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

Solution

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