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c c99 inline-functions linker

How to declare an inline function in C99 multi-file project?

I want to define an inline function in a project, compiled with c99. How can I do it?
When I declare the function in a header file and give the detail in a .c file, the definition isn’t recognized by other files. When I put the explicit function in a header file, I have a problem because all .o files who use it have a copy of the definition, so the linker gives me a “multiple definition” error.

What I am trying to do is something like:

header.h
inline void func()
{
do things...
}
lib1.c
#include "header.h"
...
lib2.c
#include "header.h"

with a utility which uses both lib1.o and lib2.o

Unfortunately not all compilers are completely complying to C99 in that point even if they claim that they’d be.

An conforming way to do this is

// header file. an inline definition alone is
// not supposed to generate an external symbol
inline void toto(void) {
// do something
}
// in one .c file, force the creation of an
// external symbol
extern inline void toto(void);

Newer versions of gcc, e.g, will work fine with that.

You may get away with it for other compilers (pretenders) by defining something like

#ifdef PRETENDER
# define inlDec static
# define inlIns static
#else
# define inlDec
# define inlIns extern
#endif
// header file. an inline declaration alone is
// not supposed to generate an external symbol
inlDec inline void toto(void) {
// do something
}
// in one .c file, force the creation of an
// external symbol
inlIns inline void toto(void);

Edit:

compilers with C99 support (usually option -std=c99) that I know of

  • gcc (versions >= 4.3 IIRC) implements
    the correct inline model
  • pcc is also correct
  • ggc < 4.3 needs a special option to
    implement the correct model,
    otherwise they use their own model
    that results in multiple defined
    symbols if you are not careful
  • icc just emits symbols in every unit
    if you don’t take special care. But
    these symbols are “weak” symbols, so
    they don’t generate a conflict. They
    just blow up your code.
  • opencc, AFAIR, follows the old gcc specific model
  • clang doesn’t emit symbols for inline functions at all, unless you have an extern declaration and you use the function pointer in one compilation unit.
  • tcc just ignores the inline keyword