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PHP的json_encode使用分析说明

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Release： 2016-05-25 16:40:11
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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,那什么才是标准的json格式？代码如下:

{a : 'abc'} {'a' : 'abc'} {a : "abc"} {"a" : "abc"}
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谁都知道,只有第四种才是标准的json格式,我这么做,代码如下:

$ret_json='{"%s":"%s"}';echo json_encode($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？

实例代码如下:

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;//开源代码phprm.com 
    }   
    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;
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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:

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:
/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 <= 0) {//如果len小于0 说明出错。如果用json_encode处理GBK的编码，就会在这里挂掉。 
    if (utf16) { 
            efree(utf16); 
    } 
    if (len < 0) { 
            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 < len) 
{ 
    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 << 4) - 1)]); 
                            us >>= 4; 
                            smart_str_appendc(buf, digits[us & ((1 << 4) - 1)]); 
                            us >>= 4; 
                            smart_str_appendc(buf, digits[us & ((1 << 4) - 1)]); 
                            us >>= 4; 
                            smart_str_appendc(buf, digits[us & ((1 << 4) - 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:
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, '}'); 
    } 
}
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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).


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