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40 lines
1.0 KiB
Plaintext
40 lines
1.0 KiB
Plaintext
@node va_arg
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@section @code{va_arg}
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@findex va_arg
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POSIX specification:@* @url{http://www.opengroup.org/onlinepubs/9699919799/functions/va_arg.html}
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Gnulib module: ---
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Portability problems fixed by Gnulib:
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@itemize
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@end itemize
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Portability problems not fixed by Gnulib:
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@itemize
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@item
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The second argument of @code{va_arg} must be a type that is invariant under
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the ``default argument promotions'' (ISO C 99 6.5.2.2 paragraph 6). This
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means that the following are not valid here:
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@table @asis
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@item @samp{float}
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Use @samp{double} instead.
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@item @samp{bool}
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Use @samp{int} instead.
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@item Integer types smaller than @samp{int}.
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Use @samp{int} or @samp{unsigned int} instead.
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@end table
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This is a portability problem because you don't know the width of some
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abstract types like @code{uid_t}, @code{gid_t}, @code{mode_t}. So, instead of
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@smallexample
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mode = va_arg (ap, mode_t);
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@end smallexample
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you have to write
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@smallexample
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mode = (sizeof (mode_t) < sizeof (int)
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? va_arg (ap, int)
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: va_arg (ap, mode_t));
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@end smallexample
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@end itemize
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