php版本比较函数version_compare()
php中比较php版本，一般用version_compare()函数，帮助文档见：http://php.net/manual/en/function.version-compare.php
用途：Compares two “PHP-standardized” version number strings。
语法：version_compare ( string $version1 , string $version2 [, string $operator ] )
具体描述：version_compare() compares two “PHP-standardized” version number strings. This is useful if you would like to write programs working only on some versions of PHP.
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 splits the results like if you were using explode(‘.’, $ver). 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.
其中第三个可选参数是比较符：
- If you specify the third optional operator argument, you can test for a particular relationship. The possible operators are: <, lt, <=, le, >, gt, >=, ge, ==, =, eq, !=, <>, ne respectively.
This parameter is case-sensitive, so values should be lowercase.
- 返回值：
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.
从下面的例子，就可以很好地说明version_compare的用法：
<?php
if (version_compare(PHP_VERSION, '6.0.0') >= 0) {
echo 'I am at least PHP version 6.0.0, my version: ' . PHP_VERSION . "n";
}
if (version_compare(PHP_VERSION, '5.3.0') >= 0) {
echo 'I am at least PHP version 5.3.0, my version: ' . PHP_VERSION . "n";
}
if (version_compare(PHP_VERSION, '5.0.0', '>=')) {
echo 'I am using PHP 5, my version: ' . PHP_VERSION . "n";
}
if (version_compare(PHP_VERSION, '5.0.0', '<')) {
echo 'I am using PHP 4, my version: ' . PHP_VERSION . "n";
}
?>
最近在nagios的图表监控插件pnp安装中遇到一个错误提示：Kohana requires PHP 5.2 or newer.查看页面源码，发现如下语句：
version_compare(PHP_VERSION, '5.2', '<') and exit('Kohana requires PHP 5.2 or newer.');
也就是版本不满足就退出。
strcmp()的字符串比较函数，也可以进行比较，但像下面这样，就会出现错误：
4.1.10与4.1.2比较
strcmp(“4.1.10″, “4.1.2″); 会返回-1 错误
version_compare(“4.1.10″. “4.1.2″); 就会返回1 正确
