1、json資料格式和json-c簡介[1]

JSON(JavaScriptObject Notation) 是一種輕量級的資料交換格式。易於人閱讀和編寫。同時也易於機器解析和生成。

JSON採用完全獨立於語言的文字格式，但是也使用了類似於C語言家族的習慣（包括C,C++, C#, Java, JavaScript, Perl, Python等）。這些特性使JSON成為理想的資料交換語言。

跟XML相比，JSON的優勢在於格式簡潔短小，特別是在處理大量複雜資料的時候，這個優勢便顯得非常突出。從各瀏覽器的支援來看，JSON解決了因不同瀏覽器對XMLDOM解析方式不同而引起的問題。

JSON

就json來說，由於結構比較簡單，不用庫也是可以的。

但json-c提供了超出json範圍的一些功能，實際上完成了資料序列化和反序列化，資料的儲存和檢索，資料物件化等功能。還是非常有使用價值的。

2、json-c庫的安裝：

參考於https://github.com/json-c/json-c/wiki[2]

[1]下載json-c並解壓：

進入[2]網址並下載最新的json-c壓縮包：

選擇下載（截止到2017/9/19日這個是最新的）。

解壓壓縮包：#tar -xzvf json-c-0.9.tar.gz

進入資料夾：#cdjson-c-0.9

[2]編譯並安裝（注意許可權，許可權不夠請使用sudo）：

#./configure–prefix=/some/install/path

/some/install/path 是你的json-c安裝路徑，我使用的是/usr/include

再執行

#make

#makecheck

#makeinstall

進行編譯安裝

[3]檢視是否安裝成功：

#cd/usr/include/json

進入該資料夾檢視裡面有json的相關檔案，說明安裝成功了。

3、json-c的使用

json-c庫函式使用起來較為簡單：

申請json物件（以infor_object為例）：

structjson_object *infor_object = NULL;

infor_object= json_object_new_object();

釋放json物件：

json_object_put(infor_object);

新增json值型別到陣列中

json_object_array_add(array_object,json_object_new_int(256));

json_object_array_add(array_object,json_object_new_int(257));

json_object_array_add(array_object,json_object_new_int(258));

json_object_object_add(para_object,"DeviceId", json_object_new_string("sn_iso_9000"));

json_object_object_add(para_object,"MacAddr", json_object_new_string("AA:BB:CC:DD:EE:FF"));

json_object_object_add(para_object,"Visible", json_object_new_int(1));

新增json名稱和值到json物件集合中

json_object_object_add(infor_object,"method", json_object_new_string("GetSystemInfo"));

json_object_object_add(infor_object,"param", para_object);

json_object_object_add(infor_object,"id", json_object_new_string("101"));

新增陣列集合到json物件中

json_object_object_add(infor_object,"array", array_object);

下面是例項：

#include <stdio.h>  
#include <json/json.h>  
#include <stdlib.h>

void test_jsonc()  
{  
  
    struct json_object *infor_object = NULL;  
    infor_object = json_object_new_object();  
    if (NULL == infor_object)  
    {  
        printf("new json object failed.\n");  
        return;  
    }  
  
    struct json_object *para_object = NULL;  
    para_object = json_object_new_object();  
    if (NULL == para_object)  
    {  
        json_object_put(infor_object);//free  
        printf("new json object failed.\n");  
        return;  
    }  
  
    struct json_object *array_object = NULL;  
    array_object = json_object_new_array();  
    if (NULL == array_object)  
    {  
        json_object_put(infor_object);//free  
        json_object_put(para_object);//free  
        printf("new json object failed.\n");  
        return;  
    }  
  
    /*新增json值型別到陣列中*/  
    json_object_array_add(array_object, json_object_new_int(256));  
    json_object_array_add(array_object, json_object_new_int(257));  
    json_object_array_add(array_object, json_object_new_int(258));  
  
    json_object_object_add(para_object, "DeviceId", json_object_new_string("sn_iso_9000"));  
    json_object_object_add(para_object, "MacAddr", json_object_new_string("AA:BB:CC:DD:EE:FF"));  
    json_object_object_add(para_object, "Visible", json_object_new_int(1));  
  
    /*新增json名稱和值到json物件集合中*/  
    json_object_object_add(infor_object, "method", json_object_new_string("GetSystemInfo"));  
    json_object_object_add(infor_object, "param", para_object);  
    json_object_object_add(infor_object, "id", json_object_new_string("101"));  
  
