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Using in Unreal Engine - handling custom types conversion #495
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I haven't tried it, but it should be sufficient to define a
to_jsonfunction in the namespace ofFString. In the header, I did not find a namespace, so it should be sufficient to definevoid to_json(json& j, const person& p) { j = TCHAR_TO_UTF8(*value); }
(I just copied the
j = TCHAR_TO_UTF8(*value);from your example).Then you should be able to execute for an
FStringobjectf:json j = f;.What you need to do is to remove the
typename Tand it will work:template <> struct adl_serializer<FString> { ... };
@nlohmann I don't understand how that could work. How it can know to use global
to_jsonfunction for FString?@theodelrieu Tried that and now I am getting...
error C2908: explicit specialization; 'nlohmann::adl_serializer<T,void>' has already been instantiated
with
[
T=FString
]
error C2766: explicit specialization; 'nlohmann::adl_serializer<T,void>' has already been defined
with
[
T=FString
]For types that belong to you, the free function is the best approach usually, however for those which are not in your namespaces that' s not really intended.
I think that error means that you should put this piece of code at the very top of your file, because
adl_serializeris instantiated when you do this:my_type mt; // adl_serializer<my_type> gets instantiated here json j = mt;If you don't put your specialization before , you get that error message.
Ok, looks like that this actually works...
void to_json(json& j, const FString& value) { j = TCHAR_TO_UTF8(*value); }
However when I am trying to dump that JSON now, I am getting bunch of japanese characters :)
LogTemp:Warning: JSON ≻敫≹∺祍敔瑳索촀췍췍췍췍췍췍췍Ꭰ띂Ȳ
json result; FString test = TEXT("MyTest"); result["key"] = test; UE_LOG(LogTemp, Warning, TEXT("JSON %s"), result.dump().c_str());
I am not entirely sure I got that conversion to
std::stringright. Here is a source of the information: https://wiki.unrealengine.com/String_Conversions:_FString_to_FName,_FString_to_Int32,_Float_to_FStringAlso I had to use
c_str()on the dump result as the UE_LOG macro does not recognizestring_t. That last argument of UE_LOG is VarArgsSince FString is defined in the global namespaces, this is much more easier indeed.
Edit: about the conversion , I never used unreal, I don't think I can be of any help here...
@FredyC I am also not an expert. To make sure, you could change the function to
void to_json(json& j, const FString& value) { j = std::string(TCHAR_TO_UTF8(*value)); }
and then try:
json result; FString test = TEXT("MyTest"); result["key"] = test; std::cout << result << std::endl;
The first change makes the conversion to a
std::stringexplicit. The second string asks for a serialization without relying on the behavior of theUE_LOGfunction.Well first change did not help and sadly it's not possible to use
std::coutas there is no way to read output from it. The whole thing is executed from within Unreal Editor and there is no access to regular output.Anyway, I will try to figure that out on side of UE. Thanks for help!
You're welcome. I shall close this issue. But it would be great if you could share your further experience with the library and UE.
Ok, looks like that this actually works...
void to_json(json& j, const FString& value) { j = TCHAR_TO_UTF8(*value); }
However when I am trying to dump that JSON now, I am getting bunch of japanese characters :)
LogTemp:Warning: JSON ≻敫≹∺祍敔瑳索촀췍췍췍췍췍췍췍Ꭰ띂Ȳ
@FredyC, have you found any solution with this?
Ok, looks like that this actually works...
void to_json(json& j, const FString& value) { j = TCHAR_TO_UTF8(*value); }
However when I am trying to dump that JSON now, I am getting bunch of japanese characters :)
LogTemp:Warning: JSON ≻敫≹∺祍敔瑳索촀췍췍췍췍췍췍췍Ꭰ띂Ȳ
@FredyC, have you found any solution with this?
UE_LOG_UTF8 will fix that
Hi. I come from a JavaScript world where working with JSON is total breeze. We are currently working on a game using Unreal Engine 4 and we need to develop custom save system using JSON format so it can be read using Javascript somewhere else.
I kinda like approach of this library as its syntax is similar to what I am used to from JS. Sadly me as total rookie to C++ I am struggling with this a lot. I would like to make some arbitrary conversions from Unreal types to ones supported by this library.
For example here is a header file for FString type. Somewhere else I've found what I need to do for conversion to
std::stringso I've tried to add followingHowever this is failing compilation with this error. I am totally clueless what that means. Can you please help?