php截取字符串Ａ－Ｂ

 $str = '{"res":"{\"type\":\"remove\",\"title\":\"10692467199507114（验证码）\",\"packgename\":\"com.android.mms\",\"time\":\"2020-10-21 12:47:53\",\"content\":\"【YY语音】您的验证码为：822124，10分钟内有效。如非本人操作，请忽略。\",\"id\":\"1390\"}"}
    ';
    $str = json_decode($str,true);
    $content = $str['res'];
    $content = json_decode($content,true);
    $content = $content['content'];
    
    
    $content = cut("：","，",$content);
    
    
    print_r($str);
    echo "<br>";
    echo "====================<br>";
    echo "截取后<br>";
    echo "====================<br>";
    echo  $content;

    function cut($begin,$end,$str){
          $b = mb_strpos($str,$begin) + mb_strlen($begin);
          $e = mb_strpos($str,$end) - $b;
          return mb_substr($str,$b,$e);
    }