C++ and WinApi - usage of GetWindowText() to get parameters for C++ code

Question

I have coded some C++ console program which converts one filetype to another. I need to turn the console application into a window one. I have never made window applications. I have chosen WinApi, because I don't have much time and don't want to change IDE (DEV C++ 5.10), compiler/linker settings etc. I need a small simple window. Parameters I need to get from the user are: path for input file, name and path for output file, and two parameters of type double. I have started to experiment, and wanted to put the text from window to a .txt file. The problem is what I get in the .txt file. My code:

#include <windows.h>
#include <string>
#include <fstream>
#include <iostream>

using namespace std;

HWND g_hText;

LRESULT CALLBACK WndProc(HWND hwnd, UINT Message, WPARAM wParam, LPARAM lParam) {
    switch(Message) {

        case WM_CLOSE:
        {
            DestroyWindow( hwnd );
        }
        break;

        case WM_DESTROY: {
            PostQuitMessage(0);
            break;
        }

        //here I create the file and write to it
        case WM_COMMAND:
        {   if(( HWND ) lParam == g_hText )
            {   DWORD dlugosc = GetWindowTextLength( g_hText );
                LPSTR Bufor =( LPSTR ) GlobalAlloc( GPTR, dlugosc + 1 );
                GetWindowText( g_hText, Bufor, dlugosc + 1 );

                ofstream out("some_file.txt",ios_base::app);
                out<<Bufor;
                out.close();
            }
            break;  
        }

        default:
            return DefWindowProc(hwnd, Message, wParam, lParam);

        }

    return 0;
    }

    MSG msg;

    int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) {
    WNDCLASSEX wc;
    HWND hwnd;

    memset(&wc,0,sizeof(wc));//sprawdzic co to
    wc.cbSize        = sizeof(WNDCLASSEX);
    wc.style         = 0;
    wc.lpfnWndProc   = WndProc;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra = 0;
    wc.hInstance     = hInstance;
    wc.hCursor       = LoadCursor(NULL, IDC_ARROW);

    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
    wc.lpszMenuName  = NULL;
    wc.lpszClassName = "WindowClass";
    wc.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
    wc.hIconSm       = LoadIcon(NULL, IDI_APPLICATION);

    if(!RegisterClassEx(&wc)) {
        MessageBox(NULL, "Window Registration Failed!","Error!",MB_ICONEXCLAMATION|MB_OK);
        return 0;
    }

    hwnd = CreateWindowEx(WS_EX_CLIENTEDGE,"WindowClass","Caption",WS_VISIBLE|WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        640,
        480,
        NULL,NULL,hInstance,NULL);

    if(hwnd == NULL) {
        MessageBox(NULL, "Window Creation Failed!","Error!",MB_ICONEXCLAMATION|MB_OK);
        return 0;
    }

    g_hText = CreateWindowEx( WS_EX_CLIENTEDGE, "EDIT", NULL, WS_CHILD | WS_VISIBLE | WS_BORDER,
    200, 0, 150, 30, hwnd, NULL, hInstance, NULL );

    while(GetMessage(&msg, NULL, 0, 0) > 0) {
        TranslateMessage(&msg); 
        DispatchMessage(&msg);
    }

    return msg.wParam;
}

When I type, for example, "qwerty" in the text window, I get "qqqwqwqweqweqwerqwerqwertqwertqwertyqwertyqwerty" in the text file. The text from the window is being read continually. I was trying to make it being read after pressing "Enter"

case WM_COMMAND:
{   if(( HWND ) lParam == g_hText )
    {    if(WM_KEYDOWN)
        {    if(VK_RETURN)
            {   DWORD dlugosc = GetWindowTextLength( g_hText );
                LPSTR Bufor =( LPSTR ) GlobalAlloc( GPTR, dlugosc + 1 );
                GetWindowText( g_hText, Bufor, dlugosc + 1 );

                ofstream out("some_file.txt",ios_base::app);
                out<<Bufor;
                out.close();
            }
            break;  
        }

        default:
            return DefWindowProc(hwnd, Message, wParam, lParam);

        }
    }
}

but with no effect. How should it be done to be done properly?

I am confused about your mention of WM_KEYDOWN and VK_RETURN, since they show up nowhere in the code you posted. Are you actually using it somewhere in your code? — zenzelezz
– zenzelezz, Commented Jun 12, 2015 at 12:54
I have used it, but deleted it since it didn't work. I have edited the post. — beginner
– beginner, Commented Jun 12, 2015 at 13:07

ST3 · Accepted Answer · 2015-06-12 13:24:15Z

2

You need to properly handle WM_KEYDOWN, not WM_COMMAND, because windows receives WM_KEYDOWN after key is pressed and WM_COMMAND after variuos of events.

case WM_KEYDOWN:
{   
    if(wParam == VK_RETURN)
    {   
        DWORD dlugosc = GetWindowTextLength( g_hText );
        LPSTR Bufor =( LPSTR ) GlobalAlloc( GPTR, dlugosc + 1 );
        GetWindowText( g_hText, Bufor, dlugosc + 1 );

        ofstream out("some_file.txt",ios_base::app);
        out<<Bufor;
        out.close();
    }
    break;  
}

Also,

if(WM_KEYDOWN)
if(VK_RETURN)

These two lines basically are if (true) and don't forget to free allocated memory.

edited Jun 12, 2015 at 13:24

answered Jun 12, 2015 at 13:18

ST3

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3 Comments

beginner Over a year ago

Thank you; I misunderstood the basics, obviously.

Remy Lebeau Over a year ago

Do note that if the user holds the Return key down, you will get multiple WM_KEYDOWN messages with an incrementing repeat counter. So either handle WM_KEYUP instead, or change the app design. For a GUI app, it makes more sense to have the user press a button when ready to process entered input, don't process on individual keystrokes. You can detect that button press by handling the BN_CLICKED notification.

beginner Over a year ago

@RemyLebeau. Thank you for the tip. Pressing a button when ready sounds better for me, it seems to give clearer code. I'll try this design.

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