descriptors.

Arguments

fd – a system file descriptor.
hints – optional argument to specify any hints to the I/O system about this file. See ioHintSet.

Returns

an open file using the specified file descriptor.

Throws

SystemError – Thrown if the file descriptor could not be retrieved.

proc openfp(fp: c_FILE, hints = ioHintSet.empty, style: iostyle): file throws¶: Warning

openfp with a style argument is unstable

proc openfp(fp: c_FILE, hints = ioHintSet.empty): file throws

Create a Chapel file that wraps around an open C file. A pointer to a C FILE object can be obtained via Chapel’s C Interoperability functionality.

Once the Chapel file is created, you will need to use a file.reader or file.writer to create a channel to perform I/O operations on the C file.

Note

The resulting file value should only be used with one channel at a time. The I/O system will ignore the channel offsets when reading or writing to a file opened with openfp.

Arguments

fp – a pointer to a C FILE. See c_FILE.
hints – optional argument to specify any hints to the I/O system about this file. See ioHintSet.

Returns

an open file corresponding to the C file.

Throws

SystemError – Thrown if the C file could not be retrieved.

proc openfp(fp: _file, hints = ioHintSet.empty): file throws: Warning

‘_file’ is deprecated; use the variant of ‘openfp’ that takes a ‘c_FILE’ instead

proc openTempFile(hints = ioHintSet.empty, style: iostyle): file throws¶: Warning

openTempFile with a style argument is unstable

proc opentmp(hints = ioHintSet.empty, style: iostyle): file throws¶: Warning

opentmp is deprecated, please use openTempFile instead

proc openTempFile(hints = ioHintSet.empty): file throws

Open a temporary file. Note that once the file is open, you will need to use a file.reader or file.writer to create a channel to actually perform I/O operations.

The temporary file will be created in an OS-dependent temporary directory, for example “/tmp” is the typical location. The temporary file will be deleted upon closing.

Temporary files are opened with iomode iomode.cwr; that is, a new file is created that supports both writing and reading. When possible, it may be opened using OS support for temporary files in order to make sure that a new file is created only for use by the current application.

Arguments: hints – optional argument to specify any hints to the I/O system about this file. See ioHintSet.
Returns: an open temporary file.
Throws: SystemError – Thrown if the temporary file could not be opened.

proc opentmp(hints = ioHintSet.empty): file throws: Warning

opentmp is deprecated, please use openTempFile instead

proc openmem(style: iostyle): file throws¶: Warning

openmem with a style argument is unstable

proc openmem(): file throws

Open a file that is backed by a buffer in memory that will not persist when the file is closed. Note that once the file is open, you will need to use a file.reader or file.writer to create a channel to actually perform I/O operations.

The resulting file supports both reading and writing.

Returns: an open memory file.
Throws: SystemError – Thrown if the memory buffered file could not be opened.

type fileReader¶

A fileReader supports sequential reading from an underlying file object. It can buffer data. Read operations on it might return old data. Use channel.flush to control this buffering.

The fileReader type is implementation-defined. A value of the fileReader type refers to the state that is used to implement the reading operations.

When a fileReader formal argument has default intent, the actual is passed by const ref to the formal upon a function call, and the formal cannot be assigned within the function.

The default value of the fileReader type is not associated with any file, and so cannot be used to perform I/O.

The fileReader type is generic.

The fileReader type supports 3 fields:

param writing: bool which is always false for fileReader

param kind:iokind: kind is an enum iokind that allows narrowing this channel’s I/O style for more efficient binary I/O.

param locking:bool: locking is a boolean indicating whether it is safe to use this channel concurrently (when true).

type fileWriter¶

A fileWriter supports sequential writing to an underlying file object. A fileWriter can buffer data. Write operations might not have an immediate effect. Use channel.flush to control this buffering.

The fileWriter type is implementation-defined. A value of the fileWriter type refers to the state that is used to implement the writing operations.

When a fileWriter formal argument has default intent, the actual is passed by const ref to the formal upon a function call, and the formal cannot be assigned within the function.

The default value of the fileWriter type is not associated with any file, and so cannot be used to perform I/O.

The fileWriter type is generic.

The fileWriter type supports 3 fields:

param writing: bool which is always true for fileWriter

param kind:iokind: kind is an enum iokind that allows narrowing this channel’s I/O style for more efficient binary I/O.

param locking:bool: locking is a boolean indicating whether it is safe to use this channel concurrently (when true).

type channel = _channel¶

A channel supports either sequential reading or sequential writing to an underlying file object. A channel can buffer data. Read operations on the channel might return old data. Write operations might not have an immediate effect. Use channel.flush to control this buffering.

The channel type is implementation-defined. A value of the channel type refers to the state that is used to implement the channel operations.

When a channel formal argument has default intent, the actual is passed by const ref to the formal upon a function call, and the formal cannot be assigned within the function.

The default value of the channel type is not associated with any file, and so cannot be used to perform I/O.

The channel type is generic.

The channel type supports 3 fields:

param writing: bool: writing is a boolean indicating whether the channels of this type support writing (when true) or reading (when false).

param kind:iokind: kind is an enum iokind that allows narrowing this channel’s I/O style for more efficient binary I/O.

param locking:bool: locking is a boolean indicating whether it is safe to use this channel concurrently (when true).

Note

The channel type is deprecated. Please use fileReader or fileWriter instead.

record ioChar¶

Represents a Unicode codepoint. I/O routines (such as channel.read and channel.write) can use arguments of this type in order to read or write a single Unicode codepoint.

var ch: int(32)¶: The codepoint value

record ioNewline¶

Represents a newline character or character sequence (ie \n). I/O routines (such as channel.read and channel.write) can use arguments of this type in order to read or write a newline. This is different from \n because an ioNewline always produces an actual newline, but in some cases writing \n will produce an escaped string (such as "\n").

