本文章来给大家介绍json_encode使用分析，兴趣了解php源码的朋友可尝试参考哦。
json的优点就不说了，
有个习惯，我在输出json的时候，喜欢用 sprintf 拼成json格式，
前两天被朋友说不标准，必须要用json_encode生成的才是标准的json格式，我当然很郁闷啦，
用了这么多年了，刚知道 这样做不标准，既然说我不标准，那上面才是标准的json格式？
 代码如下 复制代码
{a : 'abc'} {'a' : 'abc'} {a : abc} {a : abc}
那都知道，只有第四种才是标准的json格式。
我这么做
 代码如下 复制代码
$ret_json='{%s:%s}';
echo json_encode($ret_json,a,abc);
必然也符合标准。
既然如此，那我就要刨根问底，json_encode生成的json格式究竟有什么不同？
上代码
 代码如下 复制代码
static php_function(json_encode)
{
        zval *parameter;
        smart_str buf = {0};
        long options = 0;
if (zend_parse_parameters(zend_num_args() tsrmls_cc, z|l, ¶meter, &options) == failure) {
                return;
        }
json_g(error_code) = php_json_error_none;
php_json_encode(&buf, parameter, options tsrmls_cc);
zval_stringl(return_value, buf.c, buf.len, 1);
smart_str_free(&buf);
}
json_g(error_code) = php_json_error_none;
是定义的json错误，该错误可以通过json_last_error函数获取，你用过吗？反正我没用过。
php_json_encode是主要的操作
 代码如下 复制代码
php_json_api void php_json_encode(smart_str *buf, zval *val, int options tsrmls_dc) /* {{{ */
{
        switch (z_type_p(val))
        {
                case is_null:
                        smart_str_appendl(buf, null, 4); //输出null
                        break;
case is_bool:
                        if (z_bval_p(val)) {
                                smart_str_appendl(buf, true, 4);//输出true
                        } else {
                                smart_str_appendl(buf, false, 5);//输出false
                        }
                        break;
case is_long:
                        smart_str_append_long(buf, z_lval_p(val));//输出长整形的值
                        break;
case is_double:
                        {
                                char *d = null;
                                int len;
                                double dbl = z_dval_p(val);
if (!zend_isinf(dbl) && !zend_isnan(dbl)) {//非无穷尽
                                        len = spprintf(&d, 0, %.*k, (int) eg(precision), dbl);
                                        smart_str_appendl(buf, d, len);
                                        efree(d);
                                } else {
                                        php_error_docref(null tsrmls_cc, e_warning, double %.9g does not conform to the json spec, encoded as 0, dbl);
                                        smart_str_appendc(buf, '0');
                                }
                       }
                        break;
case is_string://字符串
                        json_escape_string(buf, z_strval_p(val), z_strlen_p(val), options tsrmls_cc);
                        break;
case is_array://数组和对象
                case is_object:
                        json_encode_array(buf, &val, options tsrmls_cc);
                        break;
default:
                        php_error_docref(null tsrmls_cc, e_warning, type is unsupported, encoded as null);
                        smart_str_appendl(buf, null, 4);
                        break;
        }
return;
}
很明显，根据不同的类型，会有相应的case。
最复杂的是 字符串 、数组 、对象这三种类型，数组和对象是同一种操作。
先看看字符串吧，很长，注释直接写在代码里。
 代码如下 复制代码
/options应该是5.3版本之后才支持的，由以下常量组成的二进制掩码： json_hex_quot, json_hex_tag, json_hex_amp, json_hex_apos, json_numeric_check, json_pretty_print, json_unescaped_slashes, json_force_object, json_unescaped_unicode.虽然我没用过。。。
static void json_escape_string(smart_str *buf, char *s, int len, int options tsrmls_dc) /* {{{ */
{
        int pos = 0;
        unsigned short us;
        unsigned short *utf16;
if (len == 0) {//如果长度为0，则直接返回 双引号
                smart_str_appendl(buf, , 2);
                return;
        }
if (options & php_json_numeric_check) {//检测是否为0-9的数字，如果是数字，那么就会直接把数据作为long或double类型返回。
                double d;
                int type;
                long p;
if ((type = is_numeric_string(s, len, &p, &d, 0)) != 0) {
                        if (type == is_long) {
                                smart_str_append_long(buf, p);
                        } else if (type == is_double) {
                                if (!zend_isinf(d) && !zend_isnan(d)) {
                                        char *tmp;
                                        int l = spprintf(&tmp, 0, %.*k, (int) eg(precision), d);
                                        smart_str_appendl(buf, tmp, l);
                                        efree(tmp);
                                } else {
                                        php_error_docref(null tsrmls_cc, e_warning, double %.9g does not conform to the json spec, encoded as 0, d);
                                        smart_str_appendc(buf, '0');
