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:
| 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 |
NULL
NULL and ((void*)0) should be replaced with null. Numeric Literals Any ‘L’ or ‘l’ numeric literal suffixes should be removed, as a C long is (usually) the same size as a D int. Similarly, ‘LL’ suffixes should be replaced with a single ‘L’. Any ‘u’ suffix will work the same in D.
String Literals
In most cases, any ‘L’ prefix to a string can just be dropped, as D will implicitly convert strings to wide characters if necessary. However, one can also replace:
L"string"
with:
"string"w // for 16 bit wide characters
"string"d // for 32 bit wide characters
