kc3-lang/gnulib/doc/posix-headers/stdalign.texi

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• Hash : 775dbeeb
  Author :
  Date : 2016-09-06T14:26:05
  

  stdalign: correct mistake in alignof doc
  
  Problem reported by Joseph Myers in:
  https://gcc.gnu.org/ml/gcc-patches/2016-09/msg00340.html
  * doc/posix-headers/stdalign.texi: Do not imply that C11 prohibits
  alignof(S) where S is a structure containing a flexible array
  member.  The Gnulib substitute does not support this, but C11 does.
  

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• doc/posix-headers/stdalign.texi

• @node stdalign.h
  @section @file{stdalign.h}
  
  POSIX specification:@* Not in POSIX yet, but we expect it will be.
  ISO C11 (latest free draft
  @url{http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf})
  sections 6.5.3.4, 6.7.5, 7.15.
  C++11 (latest free draft
  @url{http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf})
  section 18.10.
  
  Gnulib module: stdalign
  
  Portability problems fixed by Gnulib:
  @itemize
  @item
  This header file is missing on most circa-2011 platforms.
  @item
  Clang 3.0's @code{<stdalign.h>} does not define @code{alignof}/@code{_Alignof}.
  @item
  The @code{alignof} and @code{_Alignof} macros return too large values for
  the types @code{double} and @code{long long} in GCC 4.7.0.
  @end itemize
  
  Portability problems not fixed by Gnulib:
  @itemize
  @item
  In ISO C11, the operand of @code{alignof}/@code{_Alignof} must be a
  parenthesized type.  Recent versions of GCC support an extension in
  which the operand can also be a unary expression, as with
  @code{sizeof}.  The Gnulib substitute does not support this extension.
  @item
  On most pre-C11 platforms, the operand of
  @code{alignof}/@code{_Alignof} cannot be a structure type containing a
  flexible array member.
  @item
  @code{_Alignas} and @code{alignas} are not always supported;
  on platforms lacking support, the
  macro @code{__alignas_is_defined} is not defined.
  Supported compilers include GCC, IBM C, Sun C 5.9 and later,
  and MSVC 7.0 and later.
  @item
  Some compilers do not support alignment via
  @code{alignas}/@code{_Alignas} of @code{auto} variables (i.e.,
  variables on the stack).  They diagnose and ignore the alignment: Sun
  C 5.11.
  @item
  Some linkers do not support operands of @code{_Alignas}/@code{alignas}
  that are greater than 8: mingw.
  @item
  Some compilers require the operand of @code{_Alignas}/@code{alignas}
  to be a single integer constant, not an expression: MSVC 7.0 through
  at least 10.0.
  @item
  The Sun C 5.11 compiler sometimes mishandles the alignment of multiple
  external variables that are declared close together with
  @code{_Alignas}/@code{alignas}.  This compiler bug causes the Gnulib
  module @code{stdalign-tests} to fail.  The Sun Studio Developer Bug
  Report Review Team assigned the internal review ID 2125432 (dated
  2011-11-01) to this issue.
  @item
  @code{<stdalign.h>} must be #included before @code{_Alignas} and
  @code{_Alignof} can be used.
  @item
  You cannot assume that @code{_Alignas} and @code{_Alignof} are reserved words;
  they might be macros.
  @end itemize
  

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