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I am trying to parse the JSON structure using nlohmann's json.hpp . But I am not to create the JSON structure from the string. I have tried all the way, but still it is failing.

My requirement is to:

1) Create the JSON structure from the string.

2) Find the value of "statusCode" from it.

After trying for so long time, I am really getting doubt, does nlohmann's json parser support nested JSON or not.

#include "json.hpp"
using namespace std;

int main(){

    // giving error 1
    nlohmann::json strjson = nlohmann::json::parse({"statusResp":{"statusCode":"S001","message":"Registration Success","snStatus":"Active","warrantyStart":"00000000","warrantyEnd":"00000000","companyBPID":"0002210887","siteBPID":"0002210888","contractStart":"00000000","contractEnd":"00000000"}});

    // Giving error 2:
   auto j= "{
    "statusResp": {
        "statusCode": "S001",
        "message": "Registration Success",
        "snStatus": "Active",
        "warrantyStart": "20170601",
        "warrantyEnd": "20270601",
        "companyBPID": "0002210887",
        "siteBPID": "0002210888",
        "contractStart": "00000000",
        "contractEnd": "00000000"
    }
   }"_json;

   // I actually want to get the value of "statusCode" code from the JSOn structure. But no idea how to parse the nested value.
    return 1;

}

Below are the error for both the initialisations:

//ERROR 1:
test.cpp: In function 'int main()':
test.cpp:17:65: error: expected '}' before ':' token
     nlohmann::json strjson = nlohmann::json::parse({"statusResp":{"statusCode":"S001","message":"Registration Success","snStatus":"Active","warrantyStart":"00000000","warrantyEnd":"00000000","companyBPID":"0002210887","siteBPID":"0002210888","contractStart":"00000000","contractEnd":"00000000"}});

// ERROR 2:
hemanty@sLinux:/u/hemanty/workspaces/avac/cb-product/mgmt/framework/src/lib/libcurl_cpp$g++ test.cpp -std=gnu++11
test.cpp: In function 'int main()':
test.cpp:27:17: error: expected '}' before ':' token
     "statusResp": {
4

2 回答 2

4

由于"是开始和结束字符串文字的字符，因此您不能在字符串中"包含字符而不在其前面放置一个字符\。

std::string str = " "statusCode":"5001" "; //This does not work

std::string str = " \"statusCode\":\"5001\" "; //This will work

当您想要制作包含大量字符串的字符串时，一个更简单的选择"是使用R"" 字符串文字。然后你可以这样写。

std::string str = R"("statusCode":"5001")";

如果我们现在将其转换为您的 json 示例，则解析字符串的正确方法将是以下之一。

auto j3 = json::parse("{ \"happy\": true, \"pi\": 3.141 }");
// and below the equivalent with raw string literal
auto j3 = json::parse(R"({"happy": true, "pi": 3.141 })");

//Here we use the `_json` suffix 
auto j2 = "
{
    \"happy\": true,
    \"pi\": 3.141
}"_json;
// Here we combine the R"" with _json suffix to do the same thing.
auto j2 = R"(
{
    "happy": true,
    "pi": 3.141
  }
)"_json;

自述文件中的示例

于 2018-02-19T11:36:20.647 回答
1

如果这是您需要的：

std::string ss= R"(
{
    "test-data":
    [
        {
            "name": "tom",
            "age": 11
        },
        {
            "name": "jane",
            "age": 12
        }
    ]
}
)";

json myjson = json::parse(ss);
auto &students = myjson["test-data"];

for(auto &student : students) {
    cout << "name=" << student["name"].get<std::string>() << endl;
}

或者：

json myjson = { {"name", "tom"}, {"age", 11} };
cout << "name=" << myjson["name"].get<std::string>() << endl;
于 2021-01-29T04:32:06.910 回答