How can I create a C++ function f(int,char,float) that is callable by my C code?, C++ FAQ

C++ FAQ / Section 32 / FAQ 32.6

Section 32:

32.1	What do I need to know when mixing C and C++ code?
32.2	How can I include a standard C header file in my C++ code?
32.3	How can I include a non-system C header file in my C++ code?
32.4	How can I modify my own C header files so it's easier to `#include` them in C++ code?
32.5	How can I call a non-system C function `f(int,char,float)` from my C++ code?
32.6	How can I create a C++ function `f(int,char,float)` that is callable by my C code?
32.7	Why is the linker giving errors for C/C++ functions being called from C++/C functions?
32.8	How can I pass an object of a C++ `class` to/from a C function?
32.9	Can my C function directly access data in an object of a C++ `class`?
32.10	Why do I feel like I'm "further from the machine" in C++ as opposed to C?

[32.6] How can I create a C++ function f(int,char,float) that is callable by my C code?

The C++ compiler must know that f(int,char,float) is to be called by a C compiler using the extern "C" construct:

// This is C++ code

// Declare f(int,char,float) using extern "C":
extern "C" void f(int i, char c, float x);

...

// Define f(int,char,float) in some C++ module:
void f(int i, char c, float x)
{
  ...
}

The extern "C" line tells the compiler that the external information sent to the linker should use C calling conventions and name mangling (e.g., preceded by a single underscore). Since name overloading isn't supported by C, you can't make several overloaded functions simultaneously callable by a C program.