Posix specifies that @code{putenv} puts the given string directly in
@code{environ}, but some systems make a copy of it instead (e.g.,
-glibc 2.0, or BSD). And when a copy is made, @code{unsetenv} might
-not free it, causing a memory leak (e.g., FreeBSD 4).
+glibc 2.0, or @acronym{BSD}). And when a copy is made, @code{unsetenv} might
+not free it, causing a memory leak (e.g., Free@acronym{BSD} 4).
On some systems @code{putenv ("FOO")} removes @samp{FOO} from the
environment, but this is not standard usage and it dumps core
@prindex @code{signal}
Normally @code{signal} takes a handler function with a return type of
@code{void}, but some old systems required @code{int} instead. Any
-actual @code{int} value returned is not used, this is only a
+actual @code{int} value returned is not used; this is only a
difference in the function prototype demanded.
-All systems we know of in current use take @code{void}. Presumably
+All systems we know of in current use return @code{void}. The
@code{int} was to support K&R C, where of course @code{void} is not
available. @code{AC_TYPE_SIGNAL} (@pxref{Particular Types}) can be
used to establish the correct type in all cases.
@prindex @code{getpgid}
@prindex @code{getpgrp}
Define @code{GETPGRP_VOID} if it is an error to pass 0 to
-@code{getpgrp}; this is the Posix behavior. On older BSD
+@code{getpgrp}; this is the Posix behavior. On older @acronym{BSD}
systems, you must pass 0 to @code{getpgrp}, as it takes an argument and
behaves like Posix's @code{getpgid}.
@uref{http://www.gnu.org/software/gnulib/, Gnulib}, which aims to
provide a centralized repository of such portability functions (among
other things). The source files are available online, under various
-licences, mostly GNU GPL or GNU LGPL.
+licences, mostly @acronym{GNU} @acronym{GPL} or @acronym{GNU} @acronym{LGPL}.
@defmac AC_LIBOBJ (@var{function})
@acindex{LIBOBJ}
@item @file{sys/mount.h}
@hdrindex{sys/mount.h}
-On FreeBSD 4.8 on ia32 and using gcc version 2.95.4,
+On Free@acronym{BSD} 4.8 on ia32 and using gcc version 2.95.4,
@file{sys/params.h} is a prerequisite.
@item @file{sys/ptem.h}
@hdrindex{string.h}
@hdrindex{float.h}
@hdrindex{ctype.h}
-Define @code{STDC_HEADERS} if the system has @acronym{ANSI} C header files.
+Define @code{STDC_HEADERS} if the system has C header files
+conforming to @acronym{ANSI} C89 (@acronym{ISO} C90).
Specifically, this macro checks for @file{stdlib.h}, @file{stdarg.h},
@file{string.h}, and @file{float.h}; if the system has those, it
-probably has the rest of the @acronym{ANSI} C header files. This macro also
+probably has the rest of the C89 header files. This macro also
checks whether @file{string.h} declares @code{memchr} (and thus
presumably the other @code{mem} functions), whether @file{stdlib.h}
declare @code{free} (and thus presumably @code{malloc} and other related
functions), and whether the @file{ctype.h} macros work on characters
-with the high bit set, as @acronym{ANSI} C requires.
+with the high bit set, as the C standard requires.
-Use @code{STDC_HEADERS} instead of @code{__STDC__} to determine whether
-the system has @acronym{ANSI}-compliant header files (and probably C library
-functions) because many systems that have GCC do not have @acronym{ANSI} C
-header files.
+Nowadays this macro is becoming obsolete. However, if you use it, your
+code can refer to @code{STDC_HEADERS} instead of @code{__STDC__} to
+determine whether the system has conforming header files (and probably C
+library functions). This is useful if you worry about portability
+to ancient systems that lack C89 header files.
@hdrindex{string.h}
@hdrindex{strings.h}
-On systems without @acronym{ANSI} C headers, there is so much variation
+Nowadays @file{string.h} is part of the C standard and declares functions like
+@code{strcpy}, and @file{strings.h} is standardized by Posix and declares
+@acronym{BSD} functions like @code{bcopy}; but
+historically, string functions were a major sticking point in this area.
+If you worry about portability to ancient systems without standard
+headers, there is so much variation
that it is probably easier to declare the functions you use than to
-figure out exactly what the system header files declare. Some systems
-contain a mix of functions from @acronym{ANSI} and @acronym{BSD}; some are
-mostly @acronym{ANSI} but lack @samp{memmove}; some define the
+figure out exactly what the system header files declare. Some ancient systems
+contain a mix of functions from the C standard and from @acronym{BSD}; some are
+mostly standard but lack @samp{memmove}; some define the
@acronym{BSD} functions as macros in @file{string.h} or
@file{strings.h}; some have only the @acronym{BSD} functions but
@file{string.h}; some declare the memory functions in @file{memory.h},
some in @file{string.h}; etc. It is probably sufficient to check for
one string function and one memory function; if the library has the
-@acronym{ANSI} versions of those then it probably has most of the others.
