rndgen1.c

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

/* generate a text file with random combinations of 4 characters
   from a, b, c, d on each line */
/* created for testing performance here: http://askubuntu.com/a/339182/67132 */
/* compilation: make rndgen1 */
/* detailed compilation: make rndgen1 CC=gcc CFLAGS="-W -Wall -pedantic" */

#define NLINES 200000000    /* number of output lines */
#define CHPLINE 4       /* characters per line */
#define PROGNAME "rndgen1"  /* program name */
#define NPOSIB 4        /* output character possibilities */
#define FCHAR 'a'       /* first output character possibility */

void errexit(const char *msg)
{
        fprintf(stderr, "%s: %s\n", PROGNAME, msg);
        exit(EXIT_FAILURE);
}

int main(int argc, char *argv[])
{
        int i, j;
        FILE *fout;

        if(argc < 2) errexit("Too little arguments - You must specify an output file.");
        if((fout = fopen(argv[1], "w")) == NULL) errexit("Error opening output file");
        srand(time(NULL));

        for(i = 0; i < NLINES; i++) {
                for(j = 0; j < CHPLINE; j++) {
                        if(putc(FCHAR + rand() % NPOSIB, fout) == EOF) {
                errexit("Error writting to file.");
            }
                }
                if(putc('\n', fout) == EOF) errexit("Error writting to file.");
        }

        fclose(fout);
        return EXIT_SUCCESS;
}