I'm learning to write basic Win32 apps in C and am trying to pass typed text from one editable textbox to a new window after pressing a button.
I noticed that the default text buffer capacity for such a transfer is 20 characters in Visual Studio 2019 (I am on 64-bit Windows 10). After I try to pass a string longer than 20 characters, I get an exception thrown.
I would like to know how to increase that buffer capacity, since eventually I want to be able to pass a filepath into the text input window and open that file.
My code:
#include <windows.h>
#include <string>
#include <iostream>
//lresult callback prototype
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam);
//window handles
HWND hMainWindow;
HINSTANCE hMainInstance;
HWND hLblOutput;
HWND hTxtInput;
HWND hButton;
#define IDC_TEXTBOX 1000
#define IDC_BUTTON 1001
//call to winmain - equivalent of main for win32 environments
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
MSG msg = { 0 };
WNDCLASS wc = { 0 };
wc.lpfnWndProc = WndProc;
wc.hInstance = hInstance;
wc.hbrBackground = (HBRUSH)(COLOR_BACKGROUND);
wc.lpszClassName = TEXT("NiceWindowsApp");
if (!RegisterClass(&wc))
return 1;
hMainWindow = CreateWindow(wc.lpszClassName, TEXT("My Windows Application"), WS_OVERLAPPEDWINDOW | WS_VISIBLE, 0, 0, 640, 480, 0, 0, hInstance, NULL);
hMainInstance = wc.hInstance;
while (GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return 0;
}
//callback definition
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
int offset = 0;
switch (message) {
case WM_CREATE:
hMainWindow = hWnd;
hTxtInput = CreateWindowEx(WS_EX_CLIENTEDGE, TEXT("EDIT"), TEXT("Type something here"),
WS_VISIBLE | WS_CHILD | ES_LEFT, 50, 50, 400, 25, hWnd,
(HMENU)IDC_TEXTBOX, hMainInstance, NULL);
hButton = CreateWindowEx(WS_EX_CLIENTEDGE, TEXT("BUTTON"), TEXT("Press Me!"), WS_VISIBLE | WS_CHILD | WM_COPY | ES_LEFT, 500, 30, 100, 60, hWnd,
(HMENU)IDC_BUTTON, hMainInstance, NULL);
break;
case WM_COMMAND:
if (LOWORD(wParam) == IDC_BUTTON)
{
//CANNOT HANDLE MORE THAN 20 CHARACTERS!!!
std::string input;
GetWindowTextA(hTxtInput, reinterpret_cast<char*> ((char*)input.c_str()), 400);
offset;
hLblOutput = CreateWindowEx(WS_EX_STATICEDGE, TEXT("EDIT"), input.c_str(), WS_VISIBLE | WS_CHILD | ES_READONLY | ES_LEFT, 50, 200 offset * 26, 800, 25, hWnd,
(HMENU)IDC_TEXTBOX, hMainInstance, NULL);
}
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}
I have tried to increase the third parameter in GetWindowTextA() to various numbers up to 4000, but it didn't seem to help.
CodePudding user response：
One correct way to do this is:
std::wstring text;
text.resize(GetWindowTextLengthW(hTxtInput));
text.resize(GetWindowTextW(hTxtInput, text.data(), text.size() 1));
CodePudding user response：
Solved as per the below:
#include <windows.h>
#include <string>
#include <iostream>
//lresult callback prototype
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam);
//window handles
HWND hMainWindow;
HINSTANCE hMainInstance;
HWND hLblOutput;
HWND hTxtInput;
HWND hButton;
CHAR s_text_1[]{ "Some text.." };
CHAR s_text_2[]{ 0 };
#define IDC_TEXTBOX 1000
#define IDC_BUTTON 1001
//call to winmain - equivalent of main for win32 environments
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
MSG msg = { 0 };
WNDCLASS wc = { 0 };
wc.lpfnWndProc = WndProc;
wc.hInstance = hInstance;
wc.hbrBackground = (HBRUSH)(COLOR_BACKGROUND);
wc.lpszClassName = TEXT("NiceWindowsApp");
if (!RegisterClass(&wc))
return 1;
hMainWindow = CreateWindow(wc.lpszClassName, TEXT("My Windows Application"), WS_OVERLAPPEDWINDOW | WS_VISIBLE,
0, 0, 640, 480, 0, 0, hInstance, NULL);
hMainInstance = wc.hInstance;
while (GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return 0;
}
//callback definition
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
int offset = 0;
switch (message) {
case WM_CREATE:
hMainWindow = hWnd;
hTxtInput = CreateWindowEx(WS_EX_CLIENTEDGE, TEXT("EDIT"), s_text_1,
WS_VISIBLE | WS_CHILD | ES_LEFT, 50, 50, 400, 25, hWnd,
(HMENU)IDC_TEXTBOX, hMainInstance, NULL);
hButton = CreateWindowEx(WS_EX_CLIENTEDGE, TEXT("BUTTON"), TEXT("Press Me!"), WS_VISIBLE | WS_CHILD | WM_COPY | ES_LEFT, 500, 30, 100, 60, hWnd,
(HMENU)IDC_BUTTON, hMainInstance, NULL);
break;
case WM_COMMAND:
if (LOWORD(wParam) == IDC_BUTTON)
{
//CANNOT HANDLE MORE THAN 20 CHARACTERS!!!
std::wstring input;
//GetWindowTextW(hTxtInput, reinterpret_cast<char*> ((char*)input.c_str()), 400);
int lgth = GetWindowTextLength(hTxtInput);
//GetWindowTextW(hTxtInput, reinterpret_cast<wchar_t*> ((wchar_t*)input.c_str()), lgth);
//GetWindowTextA(hTxtInput, char[], 400);
GetWindowText(hTxtInput, s_text_1, 255);
offset;
hLblOutput = CreateWindowEx(WS_EX_STATICEDGE, TEXT("EDIT"), s_text_1, WS_VISIBLE | WS_CHILD | ES_READONLY | ES_LEFT, 50, 200 offset * 26, 800, 25, hWnd,
(HMENU)IDC_TEXTBOX, hMainInstance, NULL);
SetWindowText(hLblOutput, s_text_1);
}
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}
Thanks for your hints everybody.
EDIT: I now realise that this solution is not technically perfect and can lead to undefined behaviour and/or memory leaks. I'll take the advice presented in the other answers and comments into account and adjust the code accordingly.