When reading an ioNewline, read routines will skip any character sequence (including, e.g., letters and numbers) to get to the newline character unless skipWhitespaceOnly is set to true.

var skipWhitespaceOnly: bool = false¶: Normally, we will skip anything at all to get to a \n, but if skipWhitespaceOnly is set, it will be an error if we run into non-space characters other than \n.

record ioLiteral¶

Used to represent a constant string we want to read or write.

When writing, the ioLiteral is output without any quoting or escaping.

When reading, the ioLiteral must be matched exactly - or else the read call will return an error for incorrectly formatted input

var val: string¶: The value of the literal

var ignoreWhiteSpace: bool = true¶: Should read operations using this literal ignore and consume whitespace before the literal?

proc writeThis(f) throws¶

record ioBits¶

Represents a value with a particular bit length that we want to read or write. The I/O will always be done in binary mode.

var v: uint(64)¶: The bottom nbits of v will be read or written

var nbits: int(8)¶: How many of the low-order bits of v should we read or write?

proc channel.lock() throws¶

Acquire a channel’s lock.

Throws: SystemError – Thrown if the lock could not be acquired.

proc channel.unlock()¶: Release a channel’s lock.

proc channel.offset(): int(64)¶

Return the current offset of a channel.

Warning

If the channel can be used by multiple tasks, take care when doing operations that rely on the channel’s current offset. To prevent race conditions, first lock the channel with channel.lock, do the operations with channel._offset instead, then unlock it with channel.unlock.

Returns: the current offset of the channel

proc channel.advance(amount: int(64)) throws¶

Move a channel offset forward.

For a reading channel, this function will consume the next amount bytes. If EOF is reached, the channel position may be left at the EOF.

For a writing channel, this function will write amount zeros - or some other data if it is stored in the channel’s buffer, for example with channel._mark and channel._revert.

Throws: SystemError – Throws if the channel offset was not moved.

proc channel.advancePastByte(byte: uint(8)) throws¶

Reads until byte is found and then leave the channel offset just after it.

Throws

EofError – if the requested byte could not be found.
SystemError – if another error occurred.

proc channel.mark() throws¶

Mark a channel - that is, save the current offset of the channel on its mark stack. This function can only be called on a channel with locking==false.

The mark stack stores several channel offsets. For any channel offset that is between the minimum and maximum value in the mark stack, I/O operations on the channel will keep that region of the file buffered in memory so that those operations can be undone. As a result, it is possible to perform I/O transactions on a channel. The basic steps for an I/O transaction are:

mark the current position with channel.mark

do something speculative (e.g. try to read 200 bytes of anything followed by a ‘B’)

if the speculative operation was successful, commit the changes by calling channel.commit

if the speculative operation was not successful, go back to the mark by calling channel.revert. Subsequent I/O operations will work as though nothing happened.

Note

Note that it is possible to request an entire file be buffered in memory using this feature, for example by marking at offset=0 and then advancing to the end of the file. It is important to be aware of these memory space requirements.

Returns: The offset that was marked
Throws: SystemError: if marking the channel failed

proc channel.revert()¶: Abort an I/O transaction. See channel.mark. This function will pop the last element from the mark stack and then leave the previous channel offset unchanged. This function can only be called on a channel with locking==false.

proc channel.commit()¶: Commit an I/O transaction. See channel.mark. This function will pop the last element from the mark stack and then set the channel offset to the popped offset. This function can only be called on a channel with locking==false.

config param useNewSeekRegionBounds = false¶: Used to control the behavior of the region argument for channel.seek. When set to true, the region argument will fully specify the bounds of the seek. When set to false, the region argument will exclude the high bound. Defaults to false, the original behavior.

proc channel.seek(region: range(?)) throws¶

Reset a channel to point to a new part of a file. This function allows one to jump to a different part of a file without creating a new channel. It can only be called on a channel with locking==false.

The region specified must have a lower bound, but does not need to have a high bound for correctness. Specifying the high bound might be an important performance optimization since the channel will not try to read data outside of the region.

This function will, in most cases, discard the channel’s buffer. When writing, the data will be saved to the file before discarding.

Arguments: region – the new region, measured in bytes and counting from 0

Warning

The region argument will ignore any specified stride other than 1.

Throws

SystemError – if seeking failed. Possible reasons include that the file is not seekable, or that the channel is marked.
IllegalArgumentError – if region argument did not have a lower bound

proc channel.seek(region: range(?)) throws: Warning

Currently the region argument’s high bound specifies the first location in the file that is not included. This behavior is deprecated, please compile your program with -suseNewSeekRegionBounds=true to have the region argument specify the entire segment of the file covered, inclusive.

proc channel._offset(): int(64)¶: For a channel locked with channel.lock, return the offset of that channel.

proc channel._mark() throws¶

This routine is identical to channel.mark except that it can be called on channels with locking==true and should be called only once the channel has been locked with channel.lock. The channel should not be unlocked with channel.unlock until after the mark has been committed with channel._commit or reverted with channel._revert.

See channel.mark for details other than the locking discipline.

Returns: The offset that was marked
Throws: SystemError: if marking the channel failed

proc channel._revert()¶: Abort an I/O transaction. See channel._mark. This function will pop the last element from the mark stack and then leave the previous channel offset unchanged. This function should only be called on a channel that has already been locked and marked.

proc channel._commit()¶: Commit an I/O transaction. See channel._mark. This function will pop the last element from the mark stack and then set the channel offset to the popped offset. This function should only be called on a channel that has already been locked and marked.

proc channel._style(): iostyle¶: Return the current style used by a channel. This function should only be called on a locked channel.

Warning

channel._style is unstable because it returns a type that is unstable

proc channel._set_style(style: iostyle)¶: Set the style associated with a channel. This function should only be called on a locked channel.

