Section 21.5. Cross-Platform Code 5: Checking the PHP Version with phpversion( ) and version_compare( )

21.5. Cross-Platform Code 5: Checking the PHP Version with phpversion( ) and version_compare( )

If you only want your script to work on certain versions of PHP, there are two functions just for you: phpversion( ) and version_compare( ). The first takes no parameters, and returns a string containing the version number of the current version of PHP. The second takes two parameters, which should be two version strings of the type returned by phpversion( ), and returns -1 if the first version is lower than the second, 0 if they are the same, and 1 if the first version is higher than the second.

     $CurrentVer = phpversion( )     print "Current PHP version: $CurrentVer\n";     switch (version_compare($CurrentVer, '5.0.0') {             case -1:                     print "You're running an old PHP: $CurrentVer\n";                     break;             case 0:                     print "You are running PHP 5\n";                     break;             case 1:                     print "You are running a version of PHP after 5.0.0: $CurrentVer\n";     } 

That should output "Current PHP version: <your version here>", then either "You are running PHP 5" or "You are running a version of PHP after 5.0.0: <your version here>". Internally, this is actually a very advanced function, as it automatically distinguishes between development code, alpha, beta, and release candidate versions, and it allows you to check an arbitrary amount of version numbers. For example: 5.0.0b1 < 5.0.0RC1-dev < 5.0.0RC1 < 5.0.0RC2 < 5.0.0 < 5.0.0.0.0.0.1 < 5.0.1, etc.

What's more, there's nothing to say you have to use the PHP version for your checks. For example, if you are distributing your PHP application and want to check that each file is the correct version, you can compare your own version strings using this function as long as they match the same format as PHP.

Instead of using the function phpversion( ), you can also use the constant PHP_VERSION. Many people still prefer to use the function, however, as its behavior is clearerthe choice is yours, as they both do exactly the same thing.