_lseek, _lseeki64

Move a file pointer to the specified location.

long _lseek( int handle, long offset, int origin );

__int64 _lseeki64( int handle, __int64 offset, int origin );

For additional compatibility information, see Compatibility in the Introduction.

Libraries

Return Value

_lseek returns the offset, in bytes, of the new position from the beginning of the file. _lseeki64 returns the offset in a 64-bit integer. The function returns  –1L to indicate an error and sets errno either to EBADF, meaning the file handle is invalid, or to EINVAL, meaning the value for origin is invalid or the position specified by offset is before the beginning of the file. On devices incapable of seeking (such as terminals and printers), the return value is undefined.

Parameters

handle

Handle referring to open file

offset

Number of bytes from origin

origin

Initial position

Remarks

The _lseek function moves the file pointer associated with handle to a new location that is offset bytes from origin. The next operation on the file occurs at the new location. The origin argument must be one of the following constants, which are defined in STDIO.H:

SEEK_SET

Beginning of file

SEEK_CUR

Current position of file pointer

SEEK_END

End of file

You can use _lseek to reposition the pointer anywhere in a file or beyond the end of the file.

Example

/* LSEEK.C: This program first opens a file named LSEEK.C.
 * It then uses _lseek to find the beginning of the file,
 * to find the current position in the file, and to find
 * the end of the file.
 */

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

void main( void )
{
   int fh;
   long pos;               /* Position of file pointer */
   char buffer[10];

   fh = _open( "lseek.c", _O_RDONLY );

   /* Seek the beginning of the file: */
   pos = _lseek( fh, 0L, SEEK_SET );
   if( pos == -1L )
      perror( "_lseek to beginning failed" );
   else
      printf( "Position for beginning of file seek = %ld\n", pos );

   /* Move file pointer a little */
    _read( fh, buffer, 10 );

   /* Find current position: */
   pos = _lseek( fh, 0L, SEEK_CUR );
   if( pos == -1L )
      perror( "_lseek to current position failed" );
   else
      printf( "Position for current position seek = %ld\n", pos );

   /* Set the end of the file: */
   pos = _lseek( fh, 0L, SEEK_END );
   if( pos == -1L )
      perror( "_lseek to end failed" );
   else
      printf( "Position for end of file seek = %ld\n", pos );

   _close( fh );
}

Output

Position for beginning of file seek = 0
Position for current position seek = 10
Position for end of file seek = 1207

Low-Level I/O Routines

See Also   fseek, _tell