Warning

channel._set_style is unstable because its purpose involves an unstable type

proc channel.readWriteThisFromLocale()¶: Return the locale on which an ongoing I/O was started with a channel. This method will return nilLocale unless it is called on a channel that is the formal argument to a readThis or writeThis method.

proc openreader(path: string, param kind = iokind.dynamic, param locking = true, start: int(64) = 0, end: int(64) = max(int(64)), hints = ioHintSet.empty, style: iostyle): fileReader(kind, locking) throws¶: Warning

openreader with a style argument is unstable

config param useNewOpenReaderRegionBounds = false¶: Used to control the behavior of the region argument for openreader. When set to true, the region argument will fully specify the bounds of the fileReader. When set to false, the region argument will exclude the high bound. Defaults to false, the original behavior.

proc openreader(path: string, param kind = iokind.dynamic, param locking = true, region: range(?) = 0.., hints = ioHintSet.empty): fileReader(kind, locking) throws

Open a file at a particular path and return a reading channel for it. This function is equivalent to calling open and then file.reader on the resulting file.

Arguments

path – which file to open (for example, “some/file.txt”).
kind – iokind compile-time argument to determine the corresponding parameter of the channel type. Defaults to iokind.dynamic, meaning that the associated iostyle controls the formatting choices.
locking – compile-time argument to determine whether or not the channel should use locking; sets the corresponding parameter of the channel type. Defaults to true, but when safe, setting it to false can improve performance.
region – zero-based byte offset indicating where in the file the channel should start and stop reading. Defaults to 0.., meaning from the start of the file to no specified end point.
hints – optional argument to specify any hints to the I/O system about this file. See ioHintSet.

Returns

an open reading channel to the requested resource.

Warning

The region argument will ignore any specified stride other than 1.

Throws

FileNotFoundError – Thrown if part of the provided path did not exist
PermissionError – Thrown if part of the provided path had inappropriate permissions
NotADirectoryError – Thrown if part of the provided path was expected to be a directory but was not
SystemError – Thrown if a reading channel could not be returned.
IllegalArgumentError – Thrown if trying to read explicitly prior to byte 0.

proc openreader(path: string, param kind = iokind.dynamic, param locking = true, region: range(?) = 0.., hints = ioHintSet.empty): fileReader(kind, locking) throws: Warning

Currently the region argument’s high bound specifies the first location in the file that is not included. This behavior is deprecated, please compile your program with -suseNewOpenReaderRegionBounds=true to have the region argument specify the entire segment of the file covered, inclusive.

proc openwriter(path: string, param kind = iokind.dynamic, param locking = true, start: int(64) = 0, end: int(64) = max(int(64)), hints = ioHintSet.empty, style: iostyle): fileWriter(kind, locking) throws¶: Warning

openwriter with a style argument is unstable

proc openwriter(path: string, param kind = iokind.dynamic, param locking = true, hints = ioHintSet.empty): fileWriter(kind, locking) throws

Open a file at a particular path and return a writing channel for it. This function is equivalent to calling open with iomode.cwr and then file.writer on the resulting file.

Arguments

path – which file to open (for example, “some/file.txt”).
kind – iokind compile-time argument to determine the corresponding parameter of the channel type. Defaults to iokind.dynamic, meaning that the associated iostyle controls the formatting choices.
locking – compile-time argument to determine whether or not the channel should use locking; sets the corresponding parameter of the channel type. Defaults to true, but when safe, setting it to false can improve performance.
hints – optional argument to specify any hints to the I/O system about this file. See ioHintSet.

Returns

an open writing channel to the requested resource.

Throws

FileNotFoundError – Thrown if part of the provided path did not exist
PermissionError – Thrown if part of the provided path had inappropriate permissions
NotADirectoryError – Thrown if part of the provided path was expected to be a directory but was not
SystemError – Thrown if a writing channel could not be returned.

proc file.reader(param kind = iokind.dynamic, param locking = true, start: int(64) = 0, end: int(64) = max(int(64)), hints = ioHintSet.empty, style: iostyle): fileReader(kind, locking) throws¶: Warning

reader with a style argument is unstable

config param useNewFileReaderRegionBounds = false¶: Used to control the behavior of the region argument for file.reader. When set to true, the region argument will fully specify the bounds of the fileReader. When set to false, the region argument will exclude the high bound. Defaults to false, the original behavior.

proc file.reader(param kind = iokind.dynamic, param locking = true, region: range(?) = 0.., hints = ioHintSet.empty): fileReader(kind, locking) throws

Create a fileReader that supports reading from a file. See I/O Overview.

The region= argument defines the portion of the file that the fileReader will read from. This is a byte offset; the beginning of the file is at the offset 0. The default for this argument enables the fileReader to access the entire file.

A fileReader will never read beyond its maximum end position. In addition, reading from a fileReader beyond the end of the underlying file will not extend that file. Reading beyond the end of the file or beyond the end offset of the fileReader will produce the error EEOF (and return false in many cases such as channel.read) to indicate that the end was reached.

Arguments

kind – iokind compile-time argument to determine the corresponding parameter of the fileReader type. Defaults to iokind.dynamic, meaning that the associated iostyle controls the formatting choices.
locking – compile-time argument to determine whether or not the channel should use locking; sets the corresponding parameter of the fileReader type. Defaults to true, but when safe, setting it to false can improve performance.
region – zero-based byte offset indicating where in the file the channel should start and stop reading. Defaults to 0.. - meaning from the start of the file to no end point.
hints – provide hints about the I/O that this channel will perform. See ioHintSet. The default value of ioHintSet.empty will cause the channel to use the hints provided when the file was opened.

Warning

The region argument will ignore any specified stride other than 1.

Throws

SystemError – Thrown if a file reader channel could not be returned.
IllegalArgumentError – Thrown if trying to read explicitly prior to byte 0.

proc file.reader(param kind = iokind.dynamic, param locking = true, region: range(?) = 0.., hints = ioHintSet.empty): fileReader(kind, locking) throws: Warning

Currently the region argument’s high bound specifies the first location in the file that is not included. This behavior is deprecated, please compile your program with -suseNewFileReaderRegionBounds=true to have the region argument specify the entire segment of the file covered, inclusive.

proc file.lines(param locking: bool = true, start: int(64) = 0, end: int(64) = max(int(64)), hints = ioHintSet.empty, in local_style: iostyle) throws¶: Warning

lines with a local_style argument is unstable

config param useNewLinesRegionBounds = false¶: Used to control the behavior of the region argument for file.lines. When set to true, the region argument will fully specify the bounds that this function would cover. When set to false, the region argument will exclude the high bound. Defaults to false, the original behavior.

proc file.lines(param locking: bool = true, region: range(?) = 0.., hints = ioHintSet.empty) throws

Iterate over all of the lines in a file.

