$json_str = '{"key":"value"}';
var_dump(json_decode($json_str));//结果正常
$json_str = '{"key":"\\value"}';
var_dump(json_decode($json_str));//结果是null
echo json_last_error();//结果是4,对应JSON_ERROR_SYNTAX(意思是Syntax error)
$json_str = '{"key":"\\\value"}';
var_dump(json_decode($json_str));//终于把\显示出来了
$json_str = '{"key":"\\\\value"}';
var_dump(json_decode($json_str));//居然结果和三个\是一样的
$json_str = '{"key":"\\\\\value"}';
var_dump(json_decode($json_str));//null
$json_str = '{"key":"\\\\\\value"}';
var_dump(json_decode($json_str));//null
$json_str = '{"key":"\\\\\\\value"}';
var_dump(json_decode($json_str));//足足输入了7个\,才可以正常显示两个\
$json_str = '{"key":"\\\\\\\\value"}';
var_dump(json_decode($json_str));//结果和7个\一样
$json_str = '{"key":"\\\\\\\\\value"}';
var_dump(json_decode($json_str));//又到了null了
$json_str = '{"key":"\\\\\\\\\\value"}';
var_dump(json_decode($json_str));//null
$json_str = '{"key":"\\\\\\\\\\\value"}';
var_dump(json_decode($json_str));//11个\,显示三个\
$json_str = '{"key":"\\\\\\\\\\\\value"}';
var_dump(json_decode($json_str));//12个\,显示三个\
//.......