Mastering Go - Second Edition

The C code

The relevant C code can be found in the willUseGo.c source file, which will be presented in two parts. The first part of willUseGo.c is next:

#include <stdio.h> 
#include "usedByC.h" 
 
int main(int argc, char **argv) { 
    GoInt x = 12; 
    GoInt y = 23; 
 
    printf("About to call a Go function!\n"); 
    PrintMessage(); 

If you already know C, you will understand why you need to include usedByC.h; this is the way the C code knows about the available functions of a library.

The second part of the C program is next:

    GoInt p = Multiply(x,y); 
    printf("Product: %d\n",(int)p); 
    printf("It worked!\n"); 
    return 0; 
} 

The GoInt p variable is needed for getting an integer value from a Go function, which is converted to a C integer using the (int) p notation. ...