*** UNIX MANUAL PAGE BROWSER ***

lseek(2) System Calls Manual lseek(2) NAME lseek - Moves read-write file offset SYNOPSIS #include <sys/types.h> #include <unistd.h> off_t lseek ( int filedes, off_t offset, int whence ); STANDARDS Interfaces documented on this reference page conform to industry stan- dards as follows: lseek(): POSIX.1, XPG4 Refer to the standards(5) reference page for more information about in- dustry standards and associated tags. PARAMETERS Specifies a file descriptor obtained from a successful open() or fc- ntl() function. Specifies a value, in bytes, that is used in conjunc- tion with the whence parameter to set the file pointer. A negative value causes seeking in the reverse direction. The resulting file posi- tion may also be negative. Specifies how to interpret the offset pa- rameter in setting the file pointer associated with the filedes parame- ter. Values for the whence parameter are: Sets the file pointer to the value of the offset parameter. Sets the file pointer to its current location plus the value of the offset parameter. Sets the file pointer to the size of the file plus the value of the offset parameter. DESCRIPTION The lseek() function sets the file offset for the open file specified by the filedes parameter. The whence parameter determines how the off- set is to be interpreted. The lseek() function allows the file offset to be set beyond the end of existing data in the file. If data is later written at this point, subsequently reading data in the gap returns bytes with the value 0 (zero) until data is actually written into the gap. By itself, the lseek() function does not extend the size of the file. RETURN VALUES Upon successful completion, the resulting pointer location, measured in bytes from the beginning of the file, is returned. If the lseek() func- tion fails, the file offset remains unchanged, a value of (off_t) - 1 is returned, and errno is set to indicate the error. ERRORS If the lseek() function fails, the file offset remains unchanged and errno may be set to one of the following values: The filedes parameter is not an open file descriptor. The whence parameter is an invalid value or the resulting file offset would be invalid. The filedes para- meter is associated with a pipe (FIFO), a socket, or a multiplexed spe- cial file. RELATED INFORMATION Functions: fcntl(2), fseek(3), open(2), read(2), write(2) Standards: standards(5) delim off lseek(2)