tlock.c

this gives details of the network programming

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>

/* File locking subroutines */

int lock_fd(int fd) {
  struct flock fl;

  fl.l_type=F_WRLCK;
  fl.l_start = 0;
  fl.l_whence=SEEK_SET;
  fl.l_len=0;
  return(fcntl(fd,F_SETLKW,&fl));
}


int unlock_fd( int fd) {
  struct flock fl;

  fl.l_type=F_WRLCK;
  fl.l_start = 0;
  fl.l_whence=SEEK_SET;
  fl.l_len=0;
  return(fcntl(fd,F_UNLCK,&fl));
}



main() {
  char c;
  FILE *f;

  f = fopen("foo","r+");
  if (f==NULL) {
    printf("Error - can't open the file\n");
    exit(1);
  }

  printf("Locking\n");
  if (lock_fd(fileno(f))>=0) {
    printf("GOT IT\n");
  } else {
    printf("CAN'T LOCK FILE\n");
    exit(1);
  }

  read(0,&c,1);
  printf("Unlocking\n");
  if (unlock_fd(fileno(f))>=0) {
    printf("DONE\n");
  } else {
    printf("CAN'T UNLOCK FILE\n");
    exit(1);
  }
  fclose(f);

}