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NAME | SYNOPSIS | DESCRIPTION | VERSIONS | STANDARDS | HISTORY | SEE ALSO |
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void(3type) void(3type)
void - abstract type
void *
A pointer to any object type may be converted to a pointer to
void and back. POSIX further requires that any pointer,
including pointers to functions, may be converted to a pointer to
void and back.
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 void * value to a type incompatible to
that of the underlying data, because that would result in
undefined behavior.
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 void.
A value of this type can't be dereferenced, as it would give a
value of type 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 void or of a function as
1. A consequence of this is that sizeof is also allowed on void
and on function types, and returns 1.
Use with printf(3) and scanf(3)
The conversion specifier for void * for the printf(3) and the
scanf(3) families of functions is p.
The POSIX requirement about compatibility between void * and
function pointers was added in POSIX.1-2008 Technical Corrigendum
1 (2013).
C11, POSIX.1-2008.
C89, POSIX.1-2001.
malloc(3), memcmp(3), memcpy(3), memset(3), intptr_t(3type)
Linux man-pages (unreleased) (date) void(3type)
Pages that refer to this page: NULL(3const)
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HTML rendering created 2023-12-22 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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