Tk_FreeFontFromObj(3) maintain database of fonts

Other Alias

Tk_AllocFontFromObj, Tk_GetFont, Tk_GetFontFromObj, Tk_NameOfFont, Tk_FreeFont


#include <tk.h>

Tk_AllocFontFromObj(interp, tkwin, objPtr)

Tk_GetFont(interp, tkwin, string)

Tk_GetFontFromObj(tkwin, objPtr)

CONST char *

Tk_FreeFontFromObj(tkwin, objPtr)



Tcl_Interp    *interp    (in)
Interpreter to use for error reporting. If NULL, then no error messages are left after errors.
Tk_Window    tkwin    (in)
Token for window in which font will be used.
Tcl_Obj    *objPtr    (in/out)
Gives name or description of font. See documentation for the font command for details on acceptable formats. Internal rep will be modified to cache corresponding Tk_Font.
const char    *string    (in)
Same as objPtr except description of font is passed as a string and resulting Tk_Font isn't cached.
Tk_Font    tkfont    (in)
Opaque font token.


Tk_AllocFontFromObj finds the font indicated by objPtr and returns a token that represents the font. The return value can be used in subsequent calls to procedures such as Tk_GetFontMetrics, Tk_MeasureChars, and Tk_FreeFont. The Tk_Font token will remain valid until Tk_FreeFontFromObj or Tk_FreeFont is called to release it. ObjPtr can contain either a symbolic name or a font description; see the documentation for the font command for a description of the valid formats. If Tk_AllocFontFromObj is unsuccessful (because, for example, objPtr did not contain a valid font specification) then it returns NULL and leaves an error message in interp's result if interp isn't NULL. Tk_AllocFontFromObj caches information about the return value in objPtr, which speeds up future calls to procedures such as Tk_AllocFontFromObj and Tk_GetFontFromObj.

Tk_GetFont is identical to Tk_AllocFontFromObj except that the description of the font is specified with a string instead of an object. This prevents Tk_GetFont from caching the matching Tk_Font, so Tk_GetFont is less efficient than Tk_AllocFontFromObj.

Tk_GetFontFromObj returns the token for an existing font, given the window and description used to create the font. Tk_GetFontFromObj doesn't actually create the font; the font must already have been created with a previous call to Tk_AllocFontFromObj or Tk_GetFont. The return value is cached in objPtr, which speeds up future calls to Tk_GetFontFromObj with the same objPtr and tkwin.

Tk_AllocFontFromObj and Tk_GetFont maintain a database of all fonts they have allocated. If the same font is requested multiple times (e.g. by different windows or for different purposes), then a single Tk_Font will be shared for all uses. The underlying resources will be freed automatically when no-one is using the font anymore.

The procedure Tk_NameOfFont is roughly the inverse of Tk_GetFont. Given a tkfont that was created by Tk_GetFont (or Tk_AllocFontFromObj), the return value is the string argument that was passed to Tk_GetFont to create the font. The string returned by Tk_NameOfFont is only guaranteed to persist until the tkfont is deleted. The caller must not modify this string.

When a font is no longer needed, Tk_FreeFontFromObj or Tk_FreeFont should be called to release it. For Tk_FreeFontFromObj the font to release is specified with the same information used to create it; for Tk_FreeFont the font to release is specified with its Tk_Font token. There should be exactly one call to Tk_FreeFontFromObj or Tk_FreeFont for each call to Tk_AllocFontFromObj or Tk_GetFont.