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 *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 function.

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).

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

STANDARDS

       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 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.

SEE ALSO

       malloc(3)