Moves a file pointer to the specified location.
| #include <io.h> | Required only for function declarations | |
| #include <stdio.h> |
long _lseek( int handle, long offset, int origin );
| handle | Handle referring to open file | |
| offset | Number of bytes from origin | |
| origin | Initial position |
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:
| Origin | Definition |
| SEEK_SET | Beginning of file |
| SEEK_CUR | Current position of file pointer |
| SEEK_END | End of file |
The _lseek function can be used to reposition the pointer anywhere in a file. The pointer can also be positioned beyond the end of the file. However, an attempt to position the pointer before the beginning of the file causes an error.
The _lseek function returns the offset, in bytes, of the new position from the beginning of the file. The function returns –1L to indicate an error and sets errno to one of the following values:
| Value | Meaning |
| EBADF | Invalid file handle |
| EINVAL | Invalid value for origin, or 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.
Standards:UNIX
16-Bit:DOS, QWIN, WIN, WIN DLL
32-Bit:DOS32X
Use _lseek for compatibility with ANSI naming conventions of non-ANSI functions. Use lseek and link with OLDNAMES.LIB for UNIX compatibility.
/* 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 );
}
Position for beginning of file seek = 0
Position for current position seek = 10
Position for end of file seek = 1183