c - Replace #define X macro value with another one specified in compilation command

Question

Given the following code:

#include <stdio.h>

#ifndef STR
    #define STR "HELLO"
#endif

int main() {
    printf(STR "WORLD 
");
    return 0;
}

which says: if STR was not defined, then define it to be "HELLO", so the output will be

HELLO WORLD

How can I modify the value of STR when compiling using gcc?

I've tried

gcc -Wall program.c -DSTR="HI" -o program

but it didn't produce the expected output.

Answer 1

Try in the form of:

-DSTR="MyString"