WM_GETTEXT

The DefWindowProc function copies the text associated with the window into the specified buffer and returns the number of characters copied. Note, for non-text static controls this gives you the text with which the control was originally created, that is, the ID number. However, it gives you the ID of the non-text static control as originally created. That is, if you subsequently used a STM_SETIMAGE to change it the original ID would still be returned.

For an edit control, the text to be copied is the content of the edit control. For a combo box, the text is the content of the edit control (or static-text) portion of the combo box. For a button, the text is the button name. For other windows, the text is the window title. To copy the text of an item in a list box, an application can use the LB_GETTEXT message.

When the WM_GETTEXT message is sent to a static control with the SS_ICON style, a handle to the icon will be returned in the first four bytes of the buffer pointed to by lParam. This is true only if the WM_SETTEXT message has been used to set the icon.

Rich Edit: If the text to be copied exceeds 64K, use either the EM_STREAMOUT or EM_GETSELTEXT message.

Windows 2000: Sending a WM_GETTEXT message to a non-text static control, such as a static bitmap or static icon control, does not return a string value. Instead, it returns zero. In addition, in previous versions of Windows and Windows NT, applications could send a WM_GETTEXT message to a non-text static control to retrieve the control's ID. To retrieve a control's ID in Windows 2000, applications can use GetWindowLong passing GWL_ID as the index value or GetWindowLongPtr using GWLP_ID.

copied from PSDK 2000 (July Edition)

int GetWindowText( HWND hWnd, // handle of window or control with text LPTSTR lpString, // address of buffer for text int nMaxCount // maximum number of characters to copy );