+standard versions of those then it probably has most of the others.
If you put the following in @file{configure.ac}:
@example
this:
@example
-AC_PROG_CC([cl egcs gcc cc])
+AC_PROG_CC([gcc cl cc])
@end example
-If the C compiler is not in @acronym{ANSI} mode by default, try to add an
-option to output variable @code{CC} to make it so. This macro tries
-various options that select @acronym{ANSI} C on some system or another. It
-considers the compiler to be in @acronym{ANSI} mode if it handles function
-prototypes correctly.
+If the C compiler does not handle function prototypes correctly by
+default, try to add an option to output variable @code{CC} to make it
+so. This macro tries various options that select standard-conformance
+modes on various systems.
After calling this macro you can check whether the C compiler has been
-set to accept @acronym{ANSI} C; if not, the shell variable
-@code{ac_cv_prog_cc_c89} is set to @samp{no}. If you wrote your source
-code in @acronym{ANSI} C, you can make an un-@acronym{ANSI}fied copy of it by
-using the program @code{ansi2knr}, which comes with Automake. See also
-under @code{AC_C_PROTOTYPES} below.
+set to accept @acronym{ANSI} C89 (@acronym{ISO} C90); if not, the shell
+variable
+@code{ac_cv_prog_cc_c89} is set to @samp{no}. See also
+@code{AC_C_PROTOTYPES} below.
If using the @acronym{GNU} C compiler, set shell variable @code{GCC} to
@samp{yes}. If output variable @code{CFLAGS} was not already set, set
@defmac AC_C_CONST
@acindex{C_CONST}
@cvindex const
-If the C compiler does not fully support the @acronym{ANSI} C qualifier
-@code{const}, define @code{const} to be empty. Some C compilers that do
+If the C compiler does not fully support the @code{const} keyword,
+define @code{const} to be empty. Some C compilers that do
not define @code{__STDC__} do support @code{const}; some compilers that
define @code{__STDC__} do not completely support @code{const}. Programs
can simply use @code{const} as if every C compiler supported it; for
@code{volatile}, you are at its mercy anyway. At least your
program will compile, when it wouldn't before.
-In general, the @code{volatile} keyword is a feature of @acronym{ANSI} C, so
+In general, the @code{volatile} keyword is a standard C feature, so
you might expect that @code{volatile} is available only when
@code{__STDC__} is defined. However, Ultrix 4.3's native compiler does
support volatile, but does not define @code{__STDC__}.
@cvindex PARAMS
If function prototypes are understood by the compiler (as determined by
@code{AC_PROG_CC}), define @code{PROTOTYPES} and @code{__PROTOTYPES}.
-In the case the compiler does not handle
-prototypes, you should use @code{ansi2knr}, which comes with the
-Automake distribution, to unprotoize function definitions. For
-function prototypes, you should first define @code{PARAMS}:
-
-@example
-#ifndef PARAMS
-# if PROTOTYPES
-# define PARAMS(protos) protos
-# else /* no PROTOTYPES */
-# define PARAMS(protos) ()
-# endif /* no PROTOTYPES */
-#endif
-@end example
-
-@noindent
-then use it this way:
-
-@example
-size_t my_strlen PARAMS ((const char *));
-@end example
-@end defmac
-
-This macro also defines @code{__PROTOTYPES}; this is for the benefit of
+Defining @code{__PROTOTYPES} is for the benefit of
header files that cannot use macros that infringe on user name space.
+@end defmac
@defmac AC_PROG_GCC_TRADITIONAL
@acindex{PROG_GCC_TRADITIONAL}
@option{-traditional}. That usually happens when the fixed header files
have not been installed on an old system. Since recent versions of the
@acronym{GNU} C compiler fix the header files automatically when installed,
-this is becoming a less prevalent problem.
+this macro is becoming obsolete.
@end defmac
like this:
@example
-AC_PROG_CXX([cl KCC CC cxx cc++ xlC aCC c++ g++ egcs gcc])
+AC_PROG_CXX([gcc cl KCC CC cxx cc++ xlC aCC c++ g++])
@end example
If using the @acronym{GNU} C++ compiler, set shell variable @code{GXX} to
compilers to search for, just as in @code{AC_PROG_F77}.
