string is not declared in this scope C++

Question

I have been testing out some gdi functions, and wanted to test out something with strings. However for some reason when I run this program I get the following error: 'string' was not declared in this scope

I even tried to include the "using namespace std" in the beginning (which usually I don't have to do in order to create strings) but in that case, after declaring std::string myString; I get another error saying: error: 'string' is not a member of 'std'

what could I be doing wrong? The complete code is here:

#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);

//++++++++++++++++++++HERE IS WHERE MY ERROR IS HAPPENING:

                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

Correcting the error

For your declaration to compile, you must include the standard header and address the right namespace:

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

Use of C++ strings with the Windows API

Using this string in relation with windows api, requires to pass argument mystring.c_str(), for a pointer to the null terminated c-string that the API expects:

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

Caution: this might be tricky : depending on the compiling options (see here), you may have to use std::wstring instead of std::string.

C++ strings that always work

For a heavy use of strings in winAPI code consider using the following type:

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

It can then be used in C++ code like a normal string/wstring and will adapt to any compiling options, provided that litterals use the practice of the WinAPI native code with TCHAR and TEXT(). Example:

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

Answer 2

std::string lives in string header. You might want to actually #include <string> before trying to use it.