    /*新增陣列集合到json物件中*/  
    json_object_object_add(infor_object, "array", array_object);  
    json_object_to_file("1.json",infor_object); 
    
    struct json_object *result_object = NULL;  
    
    result_object =  json_object_object_get(infor_object, "method");  
    printf("-----------result_object method ---------------------------\n");  
    printf("%s\n", json_object_to_json_string(result_object));  
    printf("-----------result_object method---------------------------\n");  
  
    result_object =  json_object_object_get(infor_object, "param");  
    printf("-----------result_object param ---------------------------\n");  
    printf("%s\n", json_object_to_json_string(result_object));  
    printf("-----------result_object param---------------------------\n");  
  
    result_object =  json_object_object_get(infor_object, "array");  
    printf("-----------result_object  array---------------------------\n");  
    printf("%s\n", json_object_to_json_string(result_object));  
    printf("-----------result_object array---------------------------\n");  
  
    int i;  
    for(i = 0; i < json_object_array_length(result_object); i++) {  
      struct json_object *obj = json_object_array_get_idx(result_object, i);  
      printf("\t[%d]=%s\n", i, json_object_to_json_string(obj));  
    }  

    struct json_object *file_object = NULL;  
    unsigned int filesize = 0;
    FILE *fp;  
    fp = fopen("1.json", "r");  
    fseek(fp, 0L, SEEK_END);  
    filesize = ftell(fp);    
    printf("filesize is %d \n",filesize);
    fclose(fp);

    FILE *fp2;  
    char *file;
    fp2 = fopen("1.json", "r");
    file = (char *)malloc(filesize + 1);
    fseek(fp2, SEEK_SET, 0);
    fread(file,1,filesize,fp2);
    file_object = json_tokener_parse(file);
    fclose(fp2);
    json_object_to_file("2.json",file_object);

    printf("-----------json infor ---------------------------\n");  
    printf("%s\n", json_object_to_json_string(infor_object));  
    printf("-----------json infor ---------------------------\n");  
 
    json_object_put(infor_object);//free 
    json_object_put(file_object);//free 
  
}  
  
  
int main(int argc, char *argv[])  
{  
    test_jsonc();  
  
    return 0;  
}  

其中：

structjson_object *file_object = NULL;

unsignedint filesize = 0;

FILE*fp;

fp= fopen("1.json", "r");

fseek(fp,0L, SEEK_END);

filesize= ftell(fp);

printf("filesizeis %d \n",filesize);

fclose(fp);

獲取了1.json的檔案大小，在下面的程式碼中讀取1.json的資料並存至2.json檔案中。

FILE*fp2;

char*file;

fp2= fopen("1.json", "r");

file= (char *)malloc(filesize + 1);

fseek(fp2,SEEK_SET, 0);

fread(file,1,filesize,fp2);

file_object= json_tokener_parse(file);

fclose(fp2);

json_object_to_file("2.json",file_object);

將檔案轉為json格式：

file_object= json_tokener_parse(file);

將json格式轉為檔案：

json_object_to_file("2.json",file_object);

PS：編譯的時候一定要依賴json庫：

gcc-o target test.c -ljson

程式執行結果：

-----------result_objectmethod ---------------------------

"GetSystemInfo"

-----------result_objectmethod---------------------------

-----------result_objectparam ---------------------------

{"DeviceId": "sn_iso_9000", "MacAddr":"AA:BB:CC:DD:EE:FF", "Visible": 1 }

-----------result_objectparam---------------------------

-----------result_object array---------------------------

[256, 257, 258 ]

-----------result_objectarray---------------------------

[0]=256

[1]=257

[2]=258

filesizeis 156

-----------jsoninfor ---------------------------

{"method": "GetSystemInfo", "param": {"DeviceId": "sn_iso_9000", "MacAddr":"AA:BB:CC:DD:EE:FF", "Visible": 1 }, "id":"101", "array": [ 256, 257, 258 ] }

-----------jsoninfor ---------------------------

同時可執行程式的目錄下會生成1.json和2.json檔案

內容相同：

#cat1.json

{"method": "GetSystemInfo", "param": {"DeviceId": "sn_iso_9000", "MacAddr":"AA:BB:CC:DD:EE:FF", "Visible": 1 }, "id":"101", "array": [ 256, 257, 258 ]}[email protected]:~/My_test/json_test$

參考文章：

[1]json-c例子http://blog.csdn.net/lanyang123456/article/details/41909369

[2]linux安裝json-chttp://www.cnblogs.com/LubinLew/p/Linux_JSON-C_Install.html