{
    "datastreams": [
        {
            "id": "tempture","datapoints": [
                {
                    "at": "2017-02-04T20:33:45","value": 19
                }
            ]
        }
    ]
}

如何用cJSON解析上述的json格式的字符串;

首先分析下:

根节点下有一个键是datastreams,值是一个数组;

数组里面有2条记录,第一条是一个键值对,第二条当然也是键值对,

但是这个键值对的值是嵌套的,即值也是由两个键值对组成的;

//1. 首先创建一个根节点,即一个空的大括号  {}
	root=cJSON_CreateObject();
	
	//2.添加一个键值对,键是datastrems,值是个数组,用cJSON_CreateArray来创建
	cJSON_AddItemToObject(root,"datastreams",subdir=cJSON_CreateArray());
	
	//3.这个数组里面又是一个对象,所以用cJSON_CreateObject来创建
	cJSON_AddItemToObject(subdir,"dira",dir1=cJSON_CreateObject());
	
	//4.往新创建的对象里添加键值对 "id","tempture"
	cJSON_AddStringToObject(dir1,"id","tempture");
	
	//5.再添加一个键值对,键是datapoints  对是一个数组,用cJSON_CreateArray来创建
	cJSON_AddItemToObject(dir1,"datapoints",subdir2=cJSON_CreateArray()); //再次嵌套一个数组
	
	//6.数组里是一个对象用cJSON_CreateObject来创建,里面有两个键值对
	cJSON_AddItemToObject(subdir2,"dirb",dir2=cJSON_CreateObject());
	
	//7.添加两个键值对 
	cJSON_AddStringToObject(dir2,"at","2017-02-04T20:33:45");
	cJSON_AddNumberToObject(dir2,"value",19);
	
	out=cJSON_Print(root);	cJSON_Delete(root);	printf("%s\n",out);	myfree(out);

再来看一个例子:

[
 
{name:"中国",province:[ { name:"黑龙江",cities:{ city:["哈尔滨","大庆"] }}]},{name:"广东",cities:{ city:["广州","深圳","珠海"] } }
 
]

cJSON *root,*dir1,*dir2,*dir3,*dir4,*dir5;
		
		root=cJSON_CreateArray();
 
		cJSON_AddItemToObject(root,"root1",dir1=cJSON_CreateObject());//发现里面第一个就是{}套着,那就将该{}里的内容都填写好
		//分析下,这里第一个元素是字符串键值对
		cJSON_AddStringToObject(dir1,"name","中国");
		//第二个元素键是province,值是个数组
		cJSON_AddItemToObject(dir1,"province",dir2=cJSON_CreateArray());
		//数组里又是一个对象,里面有两个键值对
		cJSON_AddItemToObject(dir2,"dir3",dir3=cJSON_CreateObject());
		cJSON_AddStringToObject(dir3,"黑龙江");
		cJSON_AddItemToObject(dir3,"cities",dir4=cJSON_CreateObject());
		//对象里是一个键值对
		//键是city,值是一个数组
		cJSON_AddItemToObject(dir4,"city",dir5=cJSON_CreateArray());
		cJSON_AddStringToObject(dir5,"xxx","哈尔滨");
		cJSON_AddStringToObject(dir5,"大庆");
		
		//-------------------------------------------------------		
		cJSON_AddItemToObject(root,"root2",dir1=cJSON_CreateObject());
		cJSON_AddStringToObject(dir1,"广东");
		cJSON_AddItemToObject(dir1,dir2=cJSON_CreateObject());
		cJSON_AddItemToObject(dir2,dir3=cJSON_CreateArray());
		cJSON_AddStringToObject(dir3,"广州");
		cJSON_AddStringToObject(dir3,"深圳");
		cJSON_AddStringToObject(dir3,"珠海");
		
		out=cJSON_Print(root);	cJSON_Delete(root);	
		buf_length=sprintf(buf,"%s",out);
		
		printf("%s\n",out);	myfree(out);