void(3type) void(3type)
NAME
void - abstract type
SYNOPSIS
void *
DESCRIPTION
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 mecha-
nism 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 al-
lowed 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
The POSIX requirement about compatibility between void * and function
pointers was added in POSIX.1-2008 Technical Corrigendum 1 (2013).
STANDARDS
C11, POSIX.1-2008.
HISTORY
C89, POSIX.1-2001.
SEE ALSO
malloc(3), memcmp(3), memcpy(3), memset(3), intptr_t(3type)
Linux man-pages 6.9.1 2024-05-02 void(3type)
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