c環境下Json字符串的解析
對於Json字符串，最常見的方式就是一個一個的鍵值對被一個大的Obect包裹着，但是往往由於實際項目需要json字符串不可能保持最簡單的形式來進行數據傳輸。
以最近一個小項目爲例：
從手機客戶端組織數據，形成Json字符串的主要形式有如下幾種：
1. char *xjson = "[{\"TotalNum\":123},{\"Tvstate\":2},{\"ProgrameId\":014000789},{\"request\":1004}]";
2.char *xjson = "{\"TotalNum\":\"123\",\"name\":\"mao\",\"request\":1004}";
3.char *xjson = "{\"ToIndex\":\"99\",\"FromIndex\":\"0\",\"request\":\"0\"}";
4.char *xjson = "{\"array\":[{\"TotalNum\": 123,\"Tvstate\": \"2\"}],\"request\": 44}";
5.char *xjson = "{\"array\":[{\"TotalNum\": 123},{\"Tvstate\": \"2\"}],\"request\": \"44\"}";
6.char *xjson = "{\"TvSate\":0,\"FavMark\":64,\"FavGroupId\":\"\",\"array\":[{\"ProgrameId\": \"4334\"},{\"ProgrameId\":4334}],\"TotalNum\":3,\"request\":1004}";
7.char *xjson = "{\"array\":[{\"data\":\"M040\"},{\"uuid\":\"860806027379485-38:BC:1A:87:E0:26\"}],\"request\":\"998\"}";
8.char *xjson = "{\"request\":1004}";
需要在機頂盒端接收到手機客戶端發送過來的json字符串數據，並且將其解析出來存放到各自對應的已經實現定義好的結構體中。
大致的過程就是：
APK -------發送Json字符串給------>服務器端------解析json字符串到------>C結構體
那麼具體的需求就是：
在服務器端的解析函數必須能夠適配解析不同的json字符串。在不知道每一個json字符串的鍵值對的情況下，取出該json字符串的鍵值，存放在c結構體中，並且將這些結構體以鏈表的形式存放在內存中。
在c語言環境下有一個開源的cJSON庫，其中封裝好了一些列對json數據進行操作的函數。
cJSON結構體定義如下：
typedefstruct cJSON {
structcJSON *next,*prev;
struct cJSON *child;
int type;
char * valuestring;
int valueint;
double valuedouble;
char *string;
}cJSON;
其中type取值共有7中，分別是：
#define cJSON_False 0
#define cJSON_True 1
#define cJSON_NULL 2
#define cJSON_Number 3
#define cJSON_String 4
#define cJSON_Array 5
#define cJSON_Object 6
考慮到我們在客戶端組織起來的json字符串主要由Number、String、Array、Object組成，因此採用多重嵌套swicth進行解析。當然也可以使用遞歸進行解析，但是由於遞歸在項目開發中特別是嵌入式開發中一般不建議使用，所以這次並沒有採用遞歸的方法進行解析。
具體的解析代碼
其中涉及到的主要函數爲：
解析的入口函數:parse_cjson_to_json_root（）
解析子json結構體爲Array的函數：parse_json_sub_type_array();
解析子json結構體爲Object的函數：parse_json_sub_type_object();
解析子json結構體爲Number和String的函數：parse_json_sub_type_others();
主要代碼如下：
<pre name="code" class="html">#include <stdio.h>
#include <string.h>
#include "usifext.h"
#include "json_parser.h"
#include "cJSON.h"
#include "gs_os.h"
void parse_json_sub_type_others(cJSON** psub, json_node_info** tag_node, json_root_info** proot_node, json_node_info** tag_point,
json_attr_info** tag_attr_node, int type)
{
int text_int = 0;
char *text_string = "";
(*tag_node) = (json_node_info *)malloc(sizeof(json_node_info));
memset((*tag_node)->tag_name, 0, sizeof((*tag_node)->tag_name));
memset((*tag_node)->tag_text, 0, sizeof((*tag_node)->tag_text));
char *tag = (*psub)->string;
if (cJSON_Number == type)
{
text_int = (*psub)->valueint;
}
else
{
text_string = (*psub)->valuestring;
}
if (strcmp(tag, JSON_HEADER_CONTROL_TAG) != 0)
{
strcpy((*tag_node)->tag_name, tag);
if (cJSON_Number == type)
{
ITOA((*tag_node)->tag_text, text_int);
}
else
{