Returns: an object which yields strings read from the file
Throws: SystemError – Thrown if an object could not be returned.

proc file.lines(param locking: bool = true, region: range(?) = 0.., hints = ioHintSet.empty) throws: Warning

Currently the region argument’s high bound specifies the first location in the file that is not included. This behavior is deprecated, please compile your program with -suseNewLinesRegionBounds=true to have the region argument specify the entire segment of the file covered, inclusive.

proc file.writer(param kind = iokind.dynamic, param locking = true, start: int(64) = 0, end: int(64) = max(int(64)), hints = ioHintSet.empty, style: iostyle): fileWriter(kind, locking) throws¶: Warning

writer with a style argument is unstable

config param useNewFileWriterRegionBounds = false¶: Used to control the behavior of the region argument for file.writer. When set to true, the region argument will fully specify the bounds of the fileWriter. When set to false, the region argument will exclude the high bound. Defaults to false, the original behavior.

proc file.writer(param kind = iokind.dynamic, param locking = true, region: range(?) = 0.., hints = ioHintSet.empty): fileWriter(kind, locking) throws

Create a fileWriter that supports writing to a file. See I/O Overview.

The region= argument defines the portion of the file that the fileWriter will write to. This is a byte offset; the beginning of the file is at the offset 0. The default for this argument enables the fileWriter to access the entire file.

When a fileWriter writes to a file, it will replace file data that was previously stored at the relevant offset. If the offset is beyond the end of the file, the file will be extended.

A fileWriter will never write beyond its maximum end position. It will extend the file only as necessary to store data written to the fileWriter. In other words, specifying the high bound of the region argument here does not impact the file size directly; it impacts only the section of the file that this fileWriter can write to. After all fileWriters to a file are closed, that file will have a size equal to the last position written to by any fileWriter.

Arguments

kind – iokind compile-time argument to determine the corresponding parameter of the fileWriter type. Defaults to iokind.dynamic, meaning that the associated iostyle controls the formatting choices.
locking – compile-time argument to determine whether or not the channel should use locking; sets the corresponding parameter of the fileWriter type. Defaults to true, but when safe, setting it to false can improve performance.
region – zero-based byte offset indicating where in the file the fileWriter should start and stop writing. Defaults to 0.. - meaning from the start of the file to no specified end point.
hints – provide hints about the I/O that this channel will perform. See ioHintSet. The default value of ioHintSet.empty will cause the fileWriter to use the hints provided when the file was opened.

Warning

The region argument will ignore any specified stride other than 1.

Throws

SystemError – Thrown if a file writer channel could not be returned.
IllegalArgumentError – Thrown if trying to write explicitly prior to byte 0.

proc file.writer(param kind = iokind.dynamic, param locking = true, region: range(?) = 0.., hints = ioHintSet.empty): fileWriter(kind, locking) throws: Warning

Currently the region argument’s high bound specifies the first location in the file that is not included. This behavior is deprecated, please compile your program with -suseNewFileWriterRegionBounds=true to have the region argument specify the entire segment of the file covered, inclusive.

proc channel.readWriteLiteral(lit: string, ignoreWhiteSpace = true) throws¶: Explicit call for reading or writing a literal as an alternative to using IO.ioLiteral.

proc channel.readLiteral(literal: string, ignoreWhitespace = true): void throws¶

Advances the position of a channel by reading the exact text of the given string literal from the channel.

If the string is not matched exactly, then the channel’s position is unchanged. In such cases a OS.BadFormatError will be thrown, unless the end of the channel is encountered in which case an OS.EofError will be thrown. By default this method will ignore leading whitespace when attempting to read a literal.

Arguments

literal – the string to be matched.
ignoreWhitespace – determines whether leading whitespace is ignored.

Throws

BadFormatError – Thrown if literal could not be matched.
EofError – Thrown if end of channel is encountered.

Warning

channel.readLiteral is unstable and subject to change.

proc channel.readLiteral(literal: bytes, ignoreWhitespace = true): void throws

Advances the position of a channel by reading the exact bytes of the given literal from the channel.

If the bytes are not matched exactly, then the channel’s position is unchanged. In such cases a OS.BadFormatError will be thrown, unless the end of the channel is encountered in which case an OS.EofError will be thrown. By default this method will ignore leading whitespace when attempting to read a literal.

Arguments

literal – the bytes to be matched.
ignoreWhitespace – determines whether leading whitespace is ignored.

Throws

BadFormatError – Thrown if literal could not be matched.
EofError – Thrown if end of channel is encountered.

Warning

channel.readLiteral is unstable and subject to change.

proc channel.readNewline(): void throws¶

Advances the position of the channel by reading a newline.

If a newline is not matched exactly, then the channel’s position is unchanged. In such cases a OS.BadFormatError will be thrown, unless the end of the channel is encountered in which case an OS.EofError will be thrown. By default this method will ignore leading whitespace when attempting to read a newline.

Throws

BadFormatError – Thrown if a newline could not be matched.
EofError – Thrown if end of channel is encountered.

Warning

channel.readNewline is unstable and subject to change.

proc channel.matchLiteral(literal: string, ignoreWhitespace = true): bool throws¶

Advances the position of a channel by reading the exact text of the given string literal from the channel.

If the string is not matched exactly, then the channel’s position is unchanged and this method will return false. In other words, this channel will return false in the cases where channel.readLiteral would throw a OS.BadFormatError or an OS.EofError.

By default this method will ignore leading whitespace when attempting to read a literal.

