NAME

       malloc_usable_size - obtain size of block of memory allocated from heap

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <malloc.h>

       size_t malloc_usable_size(void *_Nullable ptr);

DESCRIPTION

       This  function  can be used for diagnostics or statistics about allocations from malloc(3)
       or a related function.

RETURN VALUE

       malloc_usable_size() returns a value no less than the  size  of  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).

       ┌───────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │Interface                                                      │ Attribute     │ Value   │
       ├───────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │malloc_usable_size()                                           │ Thread safety │ MT-Safe │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       GNU.

CAVEATS

       The  value  returned by malloc_usable_size() may be greater than the requested size of the
       allocation  because  of  various  internal  implementation  details,  none  of  which  the
       programmer  should rely on.  This function is intended to only be used for diagnostics and
       statistics; writing to the excess memory without first calling realloc(3)  to  resize  the
       allocation is not supported.  The returned value is only valid at the time of the call.

SEE ALSO

       malloc(3)