void(3type) - Linux manual page (original) (raw)

void(3type) void(3type)

NAME top

   void - abstract type

SYNOPSIS top

   **void ***

DESCRIPTION top

   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.

VERSIONS top

   The POSIX requirement about compatibility between _void *_ and
   function pointers was added in POSIX.1-2008 Technical Corrigendum
   1 (2013).

STANDARDS top

   C11, POSIX.1-2008.

HISTORY top

   C89, POSIX.1-2001.

SEE ALSO top

   [malloc(3)](../man3/malloc.3.html), [memcmp(3)](../man3/memcmp.3.html), [memcpy(3)](../man3/memcpy.3.html), [memset(3)](../man3/memset.3.html), [intptr_t(3type)](../man3/intptr%5Ft.3type.html)

COLOPHON top

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Linux man-pages 6.10 2024-05-02 void(3type)

Pages that refer to this page:NULL(3const)