MessageBox Function

int MessageBox(
    _In_opt_ HWND hWnd,
    _In_opt_ LPCSTR lpText,
    _In_opt_ LPCSTR lpCaption,
    _In_ UINT uType
);

The MessageBox function creates, displays, and operates a message box. A message box is a modal dialog box that displays a specified message to the user, along with a specified icon and set of buttons.

Parameters

hWnd

A handle to the owner window of the message box. This parameter can be NULL if the message box has no owner.

lpText

A pointer to a null-terminated string that contains the message to be displayed.

lpCaption

A pointer to a null-terminated string that contains the desired caption for the message box. If this parameter is NULL, the caption is set to "Error".

uType

The content and behavior of the message box. This parameter can be a combination of flags that define the appearance of the message box, including the icons displayed and the buttons available.

Return Value

int

If the function succeeds, the return value is one of the following integer values corresponding to the button that the user clicked: IDOK, IDCANCEL, IDABORT, IDRETRY, IDIGNORE, IDYES, or IDNO.
If the function fails (for example, because it cannot create the message box), the return value is 0.

Remarks

The MessageBox function can display various icons, such as information, warning, error, or question marks, by specifying appropriate flags in the uType parameter. It also supports different button combinations like OK, OK/Cancel, Yes/No, etc.

When a message box is displayed, the user must respond to it before the application can continue execution. This makes message boxes suitable for displaying critical information or prompting for user confirmation.

#include <windows.h>

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    int msgboxID = MessageBox(
        NULL,
        "This is the message text.",
        "My Application",
        MB_ICONWARNING | MB_YESNO | MB_DEFBUTTON2
    );

    switch (msgboxID)
    {
        case IDYES:
            // User clicked Yes
            break;
        case IDNO:
            // User clicked No
            break;
    }

    return 0;
}