__UNCONST(3) - NetBSD Manual Pages

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__UNCONST(3)            NetBSD Library Functions Manual           __UNCONST(3)


NAME

     __UNCONST -- compile time cast-away macro


SYNOPSIS

     #include <sys/cdefs.h>

     void
     __UNCONST(x);

     void
     __UNVOLATILE(x);


DESCRIPTION

     The __UNCONST() macro can be used to omit warnings produced by certain
     compilers when operating with pointers declared with the const type qual-
     ifier in a context without such qualifier.  Examples include passing a
     pointer declared with the const qualifier to a function without such
     qualifier, and variable assignment from a const pointer to a non-const
     pointer.  In the same vein, the __UNVOLATILE() macro can be used to
     exclude warnings related to the volatile type qualifier.


IMPLEMENTATION NOTES

     These macros are implemented by explicitly using unsigned long instead of
     intptr_t, a signed type guaranteed to hold a pointer.


SEE ALSO

     cc(1), cdefs(3)


CAVEATS

     As both macros may hide valid errors, their usage is not recommended
     unless there is a well-thought reason for a cast.  A typical use case for
     __UNCONST() involve an API that does not follow the so-called ``const
     correctness'' even if it would be appropriate.  Valid use cases of
     __UNVOLATILE() include passing a volatile pointer to memset(3).

     Use of this macro is non-portable; this is part of the implementation
     namespace and should only be used in NetBSD code.

NetBSD 8.3                     October 17, 2013                     NetBSD 8.3