PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

76 Chapter 2 Storing and Retrieving Data
Using Other Useful File Functions
Numerous other file functions are useful from time to time. Some are described next.
Checking Whether a File Is There: file_exists()
If you want to check whether a file exists without actually opening it, you can use
file_exists(), as follows:
if (file_exists("$DOCUMENT_ROOT/../orders/orders.txt")) {
echo 'There are orders waiting to be processed.';
} else {
echo 'There are currently no orders.';
}
Determining How Big a File Is: filesize()
You can check the size of a file by using the filesize() function:
echo filesize(“$DOCUMENT_ROOT/../orders/orders.txt”);
It returns the size of a file in bytes and can be used in conjunction with fread() to read
a whole file (or some fraction of the file) at a time.You can even replace the entire original
script with the following:
$fp = fopen(“$DOCUMENT_ROOT/../orders/orders.txt”, ‘rb’);
echo nl2br(fread( $fp, filesize(“$DOCUMENT_ROOT/../orders/orders.txt” )));
fclose( $fp );
The nl2br() function converts the \n characters in the output to HTML line breaks
().
Deleting a File: unlink()
If you want to delete the order file after the orders have been processed, you can do so
by using unlink(). (There is no function called delete.) For example,
unlink(“$DOCUMENT_ROOT/../orders/orders.txt”);
This function returns false if the file could not be deleted.This situation typically
occurs if the permissions on the file are insufficient or if the file does not exist.
Navigating Inside a File: rewind(), fseek(), and ftell()
You can manipulate and discover the position of the file pointer inside a file by using
rewind(), fseek(), and ftell().
The rewind() function resets the file pointer to the beginning of the file.The
ftell() function reports how far into the file the pointer is in bytes. For example, you
can add the following lines to the bottom of the original script (before the fclose()
command):