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 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

       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)