PHP Fatal error: Call to undefined function json_decode()

　　php：5.5，操作系统：ubuntu13.10

　　网站文本编辑器使用的是ueditor，测试上传图片显示后台配置项未成功加载，上传插件不能正常使用。

　　查阅了ueditor的文档，有关运行测试那里先访问ueditor/controller.php，提示出错，再访问ueditor/php/controller.php?action=config，提示PHP Fatal error: Call to undefined function json_decode()。原因是json相关函数为定义。

　　查看php官方文档，从php5.2就开始支持json扩展，可能是意外删掉了json组件，故重新安装。

　　sudo apt-get install php5-json

　　sudo service nginx restart

　　sudo php5-fpm restart

　　问题解决

　　如果php版本太低可以升级到5.2以后，不想重新安装php的话，可以自定义函数 json_encode 和 json_decode

function json_encode( $data ) {
    if( is_array($data) || is_object($data) ) {
        $islist = is_array($data) && ( empty($data) || array_keys($data) === range(0,count($data)-1) );

        if( $islist ) {
            $json = ‘[‘ . implode(‘,‘, array_map(‘__json_encode‘, $data) ) . ‘]‘;
        } else {
            $items = Array();
            foreach( $data as $key => $value ) {
                $items[] = __json_encode("$key") . ‘:‘ . __json_encode($value);
            }
            $json = ‘{‘ . implode(‘,‘, $items) . ‘}‘;
        }
    } elseif( is_string($data) ) {
        # Escape non-printable or Non-ASCII characters.
        # I also put the \\ character first, as suggested in comments on the ‘addclashes‘ page.
        $string = ‘"‘ . addcslashes($data, "\\\"\n\r\t/" . chr(8) . chr(12)) . ‘"‘;
        $json    = ‘‘;
        $len    = strlen($string);
        # Convert UTF-8 to Hexadecimal Codepoints.
        for( $i = 0; $i < $len; $i++ ) {

            $char = $string[$i];
            $c1 = ord($char);

            # Single byte;
            if( $c1 <128 ) {
            $json .= ($c1 > 31) ? $char : sprintf("\\u%04x", $c1);
            continue;
            }

            # Double byte
            $c2 = ord($string[++$i]);
            if ( ($c1 & 32) === 0 ) {
            $json .= sprintf("\\u%04x", ($c1 - 192) * 64 + $c2 - 128);
            continue;
            }

                # Triple
                $c3 = ord($string[++$i]);
                if( ($c1 & 16) === 0 ) {
                $json .= sprintf("\\u%04x", (($c1 - 224) <<12) + (($c2 - 128) << 6) + ($c3 - 128));
                continue;
        }

        # Quadruple
        $c4 = ord($string[++$i]);
            if( ($c1 & 8 ) === 0 ) {
                    $u = (($c1 & 15) << 2) + (($c2>>4) & 3) - 1;

                    $w1 = (54<<10) + ($u<<6) + (($c2 & 15) << 2) + (($c3>>4) & 3);
                    $w2 = (55<<10) + (($c3 & 15)<<6) + ($c4-128);
                    $json .= sprintf("\\u%04x\\u%04x", $w1, $w2);
                    }
                    }
                    } else {
                    # int, floats, bools, null
                    $json = strtolower(var_export( $data, true ));
                    }
                    return $json;
    }
    function json_decode($json)
    {
        $comment = false;
        $out = ‘$x=‘;

        for ($i=0; $i<strlen($json); $i++)
        {
        if (!$comment)
            {
            if (($json[$i] == ‘{‘) || ($json[$i] == ‘[‘)) $out .= ‘ array(‘;
                    else if (($json[$i] == ‘}‘) || ($json[$i] == ‘]‘)) $out .= ‘)‘;
                    else if ($json[$i] == ‘:‘) $out .= ‘=>‘;
                    else $out .= $json[$i];
        }
        else $out .= $json[$i];

if ($json[$i] == ‘"‘ && $json[($i-1)]!="\\") $comment = !$comment;
    }

        eval($out . ‘;‘);
    return $x;
    }