mask

Unsigned integer that specifies which other structure members contain valid data or must be filled in. It can be a combination of the following values.

Value	Description
HDI_BITMAP	The hbmmember is valid.
HDI_FORMAT	The fmtmember is valid.
HDI_HEIGHT	The cxymember is valid and specifies the width of the item.
HDI_IMAGE	The iImagemember is valid and specifies the image to be displayed with the item.
HDI_LPARAM	The lParammember is valid.
HDI_ORDER	The iOrdermember is valid and specifies the item's order value.
HDI_TEXT	The pszTextand cchTextMaxmembers are valid.
HDI_WIDTH	The cxymember is valid and specifies the width of the item.

cxy

Integer that contains the width of the item.

pszText

Pointer to a null-terminated item string. If this member is set to LPSTR_TEXTCALLBACK, the control will request text information for this item by using HDN_GETDISPINFOmessages.

hbm

Handle to the item bitmap.

cchTextMax

Integer that contains the length of the item string, in characters.

fmt

Set of bit flags that specify the item's format.

This member can include one of the following text justification or right-to-left (RTL) reading order bit flags.

Value	Description
HDF_CENTER	The item's contents are centered.
HDF_LEFT	The item's contents are left-aligned.
HDF_RIGHT	The item's contents are right-aligned.
HDF_RTLREADING	The header text will read in the opposite direction from the text in the parent window. Note: Typically, windows display text left-to-right (LTR). Windows can be mirrored to display languages such as Hebrew or Arabic that read right-to-left. Usually, header text is read in the same direction as the text in its parent window.

The preceding flag is combined with one of the following flags.

Value	Description
HDF_BITMAP	The item displays a bitmap.
HDF_BITMAP_ON_RIGHT	The bitmap appears to the right of text. This does not affect an image from an image list assigned to the header item.
HDF_OWNERDRAW	The header control's owner draws the item.
HDF_STRING	The item displays a string.

Additionally, the following flag can be combined with any of the preceding flags.

Value	Description
HDF_IMAGE	The item displays an image from an image list.
	You can use the HDF_JUSTIFYMASK mask to isolate the text justification portion of the fmtmember.

lParam

Application-defined item data.

iImage

Integer that contains a zero-based index of an image within the image list. The specified image will be displayed in the header item, in addition to any image specified in the hbmmember. If iImageis set to I_IMAGECALLBACK, the control requests text information for this item by using HDN_GETDISPINFO messages.

iOrder

Integer that contains the order in which the item appears within the header control, from left to right. That is, the value for the far left item is 0. The value for the next item to the right is 1, and so on.

The header control can display text, an image and a bitmap for an item all at the same time. The alignment flags determine the order in which they appear. With HDF_LEFT or HDF_CENTER, the order is image, text, and then bitmap. With HDF_RIGHT the order is bitmap, image and then text.

To define the dimensions of a header control, set the prcmember of the HDLAYOUTstructure to point to a RECTstructure that contains the dimensions that you want to use. You can only change the width of the header control at runtime.