Arguments

literal – the string to be matched.
ignoreWhitespace – determines whether leading whitespace is ignored.

Returns

true if the read succeeded, and false on end of file or if the literal could not be matched.

Warning

channel.matchLiteral is unstable and subject to change.

proc channel.matchLiteral(literal: bytes, ignoreWhitespace = true): bool throws

Advances the position of a channel by reading the exact bytes of the given literal from the channel.

If the bytes are not matched exactly, then the channel’s position is unchanged and this method will return false. In other words, this channel will return false in the cases where channel.readLiteral would throw a OS.BadFormatError or an OS.EofError.

By default this method will ignore leading whitespace when attempting to read a literal.

Arguments

literal – the bytes to be matched.
ignoreWhitespace – determines whether leading whitespace is ignored.

Returns

true if the read succeeded, and false on end of file or if the literal could not be matched.

Warning

channel.matchLiteral is unstable and subject to change.

proc channel.matchNewline(): bool throws¶

Advances the position of the channel by reading a newline.

If a newline is not matched exactly, then the channel’s position is unchanged and this method will return false. In other words, this channel will return false in the cases where channel.readNewline would throw a OS.BadFormatError or an OS.EofError.

By default this method will ignore leading whitespace when attempting to read a newline.

Returns: true if the read succeeded, and false on end of file or if the newline could not be matched.

Warning

channel.matchNewline is unstable and subject to change.

proc channel.writeLiteral(literal: string): void throws¶: Writes a string to the channel, ignoring any formatting configured for this channel.

Warning

channel.writeLiteral is unstable and subject to change.

proc channel.writeLiteral(literal: bytes): void throws: Writes bytes to the channel, ignoring any formatting configured for this channel.

Warning

channel.writeLiteral is unstable and subject to change.

proc channel.writeNewline(): void throws¶: Writes a newline to the channel, ignoring any formatting configured for this channel.

Warning

channel.writeNewline is unstable and subject to change.

proc channel.readWriteNewline() throws¶: Explicit call for reading or writing a newline as an alternative to using IO.ioNewline.

proc channel.binary(): bool¶: Returns true if this channel is configured for binary I/O.

proc channel.writeBytes(x, len: c_ssize_t) throws¶

Write a sequence of bytes.

Throws: SystemError – Thrown if the byte sequence could not be written.

iter channel.lines()¶

Iterate over all of the lines ending in \n in a channel - the channel lock will be held while iterating over the lines.

Only serial iteration is supported.

Warning

This iterator executes on the current locale. This may impact multilocale performance if the current locale is not the same locale on which the channel was created.

Yields: lines ending in \n in channel

proc stringify(const args ...?k): string¶

Creates a string representing the result of writing the arguments.

Writes each argument, possibly using a writeThis method, to a string and returns the result.

proc channel.read(ref args ...?k): bool throws¶

Read values from a channel. The input will be consumed atomically - the channel lock will be held while reading all of the passed values.

Arguments: args – a list of arguments to read. Basic types are handled internally, but for other types this function will call value.readThis() with a Reader argument as described in The readThis() and writeThis() Methods.
Returns: true if the read succeeded, and false on end of file.
Throws: SystemError – Thrown if the channel could not be read.

proc channel.read(ref args ...?k, style: iostyle): bool throws: Warning

read with a style argument is unstable

proc channel.readline(arg: [] uint(8), out numRead: int, start = arg.domain.lowBound, amount = arg.domain.highBound - start + 1): bool throws¶

Read a line into a Chapel array of bytes. Reads until a \n is reached. The \n is returned in the array.

Note that this routine currently requires a 1D rectangular non-strided array.

Throws a SystemError if a line could not be read from the channel.

Arguments

arg – A 1D DefaultRectangular array which must have at least 1 element.
numRead – The number of bytes read.
start – Index to begin reading into.
amount – The maximum amount of bytes to read.

Returns

true if the bytes were read without error.

Warning

channel.readline is deprecated. Use channel.readLine instead

proc channel.readLine(ref a: [] ?t, maxSize = a.size, stripNewline = false): int throws¶

Read a line into a Chapel array of bytes. Reads until a \n is reached. This function always does a binary read (i.e. it is not aware of UTF-8 etc) and is similar in some ways to readLine(bytes) but works with an array directly. However, it does not resize the array but rather stores up to first ‘size’ bytes in to it. The exact number of bytes in the array set will depend on the line length (and on stripNewline since the newline will be counted if it is stored in the array).

Arguments

a – A 1D DefaultRectangular non-strided array storing int(8) or uint(8) which must have at least 1 element.
maxSize – The maximum number of bytes to store into the a array. Defaults to the size of the array.
stripNewline – Whether to strip the trailing \n from the line.

Returns

Returns 0 if EOF is reached and no data is read. Otherwise, returns the number of array elements that were set by this call.

Throws

SystemError – Thrown if data could not be read from the channel.
IoError – Thrown if the line is longer than maxSize. It leaves the input marker at the beginning of the offending line.

proc channel.readline(ref arg: ?t): bool throws

Read a line into a Chapel string or bytes. Reads until a \n is reached. The \n is included in the resulting value.

Arguments: arg – a string or bytes to receive the line
Returns: true if a line was read without error, false upon EOF
Throws: SystemError – Thrown if data could not be read from the channel.

Warning

channel.readline is deprecated. Use channel.readLine instead

proc channel.readLine(ref s: string, maxSize = -1, stripNewline = false): bool throws

Read a line into a Chapel string. Reads until a \n is reached.

Arguments

s – a string to receive the line
maxSize – The maximum number of codepoints to store into s. The default of -1 means to read an unlimited number of codepoints.
stripNewline – Whether to strip the trailing \n from the line.

Returns

true if a line was read without error, false upon EOF

Throws

SystemError – Thrown if data could not be read from the channel.
IoError – Thrown if the line is longer than maxSize. It leaves the input marker at the beginning of the offending line.

proc channel.readLine(ref b: bytes, maxSize = -1, stripNewline = false): bool throws

Read a line into Chapel bytes. Reads until a \n is reached.

