Unresolved External Symbol with Template Function Only When Used

Question

I have been getting the :unresolved external symbol "public static int __cdecl Memory::Read (unsigned __int64,unsigned __int64_" for my declaration of a template function "Read"

It is defined in a class known as "memory" with the header file:

#ifndef MEMORY_H
#define MEMORY_H

#include <string>
#include "DataFuncs.h"

using namespace std;

  class Memory {

    public:
        template <typename type>
        static type Read(DWORD64 Address, SIZE_T size);
        static bool Write(DWORD64 Address, uintptr_t Value, SIZE_T size);       
  };

#endif

Its .cpp definition is the following:

#include "Memory.h"

template <typename type>
type Memory::Read(DWORD64 Address, SIZE_T size) {
    return Data.Read<type>(Process_ID, Address, size);
}

bool Memory::Write(DWORD64 Address, uintptr_t Value, SIZE_T size) {

    if (Data.Write(Address, Value, size))
        return true;
    return false;
}

The error does not occur until it is actually used in a different file. Its implementation is as follows:

#include "Memory.h"
#include "Special_Functions.h"

__int32 Special_Functions::Test(){

    __int32 x = Memory::Read<__int32>(0x20302, sizeof(__int32));
    return x;
}

If I take away the Memory::Read<__int32>(0x20302, sizeof(__int32)); line and just type return 53 then no compiling problems occur. Any idea why and how to fix it? Thanks!

You need to define (not just declare) the template functions in the header — UnholySheep, Jul 15 '17 at 14:32
Templates must be implemented in headers. The compiler needs to see the actual implementation at the point where the template is instantiated. — Igor Tandetnik, Jul 15 '17 at 14:32
Strictly saying, not *must*, but *should*. It's possible to hide implementation into a .cpp, but you'd have to list all types this template has to work with in the same .cpp. — HolyBlackCat, Jul 15 '17 at 14:39

Unresolved External Symbol with Template Function Only When Used

0 Answers0