Section 8.3 open and create calls


Demonstrate the cp like program which copies the contents of one file to another.

#include <fcntl.h>
#include <stdarg.h>
#include <stdio.h>
#include <sys/syscall.h>
#include <unistd.h>

#define PERMS 0666 /* RW for owner, group and others */

#define BUFSIZ 1024

void merror(char *, ...);

int main(int argc, char *argv[]) {
    int f1, f2, n;
    char buf[BUFSIZ];

    if (argc != 3)
        merror("Usage: prog: from to");

    if ((f1 = open(argv[1], O_RDONLY, 0)) == -1)
        merror("prog: can't open %s", argv[1]);
    if ((f2 = creat(argv[2], PERMS)) == -1)
        merror("prog: can't create %s, mode %03o", argv[2], PERMS);

    while ((n = read(f1, buf, BUFSIZ)) > 0)
        if (write(f2, buf, n) != n)
            merror("prog: write error on file %s", argv[2]);

    return 0;

void merror(char *fmt, ...) {
    va_list args;
    va_start(args, fmt);
    fprintf(stderr, "error: ");
    vfprintf(stderr, fmt, args);
    fprintf(stderr, "\n");