GetWindowText() in Win32 C++ is not working - c++

Question

following code is not working .i am trying to get text from edit control but it does not work.m tired by trying all possible codes looking documentation on msdn etc...
case WM_COMMAND:
switch(LOWORD(wParam)){
case 1:
::MessageBox(hwnd,"button clicked","message",MB_OK);
break;
case 2:
TCHAR t[20]; //
GetWindowText(text_box,t,19);// this is not working????????????????
::MessageBox(hwnd,t,t,MB_OK);
cout<<t;
break;
for refrence below is the complete code :
#include <windows.h>
#include<iostream>
using namespace std;
const char g_szClassName[] = "myWindowClass";
// Step 4: the Window Procedure
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
HWND text_field, button , text_box;
char text_saved[20];
switch(msg)
{ case WM_CREATE:
text_field = CreateWindow("STATIC",
"Hello World",
WS_VISIBLE | WS_CHILD | WS_BORDER,
20,20, 90,25,
hwnd,
NULL,NULL,NULL);
button = CreateWindow("BUTTON",
"push button",
WS_VISIBLE | WS_CHILD | WS_BORDER,
20,50, 100,20,
hwnd,
(HMENU)1,NULL,NULL
) ;
text_box = CreateWindow("EDIT",
" ",
WS_VISIBLE | WS_CHILD | WS_BORDER,
20,80, 200,25,
hwnd,
NULL,NULL,NULL
);
CreateWindow("BUTTON",
"Save",
WS_VISIBLE | WS_CHILD | WS_BORDER,
20,120, 100,20,
hwnd,
(HMENU)2,NULL,NULL
);
break;
case WM_COMMAND:
switch(LOWORD(wParam)){
case 1:
::MessageBox(hwnd,"button clicked","message",MB_OK);
break;
case 2:
TCHAR t[20];
GetWindowText(text_box,t,19);
::MessageBox(hwnd,t,t,MB_OK);
cout<<t;
break;
}
break;
case WM_CLOSE:
DestroyWindow(hwnd);
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hwnd, msg, wParam, lParam);
}
return 0;
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
LPSTR lpCmdLine, int nCmdShow)
{
WNDCLASSEX wc;
HWND hwnd;
MSG Msg;
//Step 1: Registering the Window Class
wc.cbSize = sizeof(WNDCLASSEX);
wc.style = 0;
wc.lpfnWndProc = WndProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = hInstance;
wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
wc.lpszMenuName = NULL;
wc.lpszClassName = g_szClassName;
wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);
if(!RegisterClassEx(&wc))
{
MessageBox(NULL, "Window Registration Failed!", "Error!",
MB_ICONEXCLAMATION | MB_OK);
return 0;
}
// Step 2: Creating the Window
hwnd = CreateWindowEx(
WS_EX_CLIENTEDGE,
g_szClassName,
"The title of my window",
WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, CW_USEDEFAULT, 500,500,
NULL, NULL, hInstance, NULL);
if(hwnd == NULL)
{
MessageBox(NULL, "Window Creation Failed!", "Error!",
MB_ICONEXCLAMATION | MB_OK);
return 0;
}
ShowWindow(hwnd, nCmdShow);
UpdateWindow(hwnd);
// Step 3: The Message Loop
while(GetMessage(&Msg, NULL, 0, 0) > 0)
{
TranslateMessage(&Msg);
DispatchMessage(&Msg);
}
return Msg.wParam;
}

Answer 1

You've defined text_box (and the other variables) as local to the WndProc function, meaning their values are lost every time that function is called to process a message. You need to move them outside of the function scope (or make them static) if you want to preserve their values from one message to the next.

