c++json nlohmann 和 poco json 使用

C++使用nlohmann json

最好用的c++ json库是 nlohmann

https://blog.csdn.net/wphkadn/article/details/97417700

把变量写成json容易，可是把json变成变量就要复杂一点，不过对于nlohmann一点都不复杂

 

参考

http://www.it1352.com/497248.html

#include "Poco/JSON/Parser.h"
#include "Poco/JSON/ParseHandler.h"
#include "Poco/JSON/Stringifier.h"

using Poco::JSON::ParseHandler;
using Poco::JSON::Stringifier;
using Poco::JSON::Object;
using Poco::JSON::Parser;
using Poco::Dynamic::Var;
using Poco::DynamicStruct;

void objPrint(Object& obj, const std::string& name = "")
{
    for (Object::ConstIterator it = obj.begin(),
        end = obj.end(); it != end; ++it)
    {
        if (!name.empty()) std::cout << name << ':';
        std::cout << it->first << ':';
        if (it->second.type() == typeid(Object::Ptr))
        {
            Object::Ptr p = it->second.extract();
            objPrint(*p, it->first);
        }
        else
             std::cout << it->second.toString() << std::endl;
    }
}

int main(int, char**)
{
    typedef std::map PersonMap;

    std::string timeStamp = "2015-05-14T17:47:21.999Z";
    Poco::Int32 identifier = 3;
    std::string name = "john smith";
    PersonMap metaData;
    metaData.insert(PersonMap::value_type("william", 45));

    Object obj(true);
    obj.set("ts", timeStamp);
    obj.set("name", name);
    obj.set("identifier", identifier);
    Object::Ptr pMD = new Poco::JSON::Object(true);
    for (PersonMap::iterator it = metaData.begin(),
        end = metaData.end(); it != end; ++it)
    {
        pMD->set("middle_name", it->first);
        pMD->set("age", it->second);
    }
    obj.set("metadata", pMD);

    std::ostringstream os;
    obj.stringify(os, 2);
    std::cout << os.str() << std::endl;

    Parser parser;
    Var result = parser.parse(os.str());

    Object::Ptr pObj = result.extract();
    objPrint(*pObj);

    return 0;
}

 

https://blog.csdn.net/yuhaiyang457288/article/details/47190117?utm_source=blogxgwz2

 

#include
#include 
#include 
#include "Poco/JSON/Parser.h"
#include "Poco/JSON/ParseHandler.h"
#include "Poco/JSON/JSONException.h"
#include "Poco/StreamCopier.h"
#include "Poco/Dynamic/Var.h"
#include "Poco/JSON/Query.h"
#include "Poco/JSON/PrintHandler.h"


using namespace Poco::Dynamic;
using namespace Poco;
using std::string;

// json 的简单示例。
void JsonGet( )
{
    string jsonString = "{ \"name\" : \"yuhaiyang\" }";
    JSON::Parser parser;
    Dynamic::Var result;
    parser.reset();

    result = parser.parse( jsonString );
    JSON::Object::Ptr pObj = result.extract();
    Dynamic::Var ret = pObj->get( "name2" );
    if ( ret.isEmpty() )
    {
        std::cout << "is null" << std::endl;
    }else
    {
        std::cout << ret.toString() << std::endl;
    }
}

//在　json 里加入数组。
void JsonArry( void )
{
    JSON::Object jsnObj;
    JSON::Array jsnArry;
    JSON::Object subObj1;
    JSON::Object subObj2;

    jsnObj.set( "command", "createuser" );

    subObj1.set( "name", "yuhaiyang");
    subObj1.set( "pass", "123" );

    subObj2.set( "name", "cj" );
    subObj2.set( "pass", "456" );

    jsnArry.add( subObj1 );
    jsnArry.add( subObj2 );

    jsnObj.set( "userinfo", jsnArry );

    std::stringstream  jsnString;
    jsnObj.stringify( jsnString, 3 );
    std::cout << jsnString.str() << std::endl;

}


//解析数据
void JsonGetArry( void )
{
/*-------------------构造包含Array的JSON（string类型）--------------------------------*/
    JSON::Object jsnObj;
    JSON::Array jsnArry;
    JSON::Object subObj1;
    JSON::Object subObj2;

    jsnObj.set( "command", "createuser" );

    subObj1.set( "name", "yuhaiyang");
    subObj1.set( "pass", "123" );

    subObj2.set( "name", "cj" );
    subObj2.set( "pass", "456" );

    jsnArry.add( subObj1 );
    jsnArry.add( subObj2 );

    jsnObj.set( "userinfo", jsnArry );

    std::stringstream  jsnOstream;
    jsnObj.stringify( jsnOstream, 3 );

    string jsnStr = jsnOstream.str();

    std::cout << "原数据:\n" << jsnStr << "\n\n\n" << std::endl;


    //--------------------------解析数组-----------------------------
    JSON::Parser parse;
    Dynamic::Var json = parse.parse( jsnStr );
    JSON::Object::Ptr pObj = json.extract();
    JSON::Array::Ptr pArry = pObj->getArray( "userinfo" );

    JSON::Array::ConstIterator it = pArry->begin();
    //把数组里的所有内容打印出来
    //当然也可以把每个对象拿出来用。
    for ( ; it != pArry->end(); it++ )
    {
        std::cout << it->toString() << std::endl;
    }

}

int main()
{
    JsonGet();
    JsonArry();
    JsonGetArry();
}