C：将__COUNTER__与字符串连接

Question

I want to stringify the __COUNTER__ and print it as a string not an integer, is that possible?

printf("%s\n", #__COUNTER__);

I have tried the following but it does not work

hello.c:6:19: error: stray ‘#’ in program
printf("%s\n",#__COUNTER__);

Answer 1

Yes, but it takes an indirection because you can't use the # operator outside of a macro.

#define STRINGIFY_2(a) #a
#define STRINGIFY(a) STRINGIFY_2(a)

printf("%s\n", STRINGIFY(__COUNTER__));

The double macro is required to expand __COUNTER__ , otherwise the result would be "__COUNTER__" .

If you don't want to reinvent that wheel, that's exactly what BOOST_PP_STRINGIZE does.

Answer 2

You have to stringify it with a preprocessor macro.

#define XSTR(s) STR(s)
#define STR(s) #s
printf("%s", XSTR(counter));