php json_decode失败，返回null

　　在使用json_decode之前，一定得保证字符串是utf-8编码，而执行json_decode失败的原因有很多，罗列如下：

      1）编码不对；

      2）字符串格式不对；

      3）字符串格式对，但是有异常字符；

      为了解决这个问题，可以考虑保证编码对上，json字符串可以正常解析，虽然说的简单，但是有许多工作要做，现在上一种万能解决方案，不啰嗦，看代码：

    

// 获得编码，如果有其它编码，完善下面的编码列表即可
$encode = mb_detect_encoding($json_info, array("ASCII","UTF-8","GB2312","GBK","BIG5","EUC-CN"));
// 将字符串转为utf-8编码
 $tmp = iconv($encode,"UTF-8//IGNORE", $json_info);

// reject overly long 2 byte sequences, as well as characters above U+10000 and replace with ?
 $tmp = preg_replace('/[x00-x08x10x0Bx0Cx0E-x19x7F]'.
                     '|[x00-x7F][x80-xBF]+'.
                      '|([xC0xC1]|[xF0-xFF])[x80-xBF]*'.
                       '|[xC2-xDF]((?![x80-xBF])|[x80-xBF]{2,})'.
                        '|[xE0-xEF](([x80-xBF](?![x80-xBF]))|(?![x80-xBF]{2})|[x80-xBF]{3,})/S',
                         '?', $tmp);

// reject overly long 3 byte sequences and UTF-16 surrogates and replace with ?
 $tmp = preg_replace('/xE0[x80-x9F][x80-xBF]'.
                     '|xED[xA0-xBF][x80-xBF]/S','?', $tmp);
// decode
$result_data = json_decode($tmp,true);

参考地址：

https://magp.ie/2011/01/06/remove-non-utf8-characters-from-string-with-php/

http://blog.sina.com.cn/s/blog_65db99840101fxzv.html

https://segmentfault.com/a/1190000006154011