While D has binary compatibility with C it is not source compatible.
There are two parts to interfacing with C: name mangling and calling convention.
This is achieved with the use of the extern(C) linkage attribute.
For variables only the name needs to match, but classic C style global variables
should also have __gshared storage class to indicate that they are not thread local.
Globals defined with __thread do not require __gshared.
For functions both the name and the calling convention need to match. In most cases
extern(C) does both, except for (D) static nested functions and static (struct/class)
member functions which only affect the calling convention. This is so they can e.g. be templated.
__cdecl is the calling convention for windows and is covered with extern(Windows).
extern(System) is extern(Windows) on Windows and extern(C) on other systems.
extern(System) should be used for the C idiom
#ifdef (WINDOWS)
#define FOO_API __cdecl
#else
#define FOO_API
#endif
int FOO_API foo(int);in D becomes:
extern(System) int foo(int);There are a number of tools to Automate the translation of C headers to D