json-c

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了解json-c library

更新記錄

item note
20160909 第一版

目錄

JSON

JSON (JavaScript Object Notation)

Introducing JSON

[json]
  • object
    An object is an unordered set of name/value pairs. An object begins with { (left brace) and ends with } (right brace).
    Each name is followed by : (colon) and the name/value pairs are separated by , (comma).
    由大括號 { }包起來
    由逗號(,)分開每一組
    每一組使用(key-value)方式儲存 (即 name-value)
[object]

  • array
    An array is an ordered collection of values.
    An array begins with [ (left bracket) and ends with ] (right bracket). Values are separated by , (comma).
    由中括號 { }包起來

    [array]

  • value
    A value can be a string in double quotes, or a number, or true or false or null, or an object or an array
    These structures can be nested.

[value]

json object的鍵值(key)，一定要用文字做鍵值

json-c example

json-c

  • json_object.h
    json_object_object_add - Add an object field to a json_object of type json_type_object
    json_object_new_int - Create a new empty json_object of type json_type_int
    json_object_get_string_len - Get the string length of a json_object

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     * @param obj the json_object instance
     * @param key the object field name (a private copy will be duplicated)
     * @param val a json_object or NULL member to associate with the given field
    extern void json_object_object_add(struct json_object* obj, const char *key,
    				   struct json_object *val);

    struct json_object* json_object_new_int(int32_t i);
    struct json_object* json_object_new_int64(int64_t i);
    struct json_object* json_object_new_double(double d);
    struct json_object* json_object_new_string(const char *s);
    struct json_object* json_object_new_string_len(const char *s, int len);

    int32_t json_object_get_int(struct json_object *obj);
    int64_t json_object_get_int64(struct json_object *obj);
    double json_object_get_double(struct json_object *obj);
    const char* json_object_get_string(struct json_object *obj);
    int json_object_get_string_len(struct json_object *obj);

  • type

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    typedef enum json_type {
      /* If you change this, be sure to update json_type_to_name() too */
      json_type_null,
      json_type_boolean,
      json_type_double,
      json_type_int,
      json_type_object,
      json_type_array,
      json_type_string,
    } json_type;

json_object_put

  • json_object_put
    主要清除之前產生的記億体，防止memory leak
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    int json_object_put(struct json_object *jso)
    {
      if(jso)
      {
        jso->_ref_count--;
        if(!jso->_ref_count)
        {
          if (jso->_user_delete)
            jso->_user_delete(jso, jso->_userdata);
          jso->_delete(jso);
          return 1;
        }
      }
      return 0;
    }

example

  • main.c

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    $ cat main.c
    #include <stdlib.h>
    #include <stdio.h>
    #include <unistd.h>
    #include <string.h>

    #include "json.h"


    void getValByKey(json_object* jobj, const char *sname)
    {
        json_object *pval =NULL;
        enum json_type type;
        pval = json_object_object_get(jobj, sname);

        if(NULL != pval){
            type = json_object_get_type(pval);
            switch(type)
            {
                case json_type_string:
                    printf("key:%s, value:%s\n",sname,json_object_get_string(pval));
                    break;
                case json_type_int:
                    printf("key:%s, value:%d\n",sname,json_object_get_int(pval));
                    break;
                default:
                    printf("default: key:%s\n",sname);
                    break;
            }
        }
    }

    int main(void)
    {
        json_object *pobj = NULL;
        pobj = json_object_from_file("/root/t1.json");
        getValByKey(pobj,"green");
        json_object_object_del(pobj,"red");
        json_object_object_add(pobj,"black",json_object_new_string("#000"));
        json_object_object_add(pobj,"iblack",json_object_new_int(0));
        getValByKey(pobj,"iblack");

        json_object_to_file("/tmp/t1-new.json",pobj);
        json_object_put(pobj);
        return 0;
    }

  • test

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    gk350a :[~]# ./json-t1 
    key:green, value:#0f0
    key:iblack, value:0
    gk350a :[~]# cat /tmp/t1-new.json 
    gk350a :[~]# cat /tmp/t1-new.json 
    {"green":"#0f0","blue":"#00f","black":"#000","iblack":0}gk350a :[~]# 
    gk350a :[~]# cat t1.json 
    {
        "red":"#f00",
        "green":"#0f0",
        "blue":"#00f",
    }
    gk350a :[~]#

參考