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 #defines

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.