Make c++ macro2 containt quoted body of macro1

Question

I'm trying to make some kind of a simple system that calculates the number of builds, including this info in .rc file (for windows) and met the problem. Here it is:

#define QUOTE(s) #s
#define A       0,0,0,1
#define A_STR   QUOTE(A)

Expanding of A_STR: "A" but not "0,0,0,1" as I expected.

Well, I need A_STR to be a string representation of A (that's what windres expects to see in .rc file), but I can't find the way to do this.

I've already tried smth like #define A_STR #A but it simply expands to #0,0,0,1.

I also tried using qmake like this: DEFINES *= A_STR="<here-is-how-I-get-version>" but gcc gets it without quotes and I've got the same problem.

Answer 1

When a C preprocessor macro is expanded, its parameters are expanded to their literal arguments, so s would be expanded to A when your QUOTE(s) taking argument A is expanded. Normally, after this expansion is complete, the expanded text is then scanned again to expand any macros embedded therein, so this would cause the A to expand to 0,0,0,1. However, when the stringification operator # is used to stringify the following text, that stringification happens first, so the following text never gets a chance to be expanded, thus you get stringified "A" as the final expansion of A_STR.

This problem is normally solved by introducing a second level of indirection, which gives the initial macro argument a second chance to expand:

#define QUOTE2(A) #A
#define QUOTE(A) QUOTE2(A)

However, this would not actually work for your case, because in the first-level expansion the A would expand to 0,0,0,1, which would be taken as four arguments to QUOTE2(), and thus would be rejected as an invalid macro call.

You can solve this with variadic macro arguments and __VA_ARGS__:

#define QUOTE2(...) #__VA_ARGS__
#define QUOTE(...) QUOTE2(__VA_ARGS__)