c++ - 在 rapidjson 中使用 AddMember 获取空值

Question

我正在尝试使用 RapidJson 和 VC++ 创建 json 字符串。下面是我的代码:

WDocument saveDoc; 
WValue settingDoc(kObjectType);
settingDoc.AddMember("BOOK_ID",  "456723", saveDoc.GetAllocator());
settingDoc.AddMember("BOOK_FOUND",  true, saveDoc.GetAllocator());
WValue wImplVal;
wImplVal.SetString(BookName, saveDoc.GetAllocator()); //TCHAR BookName[MAX_PATH]
settingDoc.AddMember("BOOK_NAME",  wImplVal, saveDoc.GetAllocator());     //gets correct book name
settingDoc.AddMember("BOOK_NICK_NAME",wImplVal,saveDoc.GetAllocator());//gets null value in wImplVal 
saveDoc.SetObject();    
saveDoc.AddMember("BOOK_INFO", settingDoc, saveDoc.GetAllocator());

我第二次得到 NULL 值，在使用 wImplVal 时，即使我没有修改它。rapidjson中两个键加一个值有什么特殊规则吗？提前致谢。

Answer 1

如果你仔细阅读 this，尤其是“移动语义”部分，你会发现 rapidjson 值使用移动语义，所以当你将它传递给 AddMember 时，它会移出现有值并将其替换为 Null。

As RapidJSON supports C++03, it adopts move semantics using assignment operator, and all other modifying function like AddMember(), PushBack().

所以你必须重新设置值才能得到你想要的。

WDocument saveDoc; 
WValue settingDoc(kObjectType);
settingDoc.AddMember("BOOK_ID",  "456723", saveDoc.GetAllocator());
settingDoc.AddMember("BOOK_FOUND",  true, saveDoc.GetAllocator());
WValue wImplVal;
wImplVal.SetString(BookName, saveDoc.GetAllocator()); //TCHAR BookName[MAX_PATH]
settingDoc.AddMember("BOOK_NAME",  wImplVal, saveDoc.GetAllocator());     //gets correct book name
wImplVal.SetString(BookName, saveDoc.GetAllocator());
settingDoc.AddMember("BOOK_NICK_NAME",wImplVal,saveDoc.GetAllocator());//gets null value in wImplVal 
saveDoc.SetObject();    
saveDoc.AddMember("BOOK_INFO", settingDoc, saveDoc.GetAllocator());