XAllocClassHint (3) - Linux Manuals

XAllocClassHint: allocate class hints structure and set or read a window's WM_CLASS property


XAllocClassHint, XSetClassHint, XGetClassHint, XClassHint - allocate class hints structure and set or read a window's WM_CLASS property


XClassHint *XAllocClassHint(void);
XSetClassHint(Display *display, Window w, XClassHint *class_hints);
Status XGetClassHint(Display *display, Window w, XClassHint *class_hints_return);


Specifies the connection to the X server.
Specifies the XClassHint structure that is to be used.
Returns the XClassHint structure.
Specifies the window.


The XAllocClassHint function allocates and returns a pointer to a XClassHint structure. Note that the pointer fields in the XClassHint structure are initially set to NULL. If insufficient memory is available, XAllocClassHint returns NULL. To free the memory allocated to this structure, use XFree.

The XSetClassHint function sets the class hint for the specified window. If the strings are not in the Host Portable Character Encoding, the result is implementation-dependent.

XSetClassHint can generate BadAlloc and BadWindow errors.

The XGetClassHint function returns the class hint of the specified window to the members of the supplied structure. If the data returned by the server is in the Latin Portable Character Encoding, then the returned strings are in the Host Portable Character Encoding. Otherwise, the result is implementation-dependent. It returns a nonzero status on success; otherwise, it returns a zero status. To free res_name and res_class when finished with the strings, use XFree on each individually.

XGetClassHint can generate a BadWindow error.


Set by application programs to allow window and session managers to obtain the application's resources from the resource database.


The XClassHint structure contains:

typedef struct {
        char *res_name;
        char *res_class; } XClassHint;

The res_name member contains the application name, and the res_class member contains the application class. Note that the name set in this property may differ from the name set as WM_NAME. That is, WM_NAME specifies what should be displayed in the title bar and, therefore, can contain temporal information (for example, the name of a file currently in an editor's buffer). On the other hand, the name specified as part of WM_CLASS is the formal name of the application that should be used when retrieving the application's resources from the resource database.


The server failed to allocate the requested resource or server memory.
A value for a Window argument does not name a defined Window.