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cmacrosc-preprocessorstringification

What does #x inside a C macro mean?

For example I have a macro:

#define PRINT(int) printf(#int "%d\n",int)

I'm somewhat aware of the outcome. But how come #int represent the whole thing?

I'm somewhat forget this detail. Can anybody kindly give me a hint?

Thanks!

Solution

  • In this context (applied to a parameter reference in a macro definition), the pound sign means to expand this parameter to the literal text of the argument that was passed to the macro.

    In this case, if you call PRINT(5) the macro expansion will be printf("5" "%d\n", 5); which will print 5 5; not very useful; however if you call PRINT(5+5) the macro expansion will be printf("5+5" "%d\n", 5+5); which will print 5+5 10, a little less trivial.

    This very example is explained in this tutorial on the C preprocessor (which, incidentally, is the first Google hit for c macro pound sign).