ChapelIO¶
Note
All Chapel programs automatically use
this module by default.
An explicit use
statement is not necessary.
Basic types and utilities in support of I/O operation.
Most of Chapel’s I/O support is within the IO
module. This section
describes automatically included basic types and routines that support the
IO
module.
Writing¶
The writeln
function allows for a simple implementation
of a Hello World program:
writeln("Hello, World!");
// outputs
// Hello, World!
The readThis() and writeThis() Methods¶
A Chapel program can implement readThis
and writeThis
methods on a
custom data type to define how that type is read from a fileReader or written to
a fileWriter. readThis
accepts a fileReader as its only argument and the
file must be readable. writeThis
accepts a fileWriter as its only argument
and the file must be writable. If neither of these methods is defined, a default
version of readThis
and writeThis
will be generated by the compiler.
Note that arguments to readThis
and writeThis
may be locked; as a
result, calling methods on the fileReader or fileWriter in parallel from within
a readThis
or writeThis
may cause undefined behavior. Additionally,
performing I/O on a global fileReader or fileWriter that is the same as the one
readThis
or writeThis
is operating on can result in a deadlock. In
particular, these methods should not refer to stdin
,
stdout
, or stderr
explicitly or implicitly (such as by
calling the global writeln
function). Instead, these methods should
only perform I/O on the fileReader or fileWriter passed as an argument.
Note that the types IO.ioLiteral
and IO.ioNewline
may be useful
when implementing readThis
and writeThis
methods. IO.ioLiteral
represents some string that must be read or written as-is (e.g. ","
when
working with a tuple), and IO.ioNewline
will emit a newline when
writing but skip to and consume a newline when reading. Note that these types
are not included by default.
This example defines a writeThis method - so that there will be a function resolution error if the record NoRead is read.
record NoRead {
var x: int;
var y: int;
proc writeThis(f) throws {
f.write("hello");
}
// Note that no readThis function will be generated.
}
var nr = new NoRead();
write(nr);
// prints out
// hello
// Note that read(nr) will generate a compiler error.
Default writeThis and readThis Methods¶
Default writeThis
methods are created for all types for which a
user-defined writeThis
method is not provided. They have the following
semantics:
for a class: outputs the values within the fields of the class prefixed by the name of the field and the character
=
. Each field is separated by a comma. The output is delimited by{
and}
.for a record: outputs the values within the fields of the class prefixed by the name of the field and the character
=
. Each field is separated by a comma. The output is delimited by(
and)
.
Default readThis
methods are created for all types for which a user-defined
readThis
method is not provided. The default readThis
methods are
defined to read in the output of the default writeThis
method.
Additionally, the Chapel implementation includes writeThis
methods for
built-in types as follows:
for an array: outputs the elements of the array in row-major order where rows are separated by line-feeds and blank lines are used to separate other dimensions.
for a domain: outputs the dimensions of the domain enclosed by
{
and}
.for a range: output the lower bound of the range, output
..
, then output the upper bound of the range. If the stride of the range is not1
, output the wordby
and then the stride of the range. If the range has special alignment, output the wordalign
and then the alignment.for tuples, outputs the components of the tuple in order delimited by
(
and)
, and separated by commas.
These types also include readThis
methods to read the corresponding format.
Note that when reading an array, the domain of the array must be set up
appropriately before the elements can be read.
Note
Note that it is not currently possible to read and write circular data structures with these mechanisms.
- proc write(const args ...?n)¶
Equivalent to
try! stdout.write
. SeeIO.fileWriter.write
- proc writeln(const args ...?n)¶
Equivalent to
try! stdout.writeln
. SeeIO.fileWriter.writeln
- proc writef(fmt: ?t, const args ...?k)¶
Equivalent to
try! stdout.writef
. SeeFormattedIO.fileWriter.writef
.