version_compare compares two "PHP-standardized" version number strings.
The function first replaces _, - and + with a dot . in the version strings and also inserts dots . before and after any non number so that for example '4.3.2RC1' becomes '4.3.2.RC.1'. Then it compares the parts starting from left to right. If a part contains special version strings these are handled in the following order: any string not found in this list < dev < alpha = a < beta = b < RC = rc < # < pl = p. This way not only versions with different levels like '4.1' and '4.1.2' can be compared but also any PHP specific version containing development state.
First version number.
Second version number.
An optional operator. The possible operators are: <, lt, <=, le, >, gt, >=, ge, ==, =, eq, !=, <>, ne respectively.
This parameter is case-sensitive, values should be lowercase.
By default, version_compare returns -1 if the first version is lower than the second, 0 if they are equal, and 1 if the second is lower.
When using the optional operator argument, the function will return true if the relationship is the one specified by the operator, false otherwise.
The PHP_VERSION constant holds current PHP version.
Note that pre-release versions, such as 5.3.0-dev, are considered lower than their final release counterparts (like 5.3.0).
Special version strings such as alpha and beta are case sensitive. Version strings from arbitrary sources that do not adhere to the PHP standard may need to be lowercased via strtolower before calling version_compare.