malloc_usable_size — obtain size of block of memory allocated from heap
function returns the number of usable bytes in the block
pointed to by
pointer to a block of memory allocated by malloc(3) or a related
the number of usable bytes in the block of allocated memory
pointed to by
ptr is NULL, 0 is
For an explanation of the terms used in this section, see attributes(7).
The value returned by
malloc_usable_size() may be greater than
the requested size of the allocation because of alignment and
minimum size constraints. Although the excess bytes can be
overwritten by the application without ill effects, this is
not good programming practice: the number of excess bytes in
an allocation depends on the underlying implementation.
The main use of this function is for debugging and introspection.
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