LNK2019: “Unresolved external symbol” with rapidjson

问题

I have a Visual C++ Project in which I added the rapidjson library, which is tested to be working properly. But when I add a rapidjson::Document type to the nested class is throwing a LNK2019 error when I try to compile. The project is a dynamic library to create a DLL.

This are the definitions in my main.h:

class coreBD {
string conn;
string proxy;
int type;
Document test;

enum dataBases {
    Sqlite,
    SqlServer,
    None
};

string queryBD(string sSQL);
string queryHTTP(string sSQL);

string httpRequest(string url, string proxy);

static string getNow(string format);
static string urlEncode(string url);
static bool startsWith(string source, string with);

public:

enum access {
    dbConn,
    HTTPProtocol
};

//Nested class
class jsonObj {
    string jsonStr;
    string message;
    Document doc; //HERE IS THE PROBLEM
    bool validMsg;

public:
    enum response {
        FullResponse,
        SQLResponse
    };

    jsonObj(string json);
    string getJsonStr(response rType);
    string getErrorMsg();
    bool isValidResponse();
};

coreBD(string connStr, access connType);
jsonObj query(string sSQL);
void setProxy(string proxy);
};

This is the error:

error LNK1120: 1 unresolved externals

error LNK2019: unresolved external symbol "private: __thiscall rapidjson::GenericValue,class rapidjson::MemoryPoolAllocator >::GenericValue,class rapidjson::MemoryPoolAllocator >(class rapidjson::GenericValue,class rapidjson::MemoryPoolAllocator > const &)" (??0?$GenericValue@U?$UTF8@D@rapidjson@@V?$MemoryPoolAllocator@VCrtAllocator@rapidjson@@@2@@rapidjson@@AAE@ABV01@@Z) referenced in function "public: __thiscall rapidjson::GenericDocument,class rapidjson::MemoryPoolAllocator >::GenericDocument,class rapidjson::MemoryPoolAllocator >(class rapidjson::GenericDocument,class rapidjson::MemoryPoolAllocator > const &)" (??0?$GenericDocument@U?$UTF8@D@rapidjson@@V?$MemoryPoolAllocator@VCrtAllocator@rapidjson@@@2@@rapidjson@@QAE@ABV01@@Z)

The error disappears when I comment the line commented with HERE IS THE PROBLEM in the code. As you can see, the use of the test variable in the coreBD class causes no error. The mere existence of the variable of type rapidjson::Document in the nested class causes de error to show; it doesn't matter if I use it or not.

What could be the problem?

EDIT:

New information gathered.

The problem appears when I use the nested class inside the parent one, but only in the return of a method. In other words: I can create everything with rapidjson::Document type as a member variable, I can create a method in coreBD class with type jsonObj, I can instantiate jsonObj inside that methods, but I cannot return a value of type jsonObj if the class jsonObj has a rapidjson::Document member variable declared.

For example this new created method:

jsonObj coreBD::testOBJ()
{
    string json = "{error:null, message:None, errorMessage:MoreNone}";
    jsonObj b(json);
    return b; //It fails here if I return a nested class with a rapidjson::Document in it. Returning NULL works
}

EDIT:

New question continuing solving this: Perform a copy of Document object of rapidjson

回答1:

Looking at the error it appears that the function returning the jsonObj is doing some kind of a copy or move construction as a part of returning the value and the underlying classes do not allow this probably by making those constructors private members.

There are classes whose design requires that a copy or assignment is prohibited in order to prevent memory leaks or because the objects are singleton type objects and only one version of the object is allowed.

Looking at this documentation on rapidjson there is a note in the section on Move semantics that may be pertinent. It looks like they are preventing a Copy in order to improve performance.

回答2:

jsonObj doesn't have copy constructor and it can't have any copy constructor since Document's copy constructor is disabled in rapidjson. Try to hold pointer to document instead, something like this :

class jsonObj {
    string jsonStr;
    string message;
    Document* doc; //HERE IS THE PROBLEM
    bool validMsg;
}

Or pass document(jsonObj) from outside to:

jsonObj query(string sSQL);

For example:

query(string sSQL, jsonObj & out_obj)

来源：https://stackoverflow.com/questions/22682513/lnk2019-unresolved-external-symbol-with-rapidjson

标签

c++

visual-c++

visual-studio-2012

rapidjson