dmalloc.c

/*
    dmalloc -l logfile -i 100 low
    gcc -DDMALLOC dmalloc.c -ocaesar -ldmalloc
*/

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

#ifdef DMALLOC
#include "dmalloc.h"
#endif

void usage(char *msg) {
    fprintf(stderr, "%s", msg);
    free(msg);
    return;
}

int main(int argc, char *argv[]) {
    if (argc != 3 && argc != 4) {
        /* the error message won't be more than 80 chars */
        char *errmsg = (char *)malloc(80);
        printf("%c", errmsg[90]);
        sprintf(
            errmsg,
            "Sorry %s, \nUsage: caesar secret_file keys_file [output_file]\n",
            getenv("USER")
        );
        usage(errmsg);
        free(errmsg);
        exit(EXIT_FAILURE);
    }

    // ...

    exit(EXIT_SUCCESS);
}