malloc_usable_size (3) - Linux Man Pages
malloc_usable_size: obtain size of block of memory allocated from heap
malloc_usable_size - obtain size of block of memory allocated from heap
DESCRIPTIONThe malloc_usable_size() function returns the number of usable bytes in the block pointed to by ptr, a pointer to a block of memory allocated by malloc(3) or a related function.
RETURN VALUEmalloc_usable_size() returns the number of usable bytes in the block of allocated memory pointed to by ptr. If ptr is NULL, 0 is returned.
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
CONFORMING TOThis function is a GNU extension.
NOTESThe 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.
COLOPHONThis page is part of release 5.05 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.