Arguments

b – bytes to receive the line
maxSize – The maximum number of bytes to store into b. The default of -1 means to read an unlimited number of bytes.
stripNewline – Whether to strip the trailing \n from the line.

Returns

true if a line was read without error, false upon EOF

Throws

SystemError – Thrown if data could not be read from the channel.
IoError – Thrown if the line is longer than maxSize. It leaves the input marker at the beginning of the offending line.

proc channel.readLine(type t = string, maxSize = -1, stripNewline = false): t throws

Read a line. Reads until a \n is reached.

Arguments

t – the type of data to read, which must be string or bytes. Defaults to string if not specified.
maxSize – The maximum number of codepoints to read. The default of -1 means to read an unlimited number of codepoints.
stripNewline – Whether to strip the trailing \n from the line.

Returns

The data that was read.

Throws

SystemError – Thrown if data could not be read from the channel.
IoError – Thrown if the line is longer than maxSize. It leaves the input marker at the beginning of the offending line.

proc channel.readAll(type t = bytes): t throws¶

Read the remaining contents of the channel into an instance of the specified type

Arguments: t – the type to read into; must be string or bytes. Defaults to bytes if not specified.
Returns: the contents of the channel as a t
Throws: SystemError – Thrown if data could not be read from the channel

proc channel.readAll(ref s: string): int throws

Read the remaining contents of the channel into a string.

Note that any existing contents of the string are overwritten.

Arguments: s – the string to read into
Returns: the number of codepoints that were stored in s
Return type: int
Throws: SystemError – Thrown if data could not be read from the channel

proc channel.readAll(ref b: bytes): int throws

Read the remaining contents of the channel into a bytes.

Note that any existing contents of the bytes are overwritten.

Arguments: b – the bytes to read into
Returns: the number of bytes that were stored in b
Return type: int
Throws: SystemError – Thrown if data could not be read from the channel

proc channel.readAll(ref a: [?d] ?t): int throws

Read the remaining contents of the channel into a an array of bytes.

Note that this routine currently requires a 1D rectangular non-strided array. Additionally, If the remaining contents of the channel exceed the size of a, the first a.size bytes will be read into a, and then an InsufficientCapacityError will be thrown.

Arguments

a – the array of bytes to read into

Returns

the number of bytes that were stored in a

Return type

int

Throws

InsufficientCapacityError – Thrown if the channel’s contents do not fit into a
SystemError – Thrown if data could not be read from the channel

proc channel.readstring(ref str_out: string, len: int(64) = -1): bool throws¶

read a given number of bytes from a channel

Arguments

str_out – The string to be read into
len – Read up to len bytes from the channel, up until EOF (or some kind of I/O error). If the default value of -1 is provided, read until EOF starting from the channel’s current offset.

Returns

true if we read something, false upon EOF

Throws

SystemError – Thrown if the bytes could not be read from the channel.

proc channel.readbytes(ref bytes_out: bytes, len: int(64) = -1): bool throws¶

read a given number of bytes from a channel

Arguments

bytes_out – The bytes to be read into
len – Read up to len bytes from the channel, up until EOF (or some kind of I/O error). If the default value of -1 is provided, read until EOF starting from the channel’s current offset.

Returns

true if we read something, false upon EOF

Throws

SystemError – Thrown if the bytes could not be read from the channel.

proc channel.readbits(ref v: integral, nbits: integral): bool throws¶

Read bits with binary I/O

Arguments

v – where to store the read bits. This value will have its nbits least-significant bits set.
nbits – how many bits to read

Returns

true if the bits were read without error, false upon EOF

Throws

SystemError – Thrown if the bits could not be read from the channel.

proc channel.writebits(v: integral, nbits: integral) throws¶

Write bits with binary I/O

Arguments

v – a value containing nbits bits to write the least-significant bits
nbits – how many bits to write

Throws

IllegalArgumentError – Thrown if writing more bits than fit into v.
SystemError – Thrown if the bits could not be written to the channel.

proc fileWriter.writeBinary(ptr: c_ptr(?t), numBytes: int) throws¶

Write numBytes of data from a c_ptr to a fileWriter

Note that native endianness is always used.

If numBytes is not evenly divisible by the size of t, the remaining bytes will be ignored. For example, if the c_ptr’s internal type is 4 bytes in length, and numBytes=17, only 16 bytes will be written.

Warning

This method provides no protection against attempting to access invalid memory

Arguments

ptr – a c_ptr to some valid memory
numBytes – the number of bytes to write

Throws

SystemError – Thrown if an error occured while writing to the fileWriter

proc fileWriter.writeBinary(ptr: c_void_ptr, numBytes: int) throws

Write numBytes of data from a c_void_ptr to a fileWriter

The data are written to the file one byte at a time.

Warning

This method provides no protection against attempting to access invalid memory

Arguments

ptr – a typeless c_void_ptr to some valid memory
numBytes – the number of bytes to write

Throws

SystemError – Thrown if an error occured while writing to the fileWriter

proc channel.writeBinary(arg: numeric, param endian: ioendian = ioendian.native) throws¶

Write a binary number to the channel

Arguments

arg – number to be written
endian – ioendian compile-time argument that specifies the byte order in which to write the number. Defaults to ioendian.native.

Throws

SystemError – Thrown if the number could not be written to the channel.

proc channel.writeBinary(arg: numeric, endian: ioendian) throws

Write a binary number to the channel

Arguments

arg – number to be written
endian – ioendian specifies the byte order in which to write the number.

