lseek64

lseek64 - reposition 64-bit read/write file offset

#define _LARGEFILE64_SOURCE
#include <sys/types.h>
#include <unistd.h> I off64_t lseek64(int fd , off64_t offset , int whence );

The lseek(2) family of functions reposition the offset of the open file associated with the file descriptor fd to offset bytes relative to the start, current position, or end of the file, when whence has the value R SEEK_SET , R SEEK_CUR , or R SEEK_END , respectively.

For more details, return value, and errors, see lseek(2).

Four interfaces are available: lseek(2), R lseek64 (), llseek(2), and the raw system call _llseek(2).

lseek

Prototype:

 I off_t lseek(int  fd , off_t  offset , int  whence );

The library routine R lseek () uses the type R off_t . This is a 32-bit signed type on 32-bit architectures, unless one compiles with

 #define _FILE_OFFSET_BITS 64
 

in which case it is a 64-bit signed type.

lseek64

Prototype:

 I off64_t lseek64(int  fd , off64_t  offset , int  whence );

The library routine R lseek64 () uses a 64-bit type even when off_t is a 32-bit type. Its prototype (and the type R off64_t ) is available only when one compiles with

 #define _LARGEFILE64_SOURCE
 

The function R lseek64 () is available since glibc 2.1, and is defined to be an alias for R llseek ().

llseek

Prototype:

 I loff_t llseek(int  fd , loff_t  offset , int  whence );

The type loff_t is a 64-bit signed type. The library routine R llseek () is available in libc5 and glibc and works without special defines. Its prototype was given in <unistd.h> with libc5, but glibc does not provide a prototype. This is bad, since a prototype is needed. Users should add the above prototype, or something equivalent, to their own source. When users complained about data loss caused by a miscompilation of e2fsck(8), glibc 2.1.3 added the link-time warning "the \`llseek\' function may be dangerous; use \`lseek64\' instead." This makes this function unusable if one desires a warning-free compilation.

_llseek

All the above functions are implemented in terms of this system call. The prototype is:

 I int _llseek(int  fd , off_t  offset_hi , off_t  offset_lo ,
I loff_t * result , int  whence );

For more details, see llseek(2).

llseek(2), lseek(2), feature_test_macros(7)