Php returns NULL using json_decode

Php5.2 and later comes with the json_decode function, but the format requirements for json text strings are very strict. The return value obtained by using this function is NULL. the return value obtained by using the json_last_error () function is JSON_ERROR_SYNTAX (Syntax error ). You can troubleshoot the error in the following ways. 1. json strings must contain $ output = str_replace ("'",' "', $ output); 2. the json string must be UTF-8 encoded $ output = iconv ('gbk', 'utf8', $ output); 3. there cannot be redundant commas, for example, [,], replace with regular expressions, preg_replace ('/, \ s * ([\]}])/m',' $1 ', $ output)