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 \n");
    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.

@BLUEPIXY: Those backslashes were the problem, now it works like a charm! Thanks a lot! — Alexandru Dinu
– Alexandru Dinu, Commented Oct 31, 2014 at 9:19
"didn't produce the expected output", it must have given you a compiler error, no? — Jens Gustedt
– Jens Gustedt, Commented Oct 31, 2014 at 9:39

2501 · Accepted Answer · 2014-10-31 09:19:05Z

1

Try in the form of:

-DSTR=\"MyString\"

answered Oct 31, 2014 at 9:19

2501

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1 Comment

It might be worth mentioning that this is a shell issue. If the command would be exec*()ed for example the back shlashes wouldn't be necessary.