The class styles define additional elements of the window class. Two or more styles can be combined by using the bitwise OR (|) operator. To assign a style to a window class, assign the style to the style member of the WNDCLASSEX structure. The class styles are as follows.
| Style | Action |
| CS_BYTEALIGNCLIENT | Aligns the window's client area on a byte boundary (in the x direction) to enhance performance during drawing operations. This style affects the width of the window and its horizontal placement on the display. |
| CS_BYTEALIGNWINDOW | Aligns the window on a byte boundary (in the x direction) to enhance performance during operations that involve moving or sizing the window. This style affects the width of the window and its horizontal placement on the display. |
| CS_CLASSDC | Allocates one device context to be shared by all windows in the class. For more information about device contexts, see Class and Private Device Contexts and Device Contexts. |
| CS_DBLCLKS | Instructs Windows to send a double-click message to the window procedure when the user double-clicks the mouse while the cursor is within a window belonging to the class. For more information about double-clicks, see Mouse Input. |
| CS_GLOBALCLASS | Specifies that the window class is an application global class. For more information, see Application Global Classes. |
| CS_HREDRAW | Specifies that the entire window is to be redrawn if a movement or size adjustment changes the width of the client area. |
| CS_NOCLOSE | Disables the Close command on the System menu. |
| CS_OWNDC | Allocates a unique device context for each window in the class. For more information about device contexts, see Class and Private Device Contexts and Device Contexts. |
| CS_PARENTDC | Sets the clipping rectangle of the child window to that of the parent window so that the child can draw on the parent. A window with the CS_PARENTDC style bit receives a regular device context from the system's cache of device contexts. It does not give the child the parent's device context or device context settings. Specifying CS_PARENTDC enhances an application's performance. For more information about device contexts, see Class and Private Device Contexts and Device Contexts. |
| CS_SAVEBITS | Saves, as a bitmap, the portion of the screen image obscured by a window. Windows uses the saved bitmap to re-create the screen image when the window is removed. Windows displays the bitmap at its original location and does not send WM_PAINT messages to windows obscured by the window if other screen actions have not invalidated the stored image. Use this style for small windows that are displayed briefly and then removed before other screen activity takes place (for example, menus or dialog boxes). This style increases the time required to display the window, because the operating system must first allocate memory to store the bitmap. |
| CS_VREDRAW | Specifies that the entire window is to be redrawn if a movement or size adjustment changes the height of the client area. |