The XtCalloc function allocates space for the specified number of array elements of the specified size and initializes the space to zero. If there is insufficient memory to allocate the new block, XtCalloc calls XtErrorMsg.
The XtRealloc function changes the size of a block of storage (possibly moving it). Then, it copies the old contents (or as much as will fit) into the new block and frees the old block. If there is insufficient memory to allocate the new block, XtRealloc calls XtErrorMsg. If ptr is NULL, XtRealloc allocates the new storage without copying the old contents; that is, it simply calls XtMalloc.
The XtFree function returns storage and allows it to be reused. If ptr is NULL, XtFree returns immediately.
XtNew returns a pointer to the allocated storage. If there is insufficient memory to allocate the new block, XtNew calls XtErrorMsg. XtNew is a convenience macro that calls XtMalloc with the following arguments specified:
((type *) XtMalloc((unsigned) sizeof(type))
XtNewString returns a pointer to the allocated storage. If there is insufficient memory to allocate the new block, XtNewString calls XtErrorMsg. XtNewString is a convenience macro that calls XtMalloc with the following arguments specified:
(strcpy(XtMalloc((unsigned) strlen(str) + 1), str))