D binding for C

While D cannot directly compile C source code, it can easily interface to C code, be linked with C object files, and call C functions in DLLs. The interface to C code is normally found in C .h files. So, the trick to connecting with C code is in converting C .h files to D modules. This turns out to be difficult to do mechanically since inevitably some human judgement must be applied. This is a guide to doing such conversions.

Preprocessor

.h files can sometimes be a bewildering morass of layers of macros, #include files, #ifdef's, etc. D doesn't include a text preprocessor like the C preprocessor, so the first step is to remove the need for it by taking the preprocessed output. For DMC (the Digital Mars C/C++ compiler), the command:

dmc -c program.h -e -l

will create a file program.lst which is the source file after all text preprocessing.

Remove all the #if, #ifdef, #include, etc. statements.

Linkage

Generally, surround the entire module with:

extern (C)
{
     /* ...file contents... */
}

to give it C linkage.

Types

A little global search and replace will take care of renaming the C types to D types. The following table shows a typical mapping for 32 bit C code:

Mapping C type to D type

C type	D type
long double	real
unsigned long long	ulong
long long	long
unsigned long	uint
long	int
unsigned	uint
unsigned short	ushort
signed char	byte
unsigned char	ubyte
wchar_t	wchar or dchar
bool	bool, byte, int
size_t	size_t
ptrdiff_t	ptrdiff_t