Help request

[abdessattar]

Hello,
I want to thank you for the important advice. I get what I want but with simple class.
When I tried your solution with singleton and other specific classes. I got this error "C2338 could not find to _json() method in T's namespace ".
Really, I need your help for advancing as soon as possible.
thank you in advance,
Best regards,

[nlohmann]

Can you provide the code you try to compile?

[abdessattar]

Ok, but the problem that I work on specifec private project.
You find below the main code.

#include <iostream>
#include <stdio.h>
#include <fstream>
#include "StdAfx.h"
#include <stdlib.h>
#include "C:\Users\abahri\Desktop\visual studio\Project\first part\gui\g4\v5.1.0.0\v5.1.0.0\GUI_Descr.xsd.Output\SourceCodeCPP\GUI_DescrLib.h"
#include "C:\Users\abahri\Desktop\visual studio\Project\first part\gui\g4\v5.1.0.0\v5.1.0.0\GUI_Descr.xsd.Output\SourceCodeCPP\GUI_DescrLib\DataStream.h"
#include "C:\Users\abahri\Desktop\visual studio\Project\first part\gui\g4\v5.1.0.0\v5.1.0.0\GUI_Descr.xsd.Output\SourceCodeCPP\GUI_DescrLib\BaseDir.h"
#include "C:\Users\abahri\Desktop\visual studio\Project\first part\gui\g4\json-develop\json-develop\src\json.hpp"
using namespace LtXmlLib5;
using namespace GUI_DescrLib;
using json = nlohmann::json;

bool SimpleTestGUI_DescrLibCDataStream(LPCTSTR);
int main()
{

	if(SimpleTestGUI_DescrLibCDataStream(_T("<UNCOMMENT & INSERT A SAMPLE XML FILENAME HERE>")));
	std::cout << "hello";
	system("pause");
	return 0;
}


bool SimpleTestGUI_DescrLibCDataStream(LPCTSTR lpctFilename)
{
	GUI_DescrLib_Classes ecls;
	
	LtXmlLib5Data::CParentElementInfo elm = GUI_DescrLib::CClassFactory::getinfoclass(ecls, lpctFilename);
		json j;
		j["ms_pParentElementInfo"] = elm;

			return false;
		
}

[nlohmann]

In line j["ms_pParentElementInfo"] = elm;, you try to assign type LtXmlLib5Data::CParentElementInfo to nlohmann::json. Such a conversion is not provided directly by the library (only default types such as strings, numbers, etc. are supported out of the box). Therefore, the library tries to find whether you provided a to_json() function in the namespace of your type (LtXmlLib5Data in your case).

You need to define a method void to_json(json& j, const CParentElementInfo& e) in namespace LtXmlLib5Data where you implement the conversion from a LtXmlLib5Data::CParentElementInfo object e to a nlohmann::json object j. This is documented in https://github.com/nlohmann/json#arbitrary-types-conversions.

[theodelrieu]

We could add support for enum classes too, this is quite trivial, and won't conflict with existing to_json(json, my_enum) methods

[nlohmann]

That would be great. Is this related to #513?

[theodelrieu]

Yes it is!

[abdessattar]

Is it necessary that the method have two arguments, we cannot define it only with first argument (json)?
Thank you in advance,

[nlohmann]

No, it has to have two arguments.

[abdessattar]

Because I get the same error, despite I define it with two arguments.
To your mind what is the solution?

[nlohmann]

Did you try what I proposed in #539 (comment)?

[abdessattar]

yes I tried, you will find my test in this code.
Such as my class is a singleton.

#include "StdAfx.h"
#include <iostream>
#include <stdio.h>
#include "GUI_DescrLib.h"
#include "BaseDir.h"

#include "D:\Sources\serialization_avec_json&GUIdescr2015\json-develop\json-develop\src\json.hpp"
using nlohmann::json;

using namespace LtXmlLib5;
using namespace std;
using namespace GUI_DescrLib;



// forward declarations

void to_json(json& j, const CClassFactory & p, GUI_DescrLib_Classes eCls, LPCTSTR strElementName);

/// <summary>
/// The main entry point for the application.
/// </summary>
int main(int argc, char* argv[])
{

	
	 
	system("pause");
	return 0;
}


void to_json(json& j) {

	GUI_DescrLib_Classes eCls = ClsName_CBaseDir;
	CBaseDirPtr	elm = CBaseDir::CreateInstance();

	j = json{ { "name", CBaseDir::GetparentElement() },{ "address", CBaseDir::Getelementinfo() },{ "age", CBaseDir:: Getattributrinfo() } };
}

[nlohmann]

You need to define the to_json function in the namespace of the class you want to convert to JSON. It has to have exactly two parameters: json & and a const reference of your class type.

[abdessattar]

The problem that the class type is a singleton, so Ihave to create one and only one instance of this class.

[nlohmann]

I don't understand. The to_json function is static.

[abdessattar]

As I said in the previous comment, the classes in my project are singletons and their attributes are static. So can I define thes method in the classes as a static method?
Really I need your help.
Thank you in advance,

[nlohmann]

I see. Then you cannot use this mechanism. You can define any function that returns a json.

[nlohmann]

btw: this is a strange implementation of a singleton as you have no instance at all. If you follow approaches like http://stackoverflow.com/questions/1008019/c-singleton-design-pattern you would have exactly one instance and could the approach described in the README.

[abdessattar]

Good morning,
In which section the approach described?
Thank you in advance,

[nlohmann]

See #539 (comment)

[abdessattar]

To my mind, Ihave to add my one "adl_serializer", would do you please show an example of it.
Because I copied the example i this link.

template <typename CBaseDir>
struct adl_serializer {
	static void to_json(json& j, const	CBaseDir& value) {
	 tojson(json& j);
	}

};

But I get this error "syntax error;identifier'json'".
Thank you in advance

[nlohmann]

Did you add using nlohmann::json; to your code.

[theodelrieu]

There is an example with boost::optional in the readme, it seems like your use case