1、PHP加密解密

PHP加密和解密函数可以用来加密一些有用的字符串存放在数据库里，并且通过可逆解密字符串，该函数使用了base64和MD5加密和解密。

function encryptDecrypt($key, $string, $decrypt){

    if($decrypt){

        $decrypted = rtrim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, md5($key), base64_decode($string), MCRYPT_MODE_CBC, md5(md5($key))), "12");

        return $decrypted;

    }else{

        $encrypted = base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, md5($key), $string, MCRYPT_MODE_CBC, md5(md5($key))));

        return $encrypted;

    }

}

2、PHP生成随机字符串

function generateRandomString($length = 10) {

    $characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

    $randomString = '';

    for ($i = 0; $i < $length; $i++) {

        $randomString .= $characters[rand(0, strlen($characters) - 1)];

    }

    return $randomString;

}

3、PHP获取文件扩展名（后缀）

function getExtension($filename){

  $myext = substr($filename, strrpos($filename, '.'));

  return str_replace('.','',$myext);

}

4、PHP获取文件大小并格式化

function formatSize($size) {

    $sizes = array(" Bytes", " KB", " MB", " GB", " TB", " PB", " EB", " ZB", " YB");

    if ($size == 0) { 

        return('n/a'); 

    } else {

      return (round($size/pow(1024, ($i = floor(log($size, 1024)))), 2) . $sizes[$i]); 

    }

}

5、PHP替换标签字符

function stringParser($string,$replacer){

    $result = str_replace(array_keys($replacer), array_values($replacer),$string);

    return $result;

}