If the output variable @code{FCFLAGS} was not already set in the
-environment, then set it to @option{-g -02} for GNU @code{g77} (or
+environment, then set it to @option{-g -02} for @acronym{GNU} @code{g77} (or
@option{-O2} where @code{g77} does not accept @option{-g}). Otherwise,
set @code{FCFLAGS} to @option{-g} for all other Fortran compilers.
@end defmac
@defmac AC_AIX
@acindex{AIX}
@cvindex _ALL_SOURCE
-If on @acronym{AIX}, define @code{_ALL_SOURCE}. Allows the use of some @acronym{BSD}
+If on @acronym{AIX}, define @code{_ALL_SOURCE}.
+Allows the use of some @acronym{BSD}
functions. Should be called before any macros that run the C compiler.
@end defmac
Test programs can use @code{#if} or @code{#ifdef} to check the values of
preprocessor macros defined by tests that have already run. For
-example, if you call @code{AC_HEADER_STDC}, then later on in
-@file{configure.ac} you can have a test program that includes an
-@acronym{ANSI} C header file conditionally:
+example, if you call @code{AC_HEADER_STDBOOL}, then later on in
+@file{configure.ac} you can have a test program that includes
+@file{stdbool.h} conditionally:
@example
@group
-#if STDC_HEADERS
-# include <stdlib.h>
+#if HAVE_STDBOOL_H
+# include <stdbool.h>
#endif
@end group
@end example
@node Test Functions
@subsection Test Functions
-Function declarations in test programs should have a prototype
-conditionalized for C++. In practice, though, test programs rarely need
-functions that take arguments.
-
-@example
-#ifdef __cplusplus
-foo (int i)
-#else
-foo (i) int i;
-#endif
-@end example
+These days it's safe to assume support for function prototypes
+(introduced in C89).
Functions that test programs declare should also be conditionalized for
C++, which requires @samp{extern "C"} prototypes. Make sure to not
@example
#ifdef __cplusplus
-extern "C" void *malloc (size_t);
-#else
-void *malloc ();
+extern "C"
#endif
+void *valloc (size_t);
@end example
If a test program calls a function with invalid parameters (just to see
A public-domain clone of the Korn shell called @command{pdksh} is widely
available: it has most of the @samp{ksh88} features along with a few of
its own. It will usually set @code{KSH_VERSION}, except if invoked as
-@command{/bin/sh} on OpenBSD, and similarly to Bash you can require
+@command{/bin/sh} on Open@acronym{BSD}, and similarly to Bash you can require
Posix compatibility by running @samp{set -o posix}. Unfortunately, with
@command{pdksh} 5.2.14 (the latest stable version as of February 2006)
Posix mode is buggy and causes @command{pdksh} to depart from Posix in
@item $@{10@}
@cindex positional parameters
The 10th, 11th, @dots{} positional parameters can be accessed only after
-a @code{shift}. The 7th edition shell reported an error if given @code{$@{10@}};
+a @code{shift}. The 7th Edition shell reported an error if given
+@code{$@{10@}}, and
Solaris 10 @command{/bin/sh} still acts that way:
@example
@item @command{eval}
@c -----------------
@prindex @command{eval}
-In some shell implementations (e.g., older @command{ash}, OpenBSD 3.8
+In some shell implementations (e.g., older @command{ash}, Open@acronym{BSD} 3.8
@command{sh}, @command{pdksh} v5.2.14 99/07/13.2, and @command{zsh}
4.2.5), the arguments of @samp{eval} are evaluated in a context where
@samp{$?} is 0, so they exhibit behavior like this:
A format string starting with a @samp{-} can cause problems.
Bash (e.g., 2.05b) will interpret it as an options string and
give an error. And @samp{--} to mark the end of options is not good
-in the NetBSD Almquist shell (e.g., 0.4.6) which will take that
+in the Net@acronym{BSD} Almquist shell (e.g., 0.4.6) which will take that
literally as the format string. Putting the @samp{-} in a @samp{%c}
or @samp{%s} is probably the easiest way to avoid doubt,
are equivalent, but on Solaris hosts (for example) @command{cp -r}
reads from pipes instead of replicating them.
-Some @command{cp} implementations (e.g., BSD/OS 4.2) do not allow
+Some @command{cp} implementations (e.g., @acronym{BSD/OS} 4.2) do not allow
trailing slashes at the end of nonexistent destination directories. To
avoid this problem, omit the trailing slashes. For example, use
@samp{cp -R source /tmp/newdir} rather than @samp{cp -R source
the system calls that @command{cp} uses; traditionally this was
@code{utime}, which has 1-second resolution, but some newer
@command{cp} implementations use @code{utimes}, which has
-1-microsecond resolution. These newer implementations include GNU
-coreutils 5.0.91 or later, and Solaris 8 (sparc) patch 109933-02 or
+1-microsecond resolution. These newer implementations include @acronym{GNU}
+Core Utilities 5.0.91 or later, and Solaris 8 (sparc) patch 109933-02 or
later. Unfortunately as of January 2006 there is still no system
call to set time stamps to the full nanosecond resolution.
it does not happen. It is not something @command{cp} itself has control
over.
