Concatenate int to string using C Preprocessor

Question

I'm trying to figure out how I can concatenate a #define 'd int to a #define 'd string using the C Preprocessor. My compiler is GCC 4.1 on CentOS 5. The solution should also work for MinGW.

I'd like to append a version number onto a string, but the only way I can get it to work is to make a copy of the version number defines as strings.

The closest thing I could find was a method of quoting macro arguments, but it doesn't work for #define s

This is does not work.

#define MAJOR_VER 2
#define MINOR_VER 6
#define MY_FILE "/home/user/.myapp" #MAJOR_VER #MINOR_VER

It doesn't work without the # s either because the values are numbers and it would expand to "/home/user/.myapp" 2 6 , which isn't valid C .

This does work, but I don't like having copies of the version defines because I do need them as numbers as well.

#define MAJOR_VER 2
#define MINOR_VER 6
#define MAJOR_VER_STR "2"
#define MINOR_VER_STR "6"
#define MY_FILE "/home/user/.myapp" MAJOR_VER_STRING MINOR_VER_STRING

Answer 1

Classical C preprocessor question....

#define STR_HELPER(x) #x
#define STR(x) STR_HELPER(x)

#define MAJOR_VER 2
#define MINOR_VER 6
#define MY_FILE "/home/user/.myapp" STR(MAJOR_VER) STR(MINOR_VER)

The extra level of indirection will allow the preprocessor to expand the macros before they are converted to strings.

Answer 2

A working way is to write MY_FILE as a parametric macro:

#define MY_FILE(x,y) "/home..." #x #y

EDIT: As noted by "Lindydancer", this solution doesn't expand macros in arguments. A more general solution is:

#define MY_FILE_(x,y) "/home..." #x #y
#define MY_FILE(x,y) MY_FILE_(x,y)

Answer 3

You can do that with BOOST_PP_STRINGIZE :

#define MAJOR_VER 2
#define MINOR_VER 6
#define MY_FILE "/home/user/.myapp" BOOST_PP_STRINGIZE(MAJOR_VER) BOOST_PP_STRINGIZE(MINOR_VER)