Unresolved External Symbol error because of a GetKeyState() call in struct method.

I'm currently in the process of learning C/C++ and I was just messing around with some projects I had in my head. This problem might be easy to fix but I have no idea about how C++ Works underneath So thats why i'm here now.

I have a header file with a Namespace, and inside of the namespace is a Struct with a few methods:

Code:

---

#pragma once

#include <iostream>
#include <Windows.h>

namespace IM {
  // Movement Controls ------------//
  const int MoveUp = VK_UP;    //-//
  const int MoveDown = VK_DOWN; //
  const int MoveLeft = VK_LEFT; //
  const int MoveRight = VK_RIGHT; //
  //-------------------------------//

  // Tekken Styled Action Buttons -//
  const int LeftPunch = 0x41;  //--//
  const int RightPunch = 0x53;  //--//
  const int LeftKick = 0x5A;    //--//
  const int RightKick = 0x58;  //--//
  //-------------------------------//

  // Start and Select. --------//
  const int Start = 0x44;      //
  const int Select = 0x43;      //
  //---------------------------//

  struct Instance {
    bool KeyHeld(int keyCode);
    bool KeyDown(int keyCode);
    bool KeyUp(int keyCode);
  };
}

---

Alongside this there is a .cpp file with the same name, Here's the code inside of it:

Code:

---

#include "InputManager.hpp"

using namespace IM;

bool Instance::KeyHeld(int KeyCode)
{
  if (GetKeyState(KeyCode) & 0x8000) {
    return true;
  }
}

bool Instance::KeyDown(int KeyCode)
{
  return true;
}

bool Instance::KeyUp(int KeyCode)
{
  return true;
}

---

And My main.cpp file looks as such:

Code:

---

#include "InputManager.hpp"

int main()
{
  IM::Instance InputManager;
  while (1) {
    if (InputManager.KeyHeld(IM::Start)) {
      std::cout << "Key Down." << std::endl;
    }
  }
}

---

This is the Output produced by Microsoft Compiler:

Attachment 15833

I'm using Visual Studio Code with C++ Extensions. Heres how the build.bat file looks like:

Code:

---

@echo off
if exist "C:\Program Files (x86)\Microsoft Visual Studio\2017\BuildTools\VC\Auxiliary\Build\vcvarsall.bat" (
    call "C:\Program Files (x86)\Microsoft Visual Studio\2017\BuildTools\VC\Auxiliary\Build\vcvarsall.bat" x86
) else (
    call "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvarsall.bat" x86
)
set compilerflags=/Od /Zi /EHsc /std:c++latest /I include
set linkerflags=/OUT:bin\main.exe
cl.exe %compilerflags% src\*.cpp /link %linkerflags%
del bin\*.ilk *.obj *.pdb

---

You need to link against the library that defines that windows function. According to the documentation, the library is User32.lib. I don't use windows so I'm not sure of the command line syntax, but maybe something like this:

Code:

---

set compilerflags=/Od /Zi /EHsc /std:c++latest /I include
set linkerflags=/OUT:bin\main.exe
set libraries=User32.lib
cl %compilerflags% %libraries% src\*.cpp /link %linkerflags%

---