Json what（）：没有这样的节点

我正在尝试使用boost:：property\u树解析下面的JSON文件。

{
    "pi": 3.141,
    "temp": 3.141,
    "happy": true,
    "name": "Niels",
    "nothing": null,
    "answer": {
        "everything": 42
    },
    "list": [
        1,
        0,
        2
    ],
    "object": {
        "currency": "USD",
        "value": 42.99
    }
}

但是对于第二个节点“temp”，它给出了一个错误-

terminate called after throwing an instance of 'boost::wrapexcept<boost::property_tree::ptree_bad_path>'
  what():  No such node (temp)
Aborted (core dumped)
@ubuntu:~/git_

std::ifstream file(jsonPath, std::ifstream::binary);
  using json = nlohmann::json;
  namespace pt = boost::property_tree;
  pt::ptree root;
  pt::read_json(jsonPath, root);  // Load the json file in this ptree 
  string valPi = root.get<string>("pi");  
  string valtemp = root.get<string>("temp"); 

terminate在抛出'boost:：wrapexcept'实例后调用
what（）：没有这样的节点（temp）
中止（堆芯转储）
@ubuntu:~/git_

编写了如下代码-

terminate called after throwing an instance of 'boost::wrapexcept<boost::property_tree::ptree_bad_path>'
  what():  No such node (temp)
Aborted (core dumped)
@ubuntu:~/git_

std::ifstream file(jsonPath, std::ifstream::binary);
  using json = nlohmann::json;
  namespace pt = boost::property_tree;
  pt::ptree root;
  pt::read_json(jsonPath, root);  // Load the json file in this ptree 
  string valPi = root.get<string>("pi");  
  string valtemp = root.get<string>("temp"); 

std:：ifstream文件（jsonPath，std:：ifstream:：binary）；
使用json=nlohmann:：json；
名称空间pt=boost:：属性树；
pt:：ptree根；
pt:：read_json（jsonPath，root）；//在此ptree中加载json文件
字符串valPi=root.get（“pi”）；
字符串valtemp=root.get（“temp”）；

Boost属性树不是JSON库

如果已经包含了

nlohmann:：json

，为什么要（ab）使用它

您的选择器路径可能与JSON不匹配。很难说，因为您展示的示例正确：

#include <nlohmann/json.hpp>
#include <iostream>

int main() {
    auto root = nlohmann::json::parse(R"({
    "pi": 3.141,
    "temp": 3.141,
    "happy": true,
    "name": "Niels",
    "nothing": null,
    "answer": {
        "everything": 42
    },
    "list": [
        1,
        0,
        2
    ],
    "object": {
        "currency": "USD",
        "value": 42.99
    }
})");

    std::cout << root << "\n";
    auto valPi   = root["pi"].get<double>();
    auto valtemp = root["temp"].get<double>();

    std::cout << "Yay " << valPi << " and " << valtemp << "\n";
}

印刷品

{
    "pi": "3.141",
    "temp": "3.141",
    "happy": "true",
    "name": "Niels",
    "nothing": "null",
    "answer": {
        "everything": "42"
    },
    "list": [
        "1",
        "0",
        "2"
    ],
    "object": {
        "currency": "USD",
        "value": "42.99"
    }
}
Yay 3.141 and 3.141

{"pi":3.141E0,"temp":3.141E0,"happy":true,"name":"Niels","nothing":null,"answer":{"everything":42},"list":
[1,0,2],"object":{"currency":"USD","value":4.299E1}}
Yay 3.141 and 3.141

{"answer":{"everything":42},"happy":true,"list":[1,0,2],"name":"Niels","nothing":null,"object":{"currency"
:"USD","value":42.99},"pi":3.141,"temp":3.141}
Yay 3.141 and 3.141

没问题

但是，请注意，所有类型信息是如何丢失的，这只是触及PropertyTree中“限制”的表面：

使用boostjson 严肃点：

#include <boost/json.hpp>
#include <iostream>

int main() {
    auto root = boost::json::parse(R"({
    "pi": 3.141,
    "temp": 3.141,
    "happy": true,
    "name": "Niels",
    "nothing": null,
    "answer": {
        "everything": 42
    },
    "list": [
        1,
        0,
        2
    ],
    "object": {
        "currency": "USD",
        "value": 42.99
    }
})");

    std::cout << root << "\n";
    auto valPi   = root.at("pi").get_double();
    auto valtemp = root.at("temp").get_double();

    std::cout << "Yay " << valPi << " and " << valtemp << "\n";
}

使用

#include <nlohmann/json.hpp>
#include <iostream>

int main() {
    auto root = nlohmann::json::parse(R"({
    "pi": 3.141,
    "temp": 3.141,
    "happy": true,
    "name": "Niels",
    "nothing": null,
    "answer": {
        "everything": 42
    },
    "list": [
        1,
        0,
        2
    ],
    "object": {
        "currency": "USD",
        "value": 42.99
    }
})");

    std::cout << root << "\n";
    auto valPi   = root["pi"].get<double>();
    auto valtemp = root["temp"].get<double>();

    std::cout << "Yay " << valPi << " and " << valtemp << "\n";
}

---

您不应该使用

root.get

？