Note that you should not use auto-increment or auto-decrement
within the first argument to
can be implemented as a macro that dereferences the first argument twice.
function allocates enough storage to hold the combined
structures and copies them into it.
Note that it does not check for duplicate entries.
When it is no longer needed,
free the returned storage by using
X Toolkit Intrinsics - C Language Interface Xlib - C Language X Interface