XFree - free client data
XFree(data) void *data;
data Specifies the data that is to be freed.
The XFree function is a general-purpose Xlib routine that frees the specified data. You must use it to free any objects that were allocated by Xlib, unless an alternate function is explicitly specified for the object. A NULL pointer cannot be passed to this function.
Xlib - C Language X Interface X Version 11 Release 6.4 1