# c2chapel¶

## A tool to generate C bindings for Chapel¶

c2chapel is a tool to help the Chapel programmer generate extern types, records, and procedures when given a C99 file. For example, given the following function declaration in a header file:

void foo(char* str, int n);


c2chapel will generate Chapel code similar to:

extern proc foo(str: c_string, n : c_int) : void;


## Prerequisites¶

This tool has the following prerequisites:

• A Unix-like environment (something with commands like cd, mkdir, rm, etc.)
• A GNU-compatible version of 'make'
• A C preprocessor
• Python 2.7 or Python 3.5

Other versions of Python may work, but only 2.7 and 3.5 have been tested as of version 0.1.0.

## Building¶

c2chapel is built on top of pycparser. Building c2chapel will install pycparser into a local virtualenv, leaving the user's python environment untouched. A symbolic link will be created in the appropriate directory under $CHPL_HOME/bin. To build, run make c2chapel from $CHPL_HOME.

If virtualenv is not installed, this build process will attempt to use a local virtualenv installation generated by other Chapel make targets if one is available. For example, make test-venv from $CHPL_HOME will create a local virtualenv installation that can be used by the c2chapel build process. Once installed, c2chapel should be visible in your $PATH provided you have sourced a script like $CHPL_HOME/util/setchplenv.bash (also used to make the chpl compiler available to your path). To test the c2chapel installation, you can run make check from tools/c2chapel/. To remove c2chapel and files generated during the build process, execute one of the following commands from tools/c2chapel/: make clean make cleanall make clobber  A make clobber from $CHPL_HOME will also remove c2chapel.

## Usage¶

c2chapel requires the name of a C99-compliant file, and emits the generated Chapel code to stdout. For example, once installed you can run the following command from within tools/c2chapel/:

c2chapel test/fnints.h


The resulting output should be identical to tools/c2chapel/test/fnints.chpl. Run c2chapel with the --help flag to show more options:

usage: c2chapel [-h] [--no-typedefs] [--debug] [--no-fake-headers]
file [cppFlags [cppFlags ...]]

Generate C bindings for Chapel

positional arguments:
file               C99 file for which to generate bindings
cppFlags           flags forwarded to the C preprocessor (invoked with cc
-E)

optional arguments:
-h, --help         show this help message and exit
--no-typedefs      do not generate extern types for C typedefs
--debug            enable debugging output
-V, --version      show program's version number and exit


c2chapel by default uses the fake standard headers included with pycparser. These are headers used to work around compiler-specific macros or attributes often found in C standard headers. Without these fake headers, pycparser will probably not be able to parse the given C99 file. Usage of these fake headers can be disabled with the --no-fake-headers flag. You can extend the fake headers by modifying tools/c2chapel/utils/custom.h.

## Future Work¶

c2chapel does not currently handle the entirety of C99, so some human intervention may be required (e.g. commenting out unhandled portions of the file). There are also some limitations based on Chapel's extern capability. See https://chapel-lang.org/bugs.html for instructions on reporting bugs.

Known issues:

• fake standard headers are incomplete
• choice between ref/c_ptr for formals is not intuitive or easily controlled

## Contributors¶

Ben Harshbarger [Cray Inc.]