lseek

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Header File

io.h

Category

Input/output Routines

Prototype

long lseek(int handle, long offset, int fromwhere); 
__int64 _lseeki64(int handle, __int64 offset, int fromwhere); 

Description

Moves file pointer.

lseek sets the file pointer associated with the handle to a new position offset bytes beyond the file location given by fromwhere. fromwhere must be one of the following symbolic constants (defined in io.h):

SEEK_CUR	Current file pointer position
SEEK_END	End-of-file
SEEK_SET	File beginning

Return Value

lseek returns the offset of the pointer's new position measured in bytes from the beginning of the file. lseek returns -1L on error, and the global variable errno is set to one of the following values:

EBADF	Bad file handle
EINVAL	Invalid argument
ESPIPE	Illegal seek on device

On devices incapable of seeking (such as terminals and printers), the return value is undefined.

Example

#include <sys\stat.h>
#include <string.h>
#include <stdio.h>
#include <fcntl.h>
#include <io.h>
int main(void)
{
    int handle;
    char msg[] = "This is a test";
    char ch;
    /* create a file */
    handle = open("TEST.$$$", O_CREAT | O_RDWR, S_IREAD | S_IWRITE);
    /* write some data to the file */
    write(handle, msg, strlen(msg));
    /* seek to the beginning of the file */
    lseek(handle, 0L, SEEK_SET);
    /* reads chars from the file until we hit EOF */
    do
    {
       read(handle, &ch, 1);
       printf("%c", ch);
    }  while (!eof(handle));
    close(handle);
    return 0;
}
 

Portability

POSIX	Win32	ANSI C	ANSI C++
+	+