-In SysV any user can chown files to any other user, and SysV also had a
-non-sticky @file{/tmp}. That undoubtedly derives from the heritage of
-SysV in a business environment without hostile users. BSD changed this
+In Unix System V any user can chown files to any other user, and System
+V also has a non-sticky @file{/tmp}. That probably derives from the
+heritage of System V in a business environment without hostile users.
+@acronym{BSD} changed this
to be a more secure model where only root can @command{chown} files and
a sticky @file{/tmp} is used. That undoubtedly derives from the heritage
-of BSD in a campus environment.
+of @acronym{BSD} in a campus environment.
-Linux by default follows BSD, but it can be configured to allow
-@command{chown}. HP-UX as an alternate example follows SysV, but it can
+@acronym{GNU}/Linux and Solaris by default follow @acronym{BSD}, but
+can be configured to allow a System V style @command{chown}. On the
+other hand, @acronym{HP-UX} follows System V, but can
be configured to use the modern security model and disallow
-@command{chown}. Since it is an administrator configurable parameter
+@command{chown}. Since it is an administrator-configurable parameter
you can't use the name of the kernel as an indicator of the behavior.
Posix does not clearly specify whether @samp{mkdir -p foo}
should succeed when @file{foo} is a symbolic link to an already-existing
-directory. GNU Coreutils 5.1.0 @command{mkdir} succeeds, but Solaris
-@command{mkdir} fails.
+directory. The @acronym{GNU} Core Utilities 5.1.0 @command{mkdir}
+succeeds, but Solaris @command{mkdir} fails.
Not all @code{mkdir -p} implementations are thread-safe. When it is not
and you call @code{mkdir -p a/b} and @code{mkdir -p a/c} at the same
time, both will detect that @file{a/} is missing, one will create
@file{a/}, then the other will try to create @file{a/} and die with a
-@code{File exists} error. At least Solaris 10, NetBSD 1.6, and OpenBSD
-3.4 have an unsafe @code{mkdir -p}. GNU Coreutils (since Fileutils
-version 4.0c), FreeBSD 5.0, and NetBSD-current are known to have a
+@code{File exists} error. At least Solaris 10, Net@acronym{BSD} 1.6, and Open@acronym{BSD}
+3.4 have an unsafe @code{mkdir -p}. The @acronym{GNU} Core Utilities
+(since @samp{fileutils}
+version 4.0c), Free@acronym{BSD} 5.0, and Net@acronym{BSD}-current are
+known to have a
race-free @code{mkdir -p}. This possible race is harmful in parallel
builds when several @file{Makefile} rules call @code{mkdir -p} to
construct directories. You may use @command{mkinstalldirs} or
Posix says that the @samp{$<} construct in makefiles can be
used only in inference rules and in the @samp{.DEFAULT} rule; its
meaning in ordinary rules is unspecified. Solaris @command{make}
-for instance will replace it with the empty string. OpenBSD (3.0 and
+for instance will replace it with the empty string. Open@acronym{BSD} (3.0 and
later) @command{make} will diagnose these uses and error out.
@item Command execution
Since 1992 Posix has required that @command{make} must invoke
each command with the equivalent of a @samp{sh -c} subshell. However,
-many @command{make} implementations, including BSD make through 2004,
+many @command{make} implementations, including @acronym{BSD} make through 2004,
use @samp{sh -e -c} instead, and the @option{-e} option causes the
subshell to exit immediately if a subsidiary simple-command fails. For
example, the command @samp{touch T; rm -f U} will always attempt to
This syntax (@code{foo=bar make -e}) is portable only when used
outside of a @file{Makefile}, for instance from a script or from the
-command line. When run inside a @command{make} rule, GNU
+command line. When run inside a @command{make} rule, @acronym{GNU}
@command{make} 3.80 and prior versions forget to propagate the
@code{-e} option to sub-@command{make}s.
Do not force @code{SHELL = /bin/sh} because that is not correct
everywhere. For instance @acronym{DJGPP} lacks @code{/bin/sh}, and when
-its GNU @code{make} port sees such a setting it enters a special
+its @acronym{GNU} @code{make} port sees such a setting it enters a special
emulation mode where features like pipes and redirections are emulated
on top of DOS's @command{command.com}. Unfortunately this emulation is
incomplete; for instance it does not handle command substitutions.
@item The @file{obj/} subdirectory.
@cindex @file{obj/}, subdirectory
-@cindex BSD @command{make