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!
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++.
-c option in the GCC manuals, and what "linking" is about. Otherwise, no answer you could get here will make sense.
.so, .dll, etc.). Because this is GCC, I think that it is probably Linux, and if it isen't, GCC on other platforms still uses .so. (Mac uses it anyway, on Windows you need a Cygwin-like layer).
ifdef __cplusplus?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.
-c option tells the compiler to only compile your code to intermediate object code files (.o) which can then be linked together into an executable by excluding the -c option. Object files allow you to combine C and C++, and impose some separation into different parts of the project. They also allow you to compile only small parts of your code, which is crucial to large projects and systems like make.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.
//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);
}
{ }), or is it declared in the header (i.e., ending with);)? If it's the former, you need to write another header file that omits theextern "C"and{ }part, and use that for the C part of your program.