c++ - Is extern "C" only required on the function declaration?

Question

I wrote a C++ function that I need to call from a C program. To make it callable from C, I specified extern "C" on the function declaration. I then compiled the C++ code, but the compiler (Dignus Systems/C++) generated a mangled name for the function. So, it apparently did not honor the extern "C".

To resolve this, I added extern "C" to the function definition. After this, the compiler generated a function name that is callable from C.

Technically, the extern "C" only needs to be specified on the function declaration. Is this right? (The C++ FAQ has a good example of this.) Should you also specify it on the function definition?

Here's an example to demonstrate this:

/* ---------- */
/* "foo.h"    */
/* ---------- */

#ifdef __cplusplus
extern "C" {
#endif

/* Function declaration */
void foo(int);

#ifdef __cplusplus
}
#endif

/* ---------- */
/* "foo.cpp"  */
/* ---------- */

#include "foo.h"

/* Function definition */
extern "C"               // <---- Is this needed?
void foo(int i) {
  // do something...
}

My issue may be the result of incorrectly coding something, or I may have found a compiler bug. In any case, I wanted to consult stackoverflow to make sure I know which is technically the "right" way.

question from:https://stackoverflow.com/questions/1380829/is-extern-c-only-required-on-the-function-declaration