strcpy((*tag_node)->tag_text, text_string);
}
(*tag_node)->next = NULL;
if ((*proot_node)->next == NULL)
{
(*proot_node)->next = (*tag_node);
(*tag_point) = (*tag_node);
}
else
{
(*tag_point)->next = (*tag_node);
(*tag_point) = (*tag_node);
}
}
else
{
(*tag_attr_node) = (json_attr_info*)malloc(sizeof(json_attr_info));
memset((*tag_attr_node)->name, 0, sizeof((*tag_attr_node)->name));
memset((*tag_attr_node)->value, 0, sizeof((*tag_attr_node)->value));
strcpy((*tag_attr_node)->name, tag);
if (cJSON_Number == type)
{
ITOA((*tag_attr_node)->value, text_int);
}
else
{
strcpy((*tag_attr_node)->value, text_string);
}
(*proot_node)->attr_list = (*tag_attr_node);
}
}
void parse_json_sub_type_array(cJSON** psub, json_node_info** tag_node, json_root_info** proot_node, json_node_info** tag_point,
json_attr_info** tag_attr_node)
{
int j = 0;
for (j = 0; j < cJSON_GetArraySize((*psub)); j++)
{
cJSON *psub_sub = cJSON_GetArrayItem((*psub), j);
if (psub_sub->type == cJSON_Object)
{
parse_json_sub_type_obj(&psub_sub, tag_node, proot_node, tag_point, tag_attr_node);
}
}
}
void parse_json_sub_type_obj(cJSON** psub, json_node_info** tag_node, json_root_info** proot_node, json_node_info** tag_point,
json_attr_info** tag_attr_node)
{
int j = 0;
for (j = 0; j < cJSON_GetArraySize((*psub)); j++)
{
cJSON *psub_sub = cJSON_GetArrayItem((*psub), j);
parse_json_sub_type_others(&psub_sub, tag_node, proot_node, tag_point, tag_attr_node, psub_sub->type);
}
}
int parse_cjson_to_json_root(cJSON *pjson, json_root_info *proot_node)
{
int i = 0;
int size = 0;
json_node_info* tag_node;
json_attr_info* tag_attr_node;
json_node_info* tag_point = NULL;
if (NULL == proot_node)
{
return -1;
}
if (NULL == pjson)
{
return -1;
}
(proot_node)->next = NULL;
size = cJSON_GetArraySize(pjson);
for (i = 0; i < size; i++)
{
cJSON *psub = cJSON_GetArrayItem(pjson, i);
switch (psub->type)
{
case cJSON_Array:
parse_json_sub_type_array(&psub, &tag_node, &proot_node, &tag_point, &tag_attr_node);
break;
case cJSON_Object:
parse_json_sub_type_obj(&psub, &tag_node, &proot_node, &tag_point, &tag_attr_node);
break;
case cJSON_String:
case cJSON_Number:
parse_json_sub_type_others(&psub, &tag_node, &proot_node, &tag_point, &tag_attr_node, psub->type);
break;
default:
return -1;
}
}
return 0;
}int ITOA(char * str, unsigned long val)
{
char *p;
char *first_dig;
<span style="white-space:pre"> </span>char temp;
unsigned t_val;
int len = 0;
p = str;
first_dig = p;
do
{
t_val = (unsigned)(val % 0x0a);
val /= 0x0a;
*p++ = (char)(t_val + '0');
len++;
}
while (val > 0);
*p-- = '\0';
do
{
temp = *p;
*p = *first_dig;
*first_dig = temp;
--p;
++first_dig;
}
while (first_dig < p);
return len;
}
</pre><pre name="code" class="html">採用遞歸的方式更加簡單，主要函數和代碼如下：int parse_json(cJSON * pJson,xml_root_info *proot_node)
