Header File 

io.h, sys\locking.h 

Category 

Input/output Routines 

Prototype 

int locking(int handle, int cmd, long length); 

Description 

Sets or resets file-sharing locks. 

locking provides an interface to the operating system file-sharing mechanism. The file to be locked or unlocked is the open file specified by handle. The region to be locked or unlocked starts at the current file position, and is length bytes long. 

Locks can be placed on arbitrary, nonoverlapping regions of any file. A program attempting to read or write into a locked region will retry the operation three times. If all three retries fail, the call fails with an error. 

The cmd specifies the action to be taken (the values are defined in sys\locking.h):

Return Value 

On successful operations, locking returns 0. Otherwise, it returns -1, and the global variable errno is set to one of the following values:

Example

#include <io.h>
#include <fcntl.h>
#include <process.h>
#include <share.h>
#include <stdio.h>
#include <sys\locking.h>
int main(void)
{
  int handle, status;
  long length;
  handle = sopen("c:\\autoexec.bat", O_RDONLY,SH_DENYNO);
  if (handle < 0) {
    printf("sopen failed\n");
    exit(1);
  }
  length = filelength(handle);
  status = locking(handle,LK_LOCK,length/2);
  if (status == 0)
    printf("lock succeeded\n");
  else
    perror("lock failed");
  status = locking(handle,LK_UNLCK,length/2);
  if (status == 0)
    printf("unlock succeeded\n");
  else
    perror("unlock failed");
  close(handle);
  return 0;
}

Portability