JSON+＜boost/property_tree/json_parser.hpp＞+＜boost/property_tree/ptree.hpp＞

最新推荐文章于 2024-08-22 16:06:07 发布

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最新推荐文章于 2024-08-22 16:06:07 发布

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文章标签： json

本文链接：https://blog.youkuaiyun.com/qq_42370809/article/details/126274557

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一、JSON定义

JavaScript Object Notation
由字符串化的键值对构成，总的来说就是一个字符串表示的对象。

1. 是一种数据交换格式

虽然一开始用于JavaScript，但是主要是用于web中的数据交换，就是一种数据交换格式，而且很好懂，很易读，也有利于数据传输。

2.支持的数据类型（值的数据类型）

对象：{}括起来的键值对，用逗号,分隔，键值格式是键:值，json本身就是一个对象。
数值：十进制，支持科学计数法
字符串：""括起来的0~n个字符，支持转义字符
布尔：true、false
数组：[]括起来的多个值，以,分割
空：null

3. 例子：

{
    "version": "test_json v1.0",
    "description": "this demo used to practice json analysis",
    "test_number": "78322",
    "path_set": {
        "load_path": ".\/data",
        "save_path": ".\/result"
    },
    "camera_device": {
        "name": "cam1",
        "path": "\/sys\/dev\/",
        "FOV": [
            "30",
            "50"
        ],
        "RES": [
            "640",
            "480"
        ],
        "Intrinsic": {
            "fx": "50.2155",
            "fy": "45.1245",
            "cx": "0.55454",
            "cy": "0.55488"
        }
    },
    "T_Matrix": {
        "t1": [
            "1",
            "2",
            "3"
        ],
        "t2": [
            "4",
            "5",
            "6"
        ]
    },
    "other_info": {
        "info_1": {
            "info": "hello world",
            "Matrix": [
                "21",
                "21",
                "21",
                "21"
            ]
        },
        "info_2": {
            "info": "hello C++",
            "Matrix": [
                "22",
                "22",
                "22",
                "22"
            ]
        }
    },
    "location1": [
        "23",
        "23",
        "2333"
    ],
    "location2": [
        "233",
        "233",
        "23333"
    ],
    "test_choice": [
        {
            "name": "test1",
            "enable": "true"
        },
        {
            "name": "test2",
            "enable": "false"
        },
        {
            "name": "test1",
            "enable": "true"
        }
    ],
    "end_desc": "thank you"
}

二、使用boost：构造、读取、写入、增删查改

<boost/property_tree/ptree.hpp>负责构造
<boost/property_tree/json_parser.hpp>负责以json格式输出

1. 构造数组

#include <boost/property_tree/ptree.hpp>
namespace pt = boost::property_tree;
pt::tree root;
pt::ptree child1, child2,child3, child4;
pt::ptree childs;
//单独一个数值
child1.put("", 2);
//单独一个字符串
child2.put("", "asdh");
//对象
child3.put("key0", "val0");
//构造数组，主意childs必须只有key为""的，不能有其他。不然会退化为对象
//把数值加入数组
childs.push_back(make_pair("", child1));
childs.push_back(make_pair("", child2));
childs.push_back(make_pair("", child3));
childs.push_back(make_pair("", childs));
//键为list，值为childs数组
root.put("list", childs);
/*
{
	"list":
		[
			2, 
			"asdh", 
			{"key0", "val0"}, 
			[2, "asdh", {"key0", "val0"}]
		]
}
*/

2. 从文件/流读入，写入到流/文件

使用头文件#include <boost/property_tree/json_parser.hpp>实现读取和写入json

从文件读入(给文件名）

#include <boost/property_tree/json_parser.hpp>
namespace pt = boost::property_tree;
string file_name = "./test.json";
pt::ptree json_root;
pt::read_json(file_name , json_root);

从流读入，文件流ifstream和string流stringstream都行

string file_name = "./test.json";
ifstream fs;
fs.open(file_name);
pt::read_json(fs, json_root);

写入文件(给文件名)

pt::write_json(filename, json_root);

