duplicate a c-string on stack

            char tmp[strlen(src)+1]; // I guess strlen(src) must be known at compile time
            strcpy(tmp,src);

On stack, the array capacity must be determined before runtime.

If you want to declare an array whose capacity is determined at run time, you must use heap. http://stackoverflow.com/questions/252782/strdup-what-does-it-do-in-c explains strdup()