CODEWITHSUNDEEP
c++cexternlinkage
CodeKingPlusPlus
CodeKingPlusPlus

Reputation: 16081

C and C++ linkage with extern "C"

I have a C++ function defined in a .h file as follows and implemented in a .cpp file:

extern "C" void func(bool first, float min, float* state[6], float* err[6][6])
{
    //uses vectors and classes and other C++ constructs
}

How can I call func in a C file? How do I set up my file architecture / makefile to compile this?

Thanks!

Upvotes: 5

Views: 13235

Answers (4)

Josh Petitt
Josh Petitt

Reputation: 9589

call it in C using

func(/* put arguments here */);

By saying extern "C" you are asking the compiler not to mangle your names. Otherwise, C++ compiler would tend to mangle them (i.e. add additional symbols to make them unique) before the linker.

You'll also want to make sure you have setup to use C calling convention.

Upvotes: 3

bames53
bames53

Reputation: 88225

//header file included from both C and C++ files

#ifndef __cplusplus
#include <stdbool.h> // for C99 type bool
#endif

#ifdef __cplusplus
extern "C" {
#endif

void func(bool first, float min, float* state[6], float* err[6][6]);

#ifdef __cplusplus
} // extern "C"
#endif


// cpp file
#include "the_above_header.h"
#include <vector>

extern "C" void func(bool first, float min, float* state[6], float* err[6][6]);
{
    //uses vectors and classes and other C++ constructs
}

// c file
#include "the_above_header.h"

int main() {
    bool b;
    float f;
    float *s[6];
    float *err[6][6];
    func(b,f,s,err);
}

Upvotes: 1

Linuxios
Linuxios

Reputation: 35788

To call it in C, all you need to do is call it normally. Because you told the compiler to use the C calling conventions and ABI with extern "C", you can call it normally:

func(args);

To compiler, use this for the C++:

g++ -c -o myfunc.o myfunc.cpp

Then this for the C:

gcc -c -o main.o somec.c

Than link:

g++ -o main main.o myfunc.o

Make sure that the C++ header for the function uses ONLY C CONSTRUCTS. So include things like <vector> in the .cpp file instead.

Upvotes: 4

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272727

You call the function from C in the normal way. However, you need to wrap the extern "C" in an preprocessor macro to prevent the C compiler from seeing it:

#ifndef __cplusplus
extern "C"
#endif
void func(bool first, float min, float* state[6], float* err[6][6]);

Assuming you're working with GCC, then compile the C code with gcc, compile the C++ code with g++, and then link with g++.

Upvotes: 11

Related Questions