Answer 2

This is a working reworked version of your code, replacing the local variable text_box (which doesn't retain information from one call to the next) with a numerical control id and use of GetDlgItem, changing from ANSI to Unicode text, and fixing some other stuff, while mainly keeping the formatting:
#undef UNICODE
#define UNICODE
#include <windows.h>
#include<iostream>
#include <string>
using namespace std;
namespace g {
const auto class_name = L"myWindowClass";
const auto push_button_id = 1;
const auto save_button_id = 2;
const auto edit_field_id = 3;
const auto h_instance = ::GetModuleHandle( nullptr );
} // namespace g
// Step 4: the Window Procedure
void create_controls( const HWND hwnd )
{
CreateWindow( L"STATIC",
L"Hello World",
WS_VISIBLE | WS_CHILD | WS_BORDER,
20,20, 90,25,
hwnd,
nullptr, g::h_instance, nullptr );
CreateWindow( L"BUTTON",
L"push button",
WS_VISIBLE | WS_CHILD | WS_BORDER,
20,50, 100,20,
hwnd,
(HMENU) g::push_button_id, g::h_instance, nullptr
) ;
CreateWindow( L"EDIT",
L"",
WS_VISIBLE | WS_CHILD | WS_BORDER,
20,80, 200,25,
hwnd,
(HMENU) g::edit_field_id, g::h_instance, nullptr
);
CreateWindow( L"BUTTON",
L"Save",
WS_VISIBLE | WS_CHILD | WS_BORDER,
20,120, 100,20,
hwnd,
(HMENU) g::save_button_id, g::h_instance, nullptr
);
}
LRESULT CALLBACK WndProc( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam )
{
switch(msg)
{
case WM_CREATE:
create_controls( hwnd );
break;
case WM_COMMAND:
switch(LOWORD(wParam)) {
case 1:
::MessageBox( hwnd, L"button clicked", L"message", MB_SETFOREGROUND );
break;
case 2:
const HWND text_box = GetDlgItem( hwnd, g::edit_field_id );
const int n = GetWindowTextLength( text_box );
wstring text( n + 1, L'#' );
if( n > 0 )
{
GetWindowText( text_box, &text[0], text.length() );
}
text.resize( n );
::MessageBox(hwnd, text.c_str(), L"The text:", MB_SETFOREGROUND );
break;
}
break;
case WM_CLOSE:
DestroyWindow(hwnd);
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hwnd, msg, wParam, lParam);
}
return 0;
}
int main()
{
//Step 1: Registering the Window Class
WNDCLASSEX wc = { sizeof( WNDCLASSEX ) };
wc.style = 0;
wc.lpfnWndProc = WndProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = g::h_instance;
wc.hIcon = LoadIcon(nullptr, IDI_APPLICATION);
wc.hCursor = LoadCursor(nullptr, IDC_ARROW);
wc.hbrBackground = reinterpret_cast<HBRUSH>(COLOR_WINDOW+1);
wc.lpszMenuName = nullptr;
wc.lpszClassName = g::class_name;
wc.hIconSm = LoadIcon(nullptr, IDI_APPLICATION);
if(!RegisterClassEx(&wc))
{
MessageBox(nullptr, L"Window Registration Failed!", L"Error!",
MB_ICONEXCLAMATION | MB_SETFOREGROUND );
return E_FAIL;
}
// Step 2: Creating the Window
const HWND hwnd = CreateWindowEx(
WS_EX_CLIENTEDGE,
g::class_name,
L"The title of my window",
WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, CW_USEDEFAULT, 500,500,
nullptr, nullptr, g::h_instance, nullptr);
if(hwnd == nullptr)
{
MessageBox(nullptr, L"Window Creation Failed!", L"Error!",
MB_ICONEXCLAMATION | MB_SETFOREGROUND);
return E_FAIL;
}
ShowWindow(hwnd, SW_SHOWDEFAULT); // Note: any other value is replaced.
UpdateWindow(hwnd); // Not strictly necessary.
// Step 3: The Message Loop
MSG Msg;
int get_message_result;
while( (get_message_result = GetMessage(&Msg, nullptr, 0, 0)) > 0 )
{
TranslateMessage(&Msg);
DispatchMessage(&Msg);
}
return (get_message_result < 0? E_FAIL : Msg.wParam);
}