在 Visual Studio 2019 中通过 Windows 桌面向导使用 C++ 标准库

Question

我正在关注教程here。

这是我正在使用的代码，从该站点复制而来：

#include <windows.h>
#include <stdlib.h>
#include <string.h>
#include <tchar.h>

// Global variables

// The main window class name.
static TCHAR szWindowClass[] = _T("DesktopApp");

// The string that appears in the application's title bar.
static TCHAR szTitle[] = _T("Windows Desktop Guided Tour Application");

HINSTANCE hInst;

// Forward declarations of functions included in this code module:
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain(
   _In_ HINSTANCE hInstance,
   _In_opt_ HINSTANCE hPrevInstance,
   _In_ LPSTR     lpCmdLine,
   _In_ int       nCmdShow
)
{
   WNDCLASSEX wcex;

   wcex.cbSize = sizeof(WNDCLASSEX);
   wcex.style          = CS_HREDRAW | CS_VREDRAW;
   wcex.lpfnWndProc    = WndProc;
   wcex.cbClsExtra     = 0;
   wcex.cbWndExtra     = 0;
   wcex.hInstance      = hInstance;
   wcex.hIcon          = LoadIcon(wcex.hInstance, IDI_APPLICATION);
   wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);
   wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1);
   wcex.lpszMenuName   = NULL;
   wcex.lpszClassName  = szWindowClass;
   wcex.hIconSm        = LoadIcon(wcex.hInstance, IDI_APPLICATION);

   if (!RegisterClassEx(&wcex))
   {
      MessageBox(NULL,
         _T("Call to RegisterClassEx failed!"),
         _T("Windows Desktop Guided Tour"),
         NULL);

      return 1;
   }

   // Store instance handle in our global variable
   hInst = hInstance;

   // The parameters to CreateWindowEx explained:
   // WS_EX_OVERLAPPEDWINDOW : An optional extended window style.
   // szWindowClass: the name of the application
   // szTitle: the text that appears in the title bar
   // WS_OVERLAPPEDWINDOW: the type of window to create
   // CW_USEDEFAULT, CW_USEDEFAULT: initial position (x, y)
   // 500, 100: initial size (width, length)
   // NULL: the parent of this window
   // NULL: this application does not have a menu bar
   // hInstance: the first parameter from WinMain
   // NULL: not used in this application
   HWND hWnd = CreateWindowEx(
      WS_EX_OVERLAPPEDWINDOW,
      szWindowClass,
      szTitle,
      WS_OVERLAPPEDWINDOW,
      CW_USEDEFAULT, CW_USEDEFAULT,
      500, 100,
      NULL,
      NULL,
      hInstance,
      NULL
   );

   if (!hWnd)
   {
      MessageBox(NULL,
         _T("Call to CreateWindow failed!"),
         _T("Windows Desktop Guided Tour"),
         NULL);

      return 1;
   }

   // The parameters to ShowWindow explained:
   // hWnd: the value returned from CreateWindow
   // nCmdShow: the fourth parameter from WinMain
   ShowWindow(hWnd,
      nCmdShow);
   UpdateWindow(hWnd);

   // Main message loop:
   MSG msg;
   while (GetMessage(&msg, NULL, 0, 0))
   {
      TranslateMessage(&msg);
      DispatchMessage(&msg);
   }

   return (int) msg.wParam;
}

//  FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
//  PURPOSE:  Processes messages for the main window.
//
//  WM_PAINT    - Paint the main window
//  WM_DESTROY  - post a quit message and return
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
   PAINTSTRUCT ps;
   HDC hdc;
   TCHAR greeting[] = _T("Hello, Windows desktop!");

   switch (message)
   {
   case WM_PAINT:
      hdc = BeginPaint(hWnd, &ps);

      // Here your application is laid out.
      // For this introduction, we just print out "Hello, Windows desktop!"
      // in the top left corner.
      TextOut(hdc,
         5, 5,
         greeting, _tcslen(greeting));
      // End application-specific layout section.

      EndPaint(hWnd, &ps);
      break;
   case WM_DESTROY:
      PostQuitMessage(0);
      break;
   default:
      return DefWindowProc(hWnd, message, wParam, lParam);
      break;
   }

   return 0;
}

我现在想根据自己的需要修改程序，例如使用<vector> 和<fstream>。

但是，当我包含 fstream 并尝试将 fstream 对象声明为全局变量或在 winMain 函数中时，我收到以下错误：identifier fstream is undefined。 <vector> 也是如此。但是，包含cmath 然后使用cos 函数不会导致任何问题。

Answer 1

您必须包含using namespace std; 的指令。这样fstream 将被编译器识别，因为它属于std 命名空间。否则，您必须编写 std::fstream 才能访问此类。