Handling files with PHP4 - Part1

Opening and Closing Files

File handling usually involves three steps. The file is opened, then put to use (whether reading or writing), and finally closed. All files should be opened before they are used, and closed when you've finished with them. Some of the functions do this automatically, but it's important to get into the habit from the beginning.

To open a file, you need to know what you're going to be doing with the file (reading or writing), and of course the name of the file. The PHP function to do this is fopen, and is used as follows:

int fopen (string filename, string mode [, int use_include_path])

Mode can be any of the following:

The fopen function returns an integer called the file handle, which is used in the other functions we'll look at later, or false if the open failed for any reason. This means we can use it in a safe way that deals with errors, as follows:

<?	
$filename = "/home/ian/hiddensecrets.txt";
if (!($fp = fopen ($filename, "w"))) {
print "Error - could not open the file $filename";
}
else {
	// process the file...
}
?>

Be careful with Windows pathnames. If you use a backslash (\), you'll need to escape it. You can also use forward slashes (/) for Windows pathnames.

<?
$filename = "c:\\images\\lion.gif";
if (!($fp = fopen ($filename, "rb"))) {
	print "Error - could not open the file $filename";
}
else {
	// process the file...
}
?>

PHP also usefully allows you to read files on remote servers. By beginning the filename with http:// the server connects to the remote server via HTTP 1.0 in order to open the file. Similarly, prepending ftp:// opens an ftp connection. The ftp server must support passive ftp, otherwise the connection will fail. Note that early versions of PHP4 (before version 4.0.5) did not support HTTP redirects, which means you'd need to put the trailing slash at the end of the filename.

The optional parameter at the end of the function indicates whether PHP should search the directories in the the include path (set in php.ini). It can be set to '1' or TRUE, otherwise it defaults to FALSE.

<?
$filename = "http://lionsandtigers.co.za/images/tiger.jpg";
if (!($fp = fopen ($filename, "rb"))) {
	print "Error - could not open the file $filename";
}
else {
	// process the file...
}
?>

Closing a file is easy - just call the fclose function with file handler passed to you when the file was opened. Closing files may seem pointless, especially as you're unlikely to notice a difference when testing with small scripts like these. Leaving files open unecessarily just puts extra load on your systems, and is bound to bite you if you're working on larger systems.

bool fclose (int fp)

<?	
$filename = "/home/ian/hiddensecrets.txt";
if (!($fp = fopen ($filename, "w"))) {
	print "Error - could not open the file $filename";
}
else {
	// process the file...
	fclose($fp);
}
?>

Although fclose() returns true or false, most code doesn't check for the possible failure of this operation unless it's absolutely critical to know. Besides, the vast majority of failures occur when opening a file, (invalid filenames or paths etc.), while the kinds of errors that can cause your successfully opened file not to close, (disk failures etc.), are not the kind of thing your code can do much about.

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