php将带单位的文件大小字符串转换成字节数

例如：将5M或者400K这样的字符串转换成字节数字显示

function StringSizeToBytes($Size){
 
    $Unit = strtolower($Size);
    $Unit = preg_replace('/[^a-z]/', '', $Unit);
 
    $Value = intval(preg_replace('/[^0-9]/', '', $Size));
 
    $Units = array('b'=>0, 'kb'=>1, 'mb'=>2, 'gb'=>3, 'tb'=>4);
    $Exponent = isset($Units[$Unit]) ? $Units[$Unit] : 0;
 
    return ($Value * pow(1024, $Exponent));            
}
// Example usage:
// Check if a file is bigger than 10 MB
 
if (filesize('example.zip') > StringSizeToBytes('10 MB')){
    print 'File is to big !';
}
else {
    print 'File is okay';
}