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.\" Copyright (c) 2020-2022 by Alejandro Colomar <alx@kernel.org>
.\" and Copyright (c) 2020 by Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\"
.TH void 3type (date) "Linux man-pages (unreleased)"
.SH NAME
void \- abstract type
.SH SYNOPSIS
.nf
.B void *
.fi
.SH DESCRIPTION
A pointer to any object type may be converted to a pointer to
.I void
and back.
POSIX further requires that any pointer,
including pointers to functions,
may be converted to a pointer to
.I void
and back.
.P
Conversions from and to any other pointer type are done implicitly,
not requiring casts at all.
Note that this feature prevents any kind of type checking:
the programmer should be careful not to convert a
.I void *
value to a type incompatible to that of the underlying data,
because that would result in undefined behavior.
.P
This type is useful in function parameters and return value
to allow passing values of any type.
The function will typically use some mechanism to know
the real type of the data being passed via a pointer to
.IR void .
.P
A value of this type can't be dereferenced,
as it would give a value of type
.IR void ,
which is not possible.
Likewise, pointer arithmetic is not possible with this type.
However, in GNU C, pointer arithmetic is allowed
as an extension to the standard;
this is done by treating the size of a
.I void
or of a function as 1.
A consequence of this is that
.I sizeof
is also allowed on
.I void
and on function types, and returns 1.
.SS Use with printf(3) and scanf(3)
The conversion specifier for
.I void *
for the
.BR printf (3)
and the
.BR scanf (3)
families of functions is
.BR p .
.SH VERSIONS
The POSIX requirement about compatibility between
.I void *
and function pointers was added in
POSIX.1-2008 Technical Corrigendum 1 (2013).
.SH STANDARDS
C11, POSIX.1-2008.
.SH HISTORY
C89, POSIX.1-2001.
.SH SEE ALSO
.BR malloc (3),
.BR memcmp (3),
.BR memcpy (3),
.BR memset (3),
.BR intptr_t (3type)
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