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For many years Gnulib has targeted C89 and has resisted using C99 features, as some Gnulib-using programs still wanted to target C89. As this no longer seems to be the case, relax the porting requirements to allow some C99 features. This is merely a change to the documentation, to give other Gnulib developers a chance to weigh in on the topic. * doc/extern-inline.texi (extern inline): * doc/gnulib-readme.texi (Portability guidelines): * doc/gnulib-tool.texi (Initial import): * doc/gnulib.texi (Header files): Modernize to talk about C99 and C11 instead of C89 and C99. * doc/gnulib-readme.texi (Portability guidelines): Now a section, not merely a subsection, so that it can be split up. Modernize a bit. (C language versions, C99 features assumed) (C99 features avoided): New sections.
101 lines
3.4 KiB
Plaintext
101 lines
3.4 KiB
Plaintext
@c GNU extern-inline module documentation
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@c Copyright (C) 2013-2017 Free Software Foundation, Inc.
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@c Permission is granted to copy, distribute and/or modify this document
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@c under the terms of the GNU Free Documentation License, Version 1.3
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@c or any later version published by the Free Software Foundation;
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@c with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
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@c Texts. A copy of the license is included in the ``GNU Free
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@c Documentation License'' file as part of this distribution.
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@c Written by Paul Eggert.
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@node extern inline
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@section Extern inline functions
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@cindex extern inline
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@cindex inline
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The @code{extern-inline} module supports the use of C99-style
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@code{extern inline} functions so that the code still runs on
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compilers that do not support this feature correctly.
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C code ordinarily should not use @code{inline}. Typically it is
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better to let the compiler figure out whether to inline, as compilers
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are pretty good about optimization nowadays. In this sense,
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@code{inline} is like @code{register}, another keyword that is
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typically no longer needed.
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Functions defined (not merely declared) in headers are an exception,
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as avoiding @code{inline} would commonly cause problems for these
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functions. Suppose @file{aaa.h} defines the function @code{aaa_fun},
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and @file{aaa.c}, @file{bbb.c} and @file{ccc.c} all include
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@file{aaa.h}. If code is intended to portable to non-C99 compilers,
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@code{aaa_fun} cannot be declared with the C99 @code{inline} keyword.
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This problem cannot be worked around by making @code{aaa_fun} an
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ordinary function, as it would be defined three times with external
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linkage and the definitions would clash. Although @code{aaa_fun}
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could be a static function, with separate compilation if
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@code{aaa_fun} is not inlined its code will appear in the executable
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three times.
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To avoid this code bloat, @file{aaa.h} can do this:
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@example
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/* aaa.h */
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/* #include any other headers here */
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#ifndef _GL_INLINE_HEADER_BEGIN
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#error "Please include config.h first."
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#endif
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_GL_INLINE_HEADER_BEGIN
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#ifndef AAA_INLINE
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# define AAA_INLINE _GL_INLINE
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#endif
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...
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AAA_INLINE int
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aaa_fun (int i)
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@{
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return i + 1;
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@}
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...
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_GL_INLINE_HEADER_END
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@end example
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@noindent
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and @file{aaa.c} can do this:
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@example
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/* aaa.c */
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#include <config.h>
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#define AAA_INLINE _GL_EXTERN_INLINE
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#include <aaa.h>
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@end example
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@noindent
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whereas @file{bbb.c} and @file{ccc.c} can include @file{aaa.h} in the
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usual way. C99 compilers expand @code{AAA_INLINE} to C99-style
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@code{inline} usage, where @code{aaa_fun} is declared @code{extern
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inline} in @file{aaa.c} and plain @code{inline} in other modules.
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Non-C99 compilers that are compatible with GCC use GCC-specific syntax
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to accomplish the same ends. Other non-C99 compilers use @code{static
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inline} so they suffer from code bloat, but they are not mainline
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platforms and will die out eventually.
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@findex _GL_INLINE
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@code{_GL_INLINE} is a portable alternative to C99 plain @code{inline}.
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@findex _GL_EXTERN_INLINE
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@code{_GL_EXTERN_INLINE} is a portable alternative to C99 @code{extern inline}.
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@findex _GL_INLINE_HEADER_BEGIN
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Invoke @code{_GL_INLINE_HEADER_BEGIN} before all uses of
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@code{_GL_INLINE} in an include file. This suppresses some
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bogus warnings in GCC versions before 5.1. If an include file includes
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other files, it is better to invoke this macro after including the
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other files.
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@findex _GL_INLINE_HEADER_END
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Invoke @code{_GL_INLINE_HEADER_END} after all uses of
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@code{_GL_INLINE} in an include file.
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