MALLOC_USABLE_SIZE(3)     (2017-09-15)      MALLOC_USABLE_SIZE(3)

     NAME
          malloc_usable_size - obtain size of block of memory
          allocated from heap

     SYNOPSIS
          #include <malloc.h>

          size_t malloc_usable_size (void *ptr);

     DESCRIPTION
          The 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 func-
          tion.

     RETURN VALUE
          malloc_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.

     ATTRIBUTES
          For an explanation of the terms used in this section, see
          attributes(7).  allbox; lbw20 lb lb l l l.
          Interface Attribute Value T{ malloc_usable_size()
          T}   Thread safety  MT-Safe

     CONFORMING TO
          This function is a GNU extension.

     NOTES
          The value returned by malloc_usable_size() may be greater
          than the requested size of the allocation because of align-
          ment 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 intro-
          spection.

     SEE ALSO
          malloc(3)

     COLOPHON
          This page is part of release 5.10 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/.

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