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clinkage

Example of showing internal vs external linkage

I have the following which I'm trying to set up to show the difference between a variable with global scope vs one with file/program scope:

// scope.c
#include<stdio.h>

int main(void)
{
    printf("External: %d\n", external);
    printf("Internal (static): %d\n", internal); // should error
}

// scope_other.c
int external = 7;   // file scope, external linkage
static int internal = 6;   // file scope, internal linkage

And to compile with:

$ gcc scope.c scope_other.c -o scope && ./scope

But it seems like I'm missing something here to properly demonstrate the global vs static linkage. What would be the proper way to demonstrate this?

Solution

  • You need to have declarations of both variables in scope.c.

    Try adding extern int external, internal; in scope.c before the definition of main. This will fix the compiler errors you're undoubtedly seeing for both variables. But you will still get a linker error for internal only. If you comment out the line that prints internal, but leave the line that prints external alone, the program will compile, link and run.