Throws

SystemError – Thrown if the number could not be written to the channel.

proc fileWriter.writeBinary(s: string, size: int = s.size) throws

Write a string to a fileWriter in binary format

Arguments

s – the string to write
size – the number of codepoints to write from the string

Throws

SystemError – Thrown if the string could not be written to the fileWriter.
IllegalArgumentError – Thrown if size is larger than s.size

proc fileWriter.writeBinary(b: bytes, size: int = b.size) throws

Write a bytes to a fileWriter in binary format

Arguments

b – the bytes to write
size – the number of bytes to write from the bytes

Throws

SystemError – Thrown if the bytes could not be written to the fileWriter.
IllegalArgumentError – Thrown if size is larger than b.size

proc fileWriter.writeBinary(const ref data: [?d] ?t, param endian: ioendian = ioendian.native) throws

Write an array of binary numbers to a fileWriter

Note that this routine currently requires a 1D rectangular non-strided array.

Arguments

data – an array of numbers to write to the fileWriter
endian – ioendian compile-time argument that specifies the byte order in which to read the numbers. Defaults to ioendian.native.

Throws

SystemError – Thrown if the values could not be written to the fileWriter.
UnexpectedEofError – Thrown if EOF is reached before all the values could be written.

proc fileWriter.writeBinary(const ref data: [?d] ?t, endian: ioendian) throws

Write an array of binary numbers to a fileWriter

Note that this routine currently requires a 1D rectangular non-strided array.

Arguments

data – an array of numbers to write to the fileWriter
endian – ioendian specifies the byte order in which to write the number.

Throws

SystemError – Thrown if the values could not be written to the fileWriter.
UnexpectedEofError – Thrown if EOF is reached before all the values could be written.

proc channel.readBinary(ref arg: numeric, param endian: ioendian = ioendian.native): bool throws¶

Read a binary number from the channel

Arguments

arg – number to be read
endian – ioendian compile-time argument that specifies the byte order in which to read the number. Defaults to ioendian.native.

Returns

true if the number was read, false otherwise

Throws

SystemError – Thrown if an error occurred reading the number.

proc channel.readBinary(ref arg: numeric, endian: ioendian): bool throws

Read a binary number from the channel

Arguments

arg – number to be read
endian – ioendian specifies the byte order in which to read the number.

Returns

true if the number was read, false otherwise

Throws

SystemError – Thrown if an error occurred reading the number.

proc fileReader.readBinary(ref s: string, maxSize: int): bool throws¶

Read a specified number of codepoints into a string

The string s may be smaller than maxSize if EOF is reached before reading the specified number of codepoints. Additionally, if nothing is read from the fileReader, s will be set to "" (the empty string) and the method will return false.

Note

This method always uses UTF-8 encoding regardless of the fileReader’s configuration

Arguments

s – the string to read into — this value is overwritten
maxSize – the number of codepoints to read from the fileReader

Returns

false if EOF is reached before reading anything, true otherwise

Throws

SystemError – Thrown if an error occurred while reading from the fileReader.

proc fileReader.readBinary(ref b: bytes, maxSize: int): bool throws

Read a specified number of bytes into a bytes

The bytes b may be smaller than maxSize if EOF is reached before reading the specified number of bytes. Additionally, if nothing is read from the fileReader, b will be set to b"" (the empty bytes) and the method will return false.

Arguments

b – the bytes to read into — this value is overwritten
maxSize – the number of bytes to read from the fileReader

Returns

false if EOF is reached before reading anything, true otherwise

Throws

SystemError – Thrown if an error occurred while reading from the fileReader.

proc fileReader.readBinary(ref data: [?d] ?t, param endian = ioendian.native): bool throws

Read an array of binary numbers from a fileReader

Binary values of the type data.eltType are consumed from the fileReader until data is full or EOF is reached. An UnexpectedEofError is thrown if EOF is reached before the array is filled.

Note that this routine currently requires a 1D rectangular non-strided array.

Arguments

data – an array to read into – existing values are overwritten.
endian – ioendian compile-time argument that specifies the byte order in which to read the numbers. Defaults to ioendian.native.

Returns

false if EOF is encountered before reading anything, true otherwise

Throws

SystemError – Thrown if an error occurred while reading from the fileReader
UnexpectedEofError – Thrown if EOF is encountered before data.size values are read

proc fileReader.readBinary(ref data: [?d] ?t, endian: ioendian): bool throws

Read an array of binary numbers from a fileReader

Binary values of the type data.eltType are consumed from the fileReader until data is full or EOF is reached. An UnexpectedEofError is thrown if EOF is reached before the array is filled.

Note that this routine currently requires a 1D rectangular non-strided array.

Arguments

data – an array to read into – existing values are overwritten.
endian – ioendian specifies the byte order in which to read the number.

Returns

false if EOF is encountered before reading anything, true otherwise

Throws

SystemError – Thrown if an error occurred while reading the from fileReader
UnexpectedEofError – Thrown if EOF is encountered before data.size values are read

proc fileReader.readBinary(ptr: c_ptr(?t), maxBytes: int): int throws

Read up to maxBytes bytes from a fileReader into a c_ptr

Note that native endianness is always used.

If maxBytes is not evenly divisible by the size of t, then the remaining bytes are ignored.

Arguments

ptr – a c_ptr to some memory — existing values will be overwritten
maxBytes – the maximum number of bytes to read from the fileReader

Returns

the number of bytes that were read. this can be less than maxBytes if EOF was reached before reading the specified number of bytes, or if maxBytes is not evenly divisible by the size of t

Throws

SystemError – Thrown if an error occurred while reading from the fileReader

proc fileReader.readBinary(ptr: c_void_ptr, maxBytes: int): int throws

Read up to maxBytes bytes from a fileReader into a c_void_ptr

Note that data are read from the file one byte at a time.

Arguments

ptr – a typeless c_void_ptr to some memory — existing values will be overwritten
maxBytes – the maximum number of bytes to read from the fileReader

Returns

the number of bytes that were read. this can be less than maxBytes if EOF was reached before reading the specified number of bytes

Throws

SystemError – Thrown if an error occurred while reading from the fileReader

proc channel.readln(ref args ...?k): bool throws¶

Read values from a channel and then consume any bytes until newline is reached. The input will be consumed atomically - the channel lock will be held while reading all of the passed values.