                                }
                        }
                        return;
                }
}
utf16 = (unsigned short *) safe_emalloc(len, sizeof(unsigned short), 0);
        len = utf8_to_utf16(utf16, s, len); //这里会对你输入的值一次处理转成对应的dec码，比如1是49，a是97这样的，保存到utf16中。
        if (len                 if (utf16) {
                        efree(utf16);
                }
                if (len                         json_g(error_code) = php_json_error_utf8;
                        if (!pg(display_errors)) {
                                php_error_docref(null tsrmls_cc, e_warning, invalid utf-8 sequence in argument);
                        }
                        smart_str_appendl(buf, null, 4);
                } else {
                        smart_str_appendl(buf, , 2);
                }
                return;
        }
smart_str_appendc(buf, ''); //输入
//下面这一段代码就是将一些特殊字符转义如 双引号，反斜线等等
        while (pos         {
                us = utf16[pos++];
switch (us)
                {
                        case '':
                                if (options & php_json_hex_quot) {
                                        smart_str_appendl(buf, \u0022, 6);
                                } else {
                                        smart_str_appendl(buf, \, 2);
                                }
                                break;
case '\':
                                smart_str_appendl(buf, \\, 2);
                                break;
case '/':
                                smart_str_appendl(buf, \/, 2);
                                break;
case 'b':
                                smart_str_appendl(buf, \b, 2);
                                break;
case 'f':
                                smart_str_appendl(buf, \f, 2);
                                break;
case 'n':
                                smart_str_appendl(buf, \n, 2);
                                break;
case 'r':
                                smart_str_appendl(buf, \r, 2);
                                break;
case 't':
                                smart_str_appendl(buf, \t, 2);
                                break;
case '                                if (options & php_json_hex_tag) {
                                        smart_str_appendl(buf, \u003c, 6);
                                } else {
                                        smart_str_appendc(buf, '                                }
                                break;
case '>':
                                if (options & php_json_hex_tag) {
                                        smart_str_appendl(buf, \u003e, 6);
                                } else {
                                        smart_str_appendc(buf, '>');
}
                                break;
case '&':
                                if (options & php_json_hex_amp) {
                                        smart_str_appendl(buf, \u0026, 6);
                                } else {
                                        smart_str_appendc(buf, '&');
                                }
                                break;
case ''':
                                if (options & php_json_hex_apos) {
                                        smart_str_appendl(buf, \u0027, 6);
                                } else {
                                        smart_str_appendc(buf, ''');
                                }
                                break;
default: //一直到这里，没有特殊字符就会把值append到buf中
                                if (us >= ' ' && (us & 127) == us) {
                                        smart_str_appendc(buf, (unsigned char) us);
                                } else {
                                        smart_str_appendl(buf, \u, 2);
                                        us = reverse16(us);
smart_str_appendc(buf, digits[us & ((1                                         us >>= 4;
                                        smart_str_appendc(buf, digits[us & ((1                                         us >>= 4;
                                        smart_str_appendc(buf, digits[us & ((1                                         us >>= 4;
                                        smart_str_appendc(buf, digits[us & ((1                                 }
                                break;
                }
        }
        smart_str_appendc(buf, ''); //结束 双引号。
        efree(utf16);
}
再来看看数组和对象，也很简单，
 代码如下 复制代码
static void json_encode_array(smart_str *buf, zval **val, int options tsrmls_dc) /* {{{ */
{
        int i, r;
        hashtable *myht;
