How do I concatenate two strings in C?

Question

How do I add two strings?

I tried name = \"derp\" + \"herp\";, but I got an error:

Expression must have integral or enum type

Answer 1

David Heffernan explained the issue in his answer, and I wrote the improved code. See below.

A generic function

We can write a useful variadic function to concatenate any number of strings:

#include        // calloc
#include        // va_*
#include        // strlen, strcpy

char* concat(int count, ...)
{
    va_list ap;
    int i;

    // Find required length to store merged string
    int len = 1; // room for NULL
    va_start(ap, count);
    for(i=0 ; i

Usage

#include         // printf

void println(char *line)
{
    printf("%s\n", line);
}

int main(int argc, char* argv[])
{
    char *str;

    str = concat(0);             println(str); free(str);
    str = concat(1,"a");         println(str); free(str);
    str = concat(2,"a","b");     println(str); free(str);
    str = concat(3,"a","b","c"); println(str); free(str);

    return 0;
}

Output:

  // Empty line
a
ab
abc

Clean-up

Note that you should free up the allocated memory when it becomes unneeded to avoid memory leaks:

char *str = concat(2,"a","b");
println(str);
free(str);