Re: small c problem

[Antti-Juhani Kaijanaho <gaia@iki.fi>]

On Thu, Jul 01, 1999 at 03:19:05PM +1200, Michael Beattie wrote:
>    char *rad_cmd;
>    rad_cmd = "number:";
>    What now?  i.e.  rad_cmd+freq_num to give rad_cmd = "number:444"
>    strcat()?

This is broken.  You should *never* assign a string constant to a non-const
variable!  Because if you subsequently try to mutate the string (and you
will) and you are lucky, you will be looking at a core dump.  Never, EVER,
mutate a constant!  Use -Wwrite-strings with gcc to catch these.

When you work with strings in C, you must *alwys* think about memory
management.  My solution to your problem uses malloc():

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
        int number = 444;
        char * string;
        const char * origstring = "number:";
        size_t string_len;

        string_len = 3 /* length of 444 */
                + strlen(origstring)
                + 1 /* for '\0' */;

        string = malloc(string_len);
        if (string == 0) abort(); /* Ugh.  Do better error handling. */

        snprintf(string, string_len, "%s%i", origstring, number);

        puts(string);

        free(string);

        return 0;
}

-- 
%%% Antti-Juhani Kaijanaho % gaia@iki.fi % http://www.iki.fi/gaia/ %%%

   "... memory leaks are quite acceptable in many applications ..."
    (Bjarne Stroustrup, The Design and Evolution of C++, page 220)