Website Development Tutorial 3

Outline Getting data from the user using forms Sending data from a form to a PHP program Writing the data to a file for permanent storage Reading data back from a file

File reading and writing Useful for data sets too small for a database Enables code to read and write to a file Typical session might follow these steps Open the file for read/write Read in the contents Close the file (if only reading data) Perform operations of the file contents Write the results Close the file W3schools Tutorial

The fopen() function is used to open files in PHP. <?php $file=fopen(“guestbook.txt","r"); ?>

If you can’t open the file <?php $file=fopen(“guestbook.txt","r") or exit("Unable to open file!"); ?>

Closing the file <?php $file = fopen(“guestbook.txt","r"); //some code to be executed fclose($file); ?>

read a file line by line, until the end of file is reached: <?php $file = fopen(“guestbook.txt", "r") or exit("Unable to open file!"); //Output a line of the file until the end is reached while(!feof($file)) { echo fgets($file). " "; } fclose($file); ?>

Any writing to a file is done with the use of “fwrite()” or “fputs()” functions, which both use a file pointer and a string to perform the writing:

General Example $fd = fopen($filename, “r+”) or die(“Can’t open file $filename”); $fstring = fread($fd, filesize($filename)); $fout = fwrite($fd,$fstring); fclose($fd);

File open fopen() Have to assign the result to a variable Usually $fd (file descriptor) or $fp (file pointer) fopen() doesn’t return anything useful if unsuccessful (from a test point of view) so use die() to test for failure Six modes for opening “r” – read only “r+” – read and write if the file exists already “w” – write only “w+” – write and read even if the file doesn’t exist “a” – write only to the end of the file “a+” – read and write to the end of the file

File read fread() Takes a file-pointer and file size (in bytes) Most common way to send size is to use the filesize() function $fstring = fread($fd, filesize($filename)); Notice it is filesize($filename), not filesize($fd) – a common mistake Useful for turning a file’s contents into a string, can then use all the string functions to slice and dice the string Can also send the information to an array through use of file() and explode() functions – more later on these

File write Used for writing a string to a file Expects a file pointer and a string Returns the number of characters saved $fout = fwrite($fp, $string); if ($fout != strlen($fstring)) { echo “file write failed”; }

Important note on writing! If we use modes “w” and “w+” we will overwrite all the data in the file Which means that, EVERYTHING WILL BE LOST! If you want to add to beginning of file use “r+” If you want to add to end of file use “a+”

File close Does what it says on the tin fclose($fd); Not essential, PHP close all files at end of script, but its good house keeping