php-取中间字符串

function getSubstr($str, $leftStr, $rightStr)
{
    $left = strpos($str, $leftStr);
    //echo '左边:'.$left;
    $right = strpos($str, $rightStr,$left);
    //echo '<br>右边:'.$right;
    if($left < 0 or $right < $left) return '';
    return substr($str, $left + strlen($leftStr), $right-$left-strlen($leftStr));
}