SetWindowText

SetWindowText is a Windows API function used to change the text associated with a window or control. It is part of the User32 library and can modify a window’s caption (title bar) or the text displayed by a child control such as a button, edit box, or static text. In code, SetWindowText is commonly called to update user interface labels or titles at runtime.

The function has two parameters: a handle to the window or control (hWnd) and a string (lpString) containing the new text. If lpString is NULL, the function sets the text to an empty string. There are two concrete versions for ANSI and Unicode builds: SetWindowTextA and SetWindowTextW, with a macro alias SetWindowText that resolves to one of the two depending on the project settings.

SetWindowText sends a WM_SETTEXT message to the specified window. The window procedure for that class processes the message and updates the displayed text accordingly. For top-level windows, this updates the window caption; for child controls, it changes the text displayed by the control. Whether the text is accepted and how it is displayed can depend on the window class and the control type.

Return value and error handling: the function returns a nonzero value (TRUE) on success and zero (FALSE) on failure. When it fails, extended information can be retrieved with GetLastError. Possible failure scenarios include invalid window handles, unsupported window classes, insufficient memory, or attempts to modify a read-only or otherwise restricted control.

See also: WM_SETTEXT, GetWindowText, and related control text functions. SetWindowText is widely used in GUI applications to reflect changes in state, user actions, or programmatic updates to the interface.