test_write.c

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

int main(int argc, char **argv) {
  if (argc > 1) {
    int fd = open(argv[1], O_WRONLY);
    if(fd == -1) {
      printf("Unable to open the file\n");
      exit(1);
    }
    static struct flock lock;

    lock.l_type = F_WRLCK;
    lock.l_start = 0;
    lock.l_whence = SEEK_SET;
    lock.l_len = 0;
    lock.l_pid = getpid();

    int ret = fcntl(fd, F_SETLK, &lock);
    printf("Return value of fcntl:%d\n",ret);
    if(ret==0) {
      while (1) {
        scanf("%c", NULL);
      }
    } else {
      printf("error, ret:%d, errno:%d\n", ret, errno);
    }
  }
}