How to use C++ function from header in C?

Question

I'm writing my thesis and I have problem with using C++ function in C code. I searched solution and I found a lot of them, but it didn't work anyway. Please explain it to me one more time.

To be quick I have something like below and after gcc main.c -o main I get undefined reference to 'cppfun'

cpp.h:

#pragma once

#ifdef __cplusplus
 extern "C" {
#endi

    void cppfun();

#ifdef __cplusplus
 }
#endif

cpp.cpp:

#include <stdio.h>
#include "cpp.h"

void cppfun()
{
    printf("cpp_fun");
}

main.c:

#include <stdio.h>
#indlude "cpp.h"

int main(int argc, char *argv[])
{
    cppfun();
    return 0;
}

Answer 1

When you combine C and C++, you should compile the translation unit containing the main function, as C++. Not opposite. This is a FAQ.

An undefined reference is usually because you haven't linked in the translation unit where the missing thing is. Your stated build command is

gcc main.c -o main

while it should be e.g.

gcc -c main.c
g++ -c cpp.cpp
g++ cpp.o main.o -o main

except as mentioned, the main translation unit should be in C++.