PHP | fseek( ) Function (original) (raw)

Last Updated : 13 Jun, 2018

The fseek() function in PHP is an inbuilt function which is used to seek in an open file. It moves the file pointer from its current position to a new position, forward or backward specified by the number of bytes. The file and the offset are sent as parameters to the fseek() function and it returns 0 on success, or -1 on failure.

Syntax:

int fseek ( file,file, file,offset, $whence)

Parameters: The fseek() function in PHP accepts three parameters as described below.

$file: It is a mandatory parameter which specifies the file.
$offset: It is a mandatory parameter which specifies the new position of the pointer. It is measured in bytes from the beginning of the file.
$whence: It is an optional parameter which can have the following possible values-
- SEEK_SET: It sets position equal to offset.
- SEEK_CUR: It sets position to current location plus offset.
- SEEK_END: It sets position to EOF plus offset. To move to a position before EOF, the offset must be a negative value.

Return Value: It returns 0 on success, or -1 on failure.

Exceptions:

Seeking past EOF(end of file) generates an error.
If a file is open in append (a or a+) mode, then any data written to the file will always be appended, regardless of the file position, and the result of calling fseek() will be undefined.
Not all streams support seeking. For those that do not support seeking, forward seeking from the current position is accomplished by reading and discarding data; other forms of seeking will fail.

Below programs illustrate the fseek() function in PHP:

Program 1: In the below program the file named gfg.txt contains the following content:

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<?php

$myfile = fopen ( "gfg.txt" , "w" );

fgets ( $myfile );

echo fseek ( $myfile , 0);

fclose( $myfile );

?>

Output:

Program 2: In the below program the file named gfg.txt contains the following content: