在此作用域C++中未声明字符串

Question

我一直在测试一些gdi函数，并且想用字符串测试一些东西。然而，由于某些原因，当我运行这个程序时，我得到了以下错误：'string‘没有在这个作用域中声明

我甚至尝试在开头包含“使用命名空间std”(通常我不需要这样做就可以创建字符串)，但在这种情况下，在声明std::string myString之后，我得到另一个错误: error：'string‘不是'std’的成员

我能做错什么呢？完整的代码在这里：

#define _WIN32_WINNT    0x0500  

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


LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);

TCHAR szClassName[ ] = _T("CodeBlocksWindowsApp");

int WINAPI WinMain (HINSTANCE hThisInstance,
                 HINSTANCE hPrevInstance,
                 LPSTR lpszArgument,
                 int nCmdShow)
{
HWND hwnd;               /* This is the handle for our window */
MSG messages;            /* Here messages to the application are saved */
WNDCLASSEX wincl;        /* Data structure for the windowclass */

/* The Window structure */
wincl.hInstance = hThisInstance;
wincl.lpszClassName = szClassName;
wincl.lpfnWndProc = WindowProcedure;      /* This function is called by windows */
wincl.style = CS_DBLCLKS;                 /* Catch double-clicks */
wincl.cbSize = sizeof (WNDCLASSEX);

/* Use default icon and mouse-pointer */
wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
wincl.hCursor = LoadCursor (NULL, IDC_ARROW);
wincl.lpszMenuName = NULL;                 /* No menu */
wincl.cbClsExtra = 0;                      /* No extra bytes after the window class */
wincl.cbWndExtra = 0;                      /* structure or the window instance */
/* Use Windows's default colour as the background of the window */
wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND;

/* Register the window class, and if it fails quit the program */
if (!RegisterClassEx (&wincl))
    return 0;

/* The class is registered, let's create the program*/
hwnd = CreateWindowEx (
       WS_EX_LAYERED,// | WS_EX_TRANSPARENT,                   /* Extended possibilites      for variation */
       szClassName,         /* Classname */
       _T("Code::Blocks Template Windows App"),       /* Title Text */
       WS_OVERLAPPEDWINDOW, /* default window */
       CW_USEDEFAULT,       /* Windows decides the position */
       CW_USEDEFAULT,       /* where the window ends up on the screen */
       544,                 /* The programs width */
       375,                 /* and height in pixels */
       HWND_DESKTOP,        /* The window is a child-window to desktop */
       NULL,                /* No menu */
       hThisInstance,       /* Program Instance handler */
       NULL                 /* No Window Creation data */
       );


COLORREF greyishColor = RGB(212, 208, 200);
SetLayeredWindowAttributes(hwnd, greyishColor, 0, LWA_COLORKEY);

/* Make the window visible on the screen */
ShowWindow (hwnd, 3);//nCmdShow);



                HDC hdc;
                hdc = GetDC(hwnd);
                //drawing a rectangle
                    Rectangle(hdc, 100, 100, 200, 300);


                ReleaseDC(hwnd, hdc);


                ///again doing the hdc bit
                hdc = GetDC(hwnd);
                HPEN hPenOld;


                HPEN hLinePen;
                COLORREF qLineColor = RGB(255, 0 , 0);
                hLinePen = CreatePen(PS_SOLID, 7, qLineColor);
                hPenOld = (HPEN)SelectObject(hdc, hLinePen);

                MoveToEx(hdc, 100, 100, NULL);
                LineTo(hdc, 500, 250);

                SelectObject(hdc, hPenOld);
                DeleteObject(hLinePen);

                ///again releasing
                ReleaseDC(hwnd, hdc);

//+这里是我的错误所在：

                string myString;


/* Run the message loop. It will run until GetMessage() returns 0 */
while (GetMessage (&messages, NULL, 0, 0))
{
    /* Translate virtual-key messages into character messages */
    TranslateMessage(&messages);
    /* Send message to WindowProcedure */
    DispatchMessage(&messages);
}

/* The program return-value is 0 - The value that PostQuitMessage() gave */
return messages.wParam;
}


/*  This function is called by the Windows function DispatchMessage()  */

LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)                  /* handle the messages */
    {
        case WM_DESTROY:
            PostQuitMessage (0);       /* send a WM_QUIT to the message queue */
            break;
        default:                      /* for messages that we don't deal with */
            return DefWindowProc (hwnd, message, wParam, lParam);
    }

    return 0;
}

Answer 1

std::string位于string报头中。在尝试使用它之前，您可能想要实际使用#include <string>。

Answer 2

要使您的声明得到认可，您必须

#include <string>
using std::string;     // (or using namespace std if you want to use more of std.)  

如果你想在windows api中使用这个字符串，你必须传递参数mystring.c_str()来获得一个指向空值终止的c字符串的指针：

MessageBox(NULL, mystring.c_str(), TEXT("Attention !"), MB_OK); 

另外，要小心:根据您的编译选项(参见here)，您可能必须使用std::string或std::wstring。

如果您希望在windows程序中大量使用字符串，但又希望代码独立于unicode设置进行编译，例如使用TCHAR和TEXT()，则可以选择以下类型定义：

typedef std::basic_string<TCHAR> tstring;  // based on microsoft's TCHAR 

然后，您可以根据编译选项将其用作普通字符串/wstring：

tstring s, t( TEXT("Hello"));
s = t + TEXT(" world !");