Inspect a Preprocessor Macro Expansion

Before high-level C code is compiled into assembly instructions or binary machine code, it must pass through the preprocessor stage. The preprocessor handles directive lines starting with #, resolving header inclusions (#include) and performing macro text expansions (#define) before the actual compiler runs. This challenge is a hands-on detour into this very first stage of the C compilation pipeline.

The four stages of the C compilation pipeline. This challenge focuses on the first one.

When you write a macro like #define GREETING "Hello, expanded world!\n", the compiler does not see the word GREETING. The preprocessor replaces it before the compiler proper even starts. The -E flag tells gcc to stop after that stage, so you can inspect the expanded source.

Your task is to:

1. Create a workspace directory named ~/exercise.
2. Inside ~/exercise, create a file named preprocessor.c with the following contents:

#include <stdio.h>

#define GREETING "Hello, expanded world!\n"

int main(void) {
    printf("%s", GREETING);
    return 0;
}

3. Change into ~/exercise and run gcc -E preprocessor.c.
4. Locate the line where the GREETING macro was expanded inside the printf call.