When printing off source code there is a handy function that will parse the code and produce nice looking syntax highlighted code. There are actually two functions you can use. The highlight_string() function takes a string as a parameter and will print the highlighted code. The highlight_file() function takes a file name as a parameter, the contents of which are printed off with highlighted syntax. For now I will concentrate on the highlight_string() function, but the output of these two functions is the same.

To use the highlight_string() function just pass it a string. The following code:

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highlight_string('<?php 
function checkslash($slashes_string){
  if (get_magic_quotes_gpc()==1) {
    return $slashes_string;
  }else{
    return addslashes($slashes_string);
  };
};
?>');

Will produce the following output:

How the code is highlighted depends on your version of PHP. In all cases the code is highlighted using HTML, but it is the syntax that changes. In PHP 4 the main HTML tag used is <font>. Running the code in PHP 5 produces output that consists of the <span> tag. Both versions of PHP also wrap the output in the <code> tag to preserve the line breaking of the code.

Finally, both of these functions (since PHP 4.2.0) will now accept a second parameter. This is a boolean value that tells the function to either print the highlighted string out (false, which is the default) or to simply return the string (true).