'\" t
.\" Copyright (c) 2012 by Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH malloc_usable_size 3 2023-07-20 "Linux man-pages 6.05.01"
.SH NAME
malloc_usable_size \- obtain size of block of memory allocated from heap
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <malloc.h>
.PP
.BI "size_t malloc_usable_size(void *_Nullable " ptr );
.fi
.SH DESCRIPTION
This function can be used for
diagnostics or statistics about allocations from
.BR malloc (3)
or a related function.
.SH RETURN VALUE
.BR malloc_usable_size ()
returns a value no less than
the size of the block of allocated memory pointed to by
.IR ptr .
If
.I ptr
is NULL, 0 is returned.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR malloc_usable_size ()
T}	Thread safety	MT-Safe
.TE
.sp 1
.SH STANDARDS
GNU.
.SH CAVEATS
The value returned by
.BR 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
.BR realloc (3)
to resize the allocation is not supported.
The returned value is only valid at the time of the call.
.SH SEE ALSO
.BR malloc (3)