{
xml_node_info* tag_node;
xml_attr_info* tag_attr_node;
xml_node_info* tag_point = NULL;
tag_node = (xml_node_info *) malloc(sizeof(xml_node_info));
memset(tag_node->tag_name,0,sizeof(tag_node->tag_name));
memset(tag_node->tag_text,0,sizeof(tag_node->tag_text));
tag_attr_node = (xml_attr_info*) malloc(sizeof(xml_attr_info));
memset(tag_attr_node->name,0,sizeof(tag_attr_node->name));
memset(tag_attr_node->value,0,sizeof(tag_attr_node->value));
tag_point = (xml_node_info *) malloc(sizeof(xml_node_info));
if(NULL == pJson)
{
return -1;
}
printf(" pJson->type :%d\n", pJson->type);
switch(pJson->type)
{
case cJSON_False :
{
char *value_string = pJson->string;
int value_int = pJson->valueint;
strcpy(tag_node->tag_name, value_string);
//ITOA(tag_attr_node->value, value_int);
}
break;
case cJSON_True :
{
char *value_string = pJson->string;
int value_int = pJson->valueint;
strcpy(tag_node->tag_name, value_string);
//ITOA(tag_attr_node->value, value_int);
}
break;
case cJSON_NULL :
{
printf("%s : NULL\n", pJson->string);
}
break;
case cJSON_Number :
{
char *value_string = pJson->string;
int value_int = pJson->valueint;
if(strcmp(value_string, "request") != 0)
{
strcpy(tag_node->tag_name, value_string);
itoa(value_int, tag_node->tag_text, 10);
tag_node->next = NULL;
if(count == 0)
{
proot_node->next = tag_node;
tag_point = tag_node;
count++;
}
else
{
tag_point = (proot_node)->next;
while(NULL != tag_point->next)
{
printf("up循環遍歷裏面\n");
tag_point = tag_point->next;
printf("down循環遍歷裏面\n");
}
tag_point->next = tag_node;
tag_point = tag_node;
}
}
else
{
strcpy(tag_attr_node->name, value_string);
itoa(value_int, tag_attr_node->value, 10);
proot_node->attr_list = tag_attr_node;
//proot_node->next=NULL;
}
}
break;
case cJSON_String :
{
char *value_string = pJson->string;
char *pJsonString = pJson->valuestring;
if(strcmp(value_string, "request") != 0)
{
strcpy(tag_node->tag_name, value_string);
strcpy(tag_node->tag_text, pJsonString);
tag_node->next = NULL;
if(count == 0)
{
proot_node->next = tag_node;
tag_point = tag_node;
count++;
printf("count_01:%d\n", count);
}
else
{
tag_point = (proot_node)->next;
while(NULL != tag_point->next)
{
printf("up循環遍歷裏面\n");
tag_point = tag_point->next;
printf("down循環遍歷裏面\n");
}
tag_point->next = tag_node;
tag_point = tag_node;
}
}
else
{
strcpy(tag_attr_node->name, value_string);
strcpy(tag_attr_node->value, pJsonString);
proot_node->attr_list = tag_attr_node;
}
}
break;
case cJSON_Array :
case cJSON_Object :
{
int iSize = cJSON_GetArraySize(pJson);
int i = 0;
printf("%s\n", NULL == pJson->string ? "" : pJson->string);
for(i = 0; i < iSize; i++)
{
cJSON * pSub = cJSON_GetArrayItem(pJson, i);
parse_json(pSub, proot_node);
}
}
break;
default :
return -1;
break;
}
}