C预处理多遍

Question

I'm a littlebit confused about the behaviour of preprocessing in c.

    #include <stdio.h>

#define myMacro anotherMacro

#define anotherMacro 6

int main()
{
    int dummy = myMacro;
    printf("dummy = %d", dummy);

    return 0;
}

in the above code snippet, the result will 6. however the the macro expansion in the initial pass will replace "myMacro" by "anotherMacro". this is means that preprocessor will make a second pass to resolve "anotherMacro" to value 6.

Answer 1

The preprocessor will make a second pass. He works through the source file line per line.

So if he reaches the first define

#define myMacro anotherMacro

he will replace all occurrences of myMacro with the string anotherMacro .

The file will look like this after the line is handled:

#include <stdio.h>

#define anotherMacro 6

int main()
{
    int dummy = anotherMacro;
    printf("dummy = %d", dummy);

    return 0;
}

Now the preprocessor could continue with the next #define
and replace every anotherMacro with the text 6