Arguments: args – a list of arguments to read. This routine can be called with zero or more such arguments. Basic types are handled internally, but for other types this function will call value.readThis() with a Reader argument as described in The readThis() and writeThis() Methods.
Returns: true if the read succeeded, and false upon end of file.
Throws: SystemError – Thrown if a line could not be read from the channel.

proc channel.readln(ref args ...?k, style: iostyle): bool throws: Warning

readln with a style argument is unstable

proc channel.read(type t) throws

Read a value of passed type.

For example, the following line of code reads a value of type int from stdin and uses it to initialize a variable x:

var x = stdin.read(int)

Arguments: t – the type to read
Returns: the value read
Throws: SystemError – Thrown if the type could not be read from the channel.

proc channel.readln(type t) throws

Read a value of passed type followed by a newline.

Arguments: t – the type to read
Returns: the value read
Throws: SystemError – Thrown if the type could not be read from the channel.

proc channel.readln(type t ...?numTypes) throws

Read values of passed types followed by a newline and return a tuple containing the read values.

Arguments: t – more than one type to read
Returns: a tuple of the read values
Throws: SystemError – Thrown if the types could not be read from the channel.

proc channel.read(type t ...?numTypes) throws

Read values of passed types and return a tuple containing the read values.

Arguments: t – more than one type to read
Returns: a tuple of the read values
Throws: SystemError – Thrown if the types could not be read from the channel.

proc channel.write(const args ...?k) throws¶

Write values to a channel. The output will be produced atomically - the channel lock will be held while writing all of the passed values.

Arguments

args – a list of arguments to write. Basic types are handled internally, but for other types this function will call value.writeThis() with the channel as an argument.

Throws

SystemError – Thrown if the values could not be written to the channel.
EofError – Thrown if EOF is reached before all the arguments could be written.

proc channel.write(const args ...?k, style: iostyle) throws: Warning

write with a style argument is unstable

proc channel.writeln(const args ...?k) throws¶

Write values to a channel followed by a newline. The output will be produced atomically - the channel lock will be held while writing all of the passed values.

Arguments

args – a variable number of arguments to write. This method can be called with zero or more arguments. Basic types are handled internally, but for other types this function will call value.writeThis() with the channel as an argument.

Throws

SystemError – Thrown if the values could not be written to the channel.
EofError – Thrown if EOF is reached before all the arguments could be written.

proc channel.writeln(const args ...?k, style: iostyle) throws: Warning

writeln with a style argument is unstable

proc channel.flush() throws¶

Makes all writes to the channel, if any, available to concurrent viewers of its associated file, such as other channels or other applications accessing this file concurrently. Unlike file.fsync, this does not commit the written data to the file’s device.

Throws: SystemError – Thrown if the flush fails.

proc channel.assertEOF(errStr: string = "- Not at EOF")¶: Assert that a channel has reached end-of-file and that there was no error doing the read.

proc channel.close() throws¶

Close a channel. Implicitly performs the channel.flush operation (see Synchronization of Channel Data and Avoiding Data Races).

Throws: SystemError – Thrown if the channel is not successfully closed.

proc channel.isClosed(): bool¶: Return true if a channel is currently closed.

proc channel.isclosed(): bool¶: Warning

channel.isclosed is deprecated. Please use channel.isClosed instead

const stdin: fileReader(iokind.dynamic, true)¶: standard input, otherwise known as file descriptor 0

const stdout: fileWriter(iokind.dynamic, true)¶: standard output, otherwise known as file descriptor 1

const stderr: fileWriter(iokind.dynamic, true)¶: standard error, otherwise known as file descriptor 2

proc read(ref args ...?n): bool throws¶: Equivalent to stdin.read. See channel.read

proc read(type t ...?numTypes) throws: Equivalent to stdin.read. See channel.read for types

proc readLine(ref a: [] ?t, maxSize = a.size, stripNewline = false): int throws¶: Equivalent to stdin.readLine. See channel.readLine

proc readline(arg: [] uint(8), out numRead: int, start = arg.domain.lowBound, amount = arg.domain.highBound - start + 1): bool throws¶: Equivalent to stdin.readline. See channel.readline

Warning

readline is deprecated. Use readLine instead

proc readline(ref arg: ?t): bool throws: Equivalent to stdin.readline. See channel.readline

Warning

readline is deprecated. Use readLine instead

proc readLine(ref s: string, maxSize = -1, stripNewline = false): bool throws: Equivalent to stdin.readLine. See channel.readLine

proc readLine(ref b: bytes, maxSize = -1, stripNewline = false): bool throws: Equivalent to stdin.readLine. See channel.readLine

proc readLine(type t = string, maxSize = -1, stripNewline = false): t throws: Equivalent to stdin.readLine. See channel.readLine

proc readln(ref args ...?n): bool throws¶: Equivalent to stdin.readln. See channel.readln

proc readln(type t ...?numTypes) throws: Equivalent to stdin.readln. See channel.readln for types

proc unicodeSupported(): bool¶

Returns: true if this version of the Chapel runtime supports UTF-8 output.

Warning

unicodeSupported is deprecated due to always returning true

proc file.localesForRegion(start: int(64), end: int(64))¶

Returns the ‘best’ locale to run something working with the region of the file in start..end-1.

This must return the same result when called from different locales. Returns a domain of locales that are “best” for the given region. If no locales are “best” we return a domain containing all locales.

Arguments

start – the file offset (starting from 0) where the region begins
end – the file offset just after the region

Returns

a set of locales that are best for working with this region

Return type

domain(locale)

Warning

file.localesForRegion is deprecated

IO¶

I/O Overview¶

Design Rationale¶

I/O Styles¶

Files¶

Functions for Channel Creation¶

Synchronization of Channel Data and Avoiding Data Races¶

Performing I/O with Channels¶

Functions for Closing Channels¶

The stdin, stdout, and stderr Channels¶

Error Handling¶

Ensuring Successful I/O¶

Correspondence with C I/O¶

IO Functions and Types¶

The `stdin`, `stdout`, and `stderr` Channels¶