if (z_type_pp(val) == is_array) {
                myht = hash_of(*val);
                r = (options & php_json_force_object) ? php_json_output_object : json_determine_array_type(val tsrmls_cc);
        } else {
                myht = z_objprop_pp(val);
                r = php_json_output_object;
        }
if (myht && myht->napplycount > 1) {
                php_error_docref(null tsrmls_cc, e_warning, recursion detected);
                smart_str_appendl(buf, null, 4);
                return;
        }
//开始标签
        if (r == php_json_output_array) {
                smart_str_appendc(buf, '[');
        } else {
                smart_str_appendc(buf, '{');
        }
i = myht ? zend_hash_num_elements(myht) : 0;
if (i > 0)
        {
                char *key;
                zval **data;
                ulong index;
                uint key_len;
                hashposition pos;
                hashtable *tmp_ht;
                int need_comma = 0;
zend_hash_internal_pointer_reset_ex(myht, &pos);
//便利哈希表
                for (;; zend_hash_move_forward_ex(myht, &pos)) {
                        i = zend_hash_get_current_key_ex(myht, &key, &key_len, &index, 0, &pos);
                        if (i == hash_key_non_existant)
                                break;
if (zend_hash_get_current_data_ex(myht, (void **) &data, &pos) == success) {
                                tmp_ht = hash_of(*data);
                                if (tmp_ht) {
                                        tmp_ht->napplycount++;
                                }
if (r == php_json_output_array) {
                                        if (need_comma) {
                                                smart_str_appendc(buf, ',');
                                        } else {
                                                need_comma = 1;
                                        }
//将值append到 buf中
                                        php_json_encode(buf, *data, options tsrmls_cc);
                                } else if (r == php_json_output_object) {
                                        if (i == hash_key_is_string) {
                                                if (key[0] == '' && z_type_pp(val) == is_object) {
                                                        /* skip protected and private members. */
                                                        if (tmp_ht) {
                                                                tmp_ht->napplycount--;
                                                        }
                                                        continue;
                                                }
if (need_comma) {
                                                        smart_str_appendc(buf, ',');
                                                } else {
                                                        need_comma = 1;
                                                }
json_escape_string(buf, key, key_len - 1, options & ~php_json_numeric_check tsrmls_cc);
                                                smart_str_appendc(buf, ':');
php_json_encode(buf, *data, options tsrmls_cc);
                                        } else {
                                                if (need_comma) {
                                                        smart_str_appendc(buf, ',');
                                                } else {
                                                        need_comma = 1;
                                                }
smart_str_appendc(buf, '');
                                                smart_str_append_long(buf, (long) index);
                                                smart_str_appendc(buf, '');
                                                smart_str_appendc(buf, ':');
php_json_encode(buf, *data, options tsrmls_cc);
                                        }
                                }
if (tmp_ht) {
                                        tmp_ht->napplycount--;
                                }
                        }
                }
        }
//结束标签
        if (r == php_json_output_array) {
                smart_str_appendc(buf, ']');
        } else {
                smart_str_appendc(buf, '}');
        }
}
通过简单分析，证明了一个问题，跟我上面用sprintf的方法其实是一样的，都是拼接字符串，
而且 为了性能，更应该鼓励用sprintf来拼接json格式，
因为 json_encode会进行很多 循环操作，而且所消耗的性能是线性的 o(n^2)。
http://www.bkjia.com/phpjc/629905.htmlwww.bkjia.comtruehttp://www.bkjia.com/phpjc/629905.htmltecharticle本文章来给大家介绍json_encode使用分析，兴趣了解php源码的朋友可尝试参考哦。 json的优点就不说了， 有个习惯，我在输出json的时候，喜欢...