Error LNK2001 when instantiating a class with parameters within a constructor

Question

Good afternoon,

Issue #1

I have a mysterious issue, where I can call a class I've defined without any issues, however if I try to add a parameter to the constructor, and instantiate the class with an argument, it gives two LNK2001 errors, one for the constructor and one for the destructor.

error LNK2001: unresolved external symbol "public: __thiscall socket_h::~socket_h(void)" (??1socket_h@@$$FQAE@XZ)
error LNK2001: unresolved external symbol "public: __thiscall socket_h::socket_h(char const *)" (??0socket_h@@$$FQAE@PBD@Z)

The code is as follows:

Class Header:

class socket_h{
protected:
    ;//...

public:

    socket_h(const char*);
    int receive_data(char* szBuffer);
    int send_data(char* szMessage);
    ~socket_h(void);
};

Class Source:

class socket_h{
protected: 

       ;//...

public:

socket_h()
{
    socket_h("192.168.5.100");
}

socket_h(const char* ip_address)
{
    ;//...;
}
//...
~socket_h(void)
{
    closesocket(sClient);

    WSACleanup();
}
};

Calling Function:

private: System::Void read_socket_Click(System::Object^  sender, System::EventArgs^  e) {
         socket_h accelerometer("192.168.5.100");

}

Issue #2

I have a follow up error.

I am still looking for help with the above issue, but in order to save time, I added an extra method to the class and changed my calling function to:

private: System::Void read_socket_Click(System::Object^  sender, System::EventArgs^  e) {

         socket_h accelerometer();
         accelerometer->setAddress("192.168.5.100", 80);
}

However, I now get the error:

error C2227: left of '->setAddress' must point to class/struct/union/generic type   1664    1

I seem to have done everything correctly, and I don't understand why this may be happening. Thank you.

Answer 1

You have the whole bunch of errors and misconceptions. Starting with Hello World program and reading some C++ tutorials would be good for you. Now to the problems.

Issue #1

You forgot to declare parameterless constructor in header file:

class socket_h {
  ...
  socket_h();
  ...
};

Your source file looks suspicious too. You shouldn't be using class socket_h { ... }; in source file anymore. Instead define methods and constructors using scope resolution operator :

socket_h::socket_h()
{

}

socket_h::socket_h(const char* ip_address)
{

}

socket_h::~socket_h(void)
{
    closesocket(sClient);

    WSACleanup();
}

Furthermore, you have semantic error with constructor chain call:

socket_h::socket_h()
{
    socket_h("192.168.5.100"); // <--- this is illegal
}

In C++11 you can use Delegating constructors as follows:

socket_h::socket_h(): socket_h("192.168.5.100")
{

}

However, this feature seems to be not implemented in VC++ 11 yet.

Issue #2

Change to:

socket_h accelerometer;

ie remove () . Otherwise, the compiler confuses it with parameterless function declaration, which would have name accelerometer and return type socket_h . This ambiguity issue is known as the most vexing problem .

Change to:

accelerometer.setAddress("192.168.5.100", 80);

Explanation is simple: accelerometer is not a pointer, therefore you should not be using -> to access its members and methods. accelerometer is an instance of socket_h , so to access its members and methods, you should use . operator.

Answer 2

socket_h accelerometer("192.168.5.100"); // You don't have a constructor that takes a string as an argument.