写入流，文件流或string流,true代表美化，false代表不美化，美化就是换行，如果ss是stringstream，注意传输的时候用ss.str()，cout << ss.str() << endl;

pt::write_json(ss, json_root, true);

false=

{"version":"test_json v1.0","description":"this demo used to practice json analysis","test_number":"78322","path_set":{"load_path":".\/data","save_path":".\/result"},"camera_device":{"name":"cam1","path":"\/sys\/dev\/","FOV":["30","50"],"RES":["640","480"],"Intrinsic":{"fx":"50.2155","fy":"45.1245","cx":"0.55454","cy":"0.55488"}},"T_Matrix":{"t1":["1","2","3"],"t2":["4","5","6"]},"other_info":{"info_1":{"info":"hello world","Matrix":["21","21","21","21"]},"info_2":{"info":"hello C++","Matrix":["22","22","22","22"]}},"location1":["23","23","2333"],"location2":["233","233","23333"],"test_choice":[{"name":"test1","enable":"true"},{"name":"test2","enable":"false"},{"name":"test1","enable":"true"}],"end_desc":"thank you","a":{"info_1":{"info":"hello world","Matrix":["21","21","21","21"]},"info_2":{"info":"hello C++","Matrix":["22","22","22","22"]}},"b":{"load_path":".\/data","save_path":".\/result"}}

true=

{
    "version":"test_json v1.0",
    "description":"this demo used to practice json analysis",
    "test_number":78322,
    "path_set":{
        "load_path":"./data",
        "save_path":"./result"
    },
    "camera_device":{
        "name":"cam1",
        "path":"/sys/dev/",
        "FOV":[30,50],
        "RES":[640,480],
        "Intrinsic":{
            "fx":50.2155,
            "fy":45.1245,
            "cx":0.55454,
            "cy":0.55488
        }
    },
    "T_Matrix":{
        "t1":[1,2,3],
        "t2":[4,5,6]
    },
    "other_info":{
        "info_1":{
            "info":"hello world",
            "Matrix":[21,21,21,21]
        },
        "info_2":{
            "info":"hello C++",
            "Matrix":[22,22,22,22]
        }
    },
    "location1":[23,23,2333],
    "location2":[233,233,23333],
    "test_choice":[
        {
            "name":"test1",
            "enable":true
        },
        {
            "name":"test2",
            "enable":false
        },
        {
            "name":"test1",
            "enable":true
        }
    ],
    "end_desc":"thank you"
}

3. 添加

add：add(key, value)，add_child可以用来添加数组和对象
add 不会覆盖原来的key:value，也就是

root.add("list", "1234");
root.add("list", "1234");
/*
{
	"list":"1234",
	"list":"1234"
}
*/

put和put_child和add类似，不同的是put对于相同的key:value并不会重复添加，也就是

root.put("list", "1234");
root.put("list", "1234");
/*
{
	"list":"1234",
}
*/

push_back/push_front：提供一个pair，必须是键:对象/数组

root.push_back(make_pair("123", child1));

如果单纯想插入一个非对象和数组的值，可以这样

childs2.put("", "sda");
root.push_back(make_pair("123", childs2));

4. 查找

查找值（非数组和对象）

string value0 = root.get<string>("key0");
double value1 = root.get<double >("key1");
int value2 = root.get<int>("key2");
bool value3 = root.get<bool>("key3");

查找对象/数组

pt::ptree value4  = root.get_child("key4");

遍历：
- 范围for
  对于数组，可以用下边这种来获取每一个数组的值

for (pt::ptree::value_type &value : value4)
{
    //2.获得每一个子节点的值，并将其放进vector
	T tValue =value.second.get_value<T>();
	vecData.push_back(tValue);
}

- 迭代器，其中getArrayDataFromJson是把数组存到vector

pt::ptree::iterator it;
    for(it = ele_other.begin();it!=ele_other.end();it++)
    {
        cout << it->first << endl;;
        //对每个子节点对象（即sub_value.second）进行解析
        string sub_info_temp = it->second.get<string>("info");
        vector<int> sub_v_temp;
        bool sub_v_temp_flag = getArrayDataFromJson(sub_v_temp,it->second,"Matrix");
        cout<<sub_info_temp<<"=[";
        for(auto v:sub_v_temp)cout<<v<<" ";
        cout<<"]"<<endl;
    }

//解析普通数组
template <class T>
bool getArrayDataFromJson(std::vector<T> &vecData, pt::ptree & nodeJSON, string path) {
    //1.循环遍历数组中所有的子节点（数组中的每一个元素）
	for (pt::ptree::value_type &value : nodeJSON.get_child(path))
	{
        //2.获得每一个子节点的值，并将其放进vector
		T tValue =value.second.get_value<T>();
		vecData.push_back(tValue);
	}
	return true;
}

5.删除

使用erase(key)删除键key的所有值

root.erase("list");

6.修改

通过迭代器修改：

root.begin()->second.put_value("wasdasd");

通过键修改：注意只适合对象中的键唯一，不然只会找到第一个key对应的，如果有多个建议用迭代器修改

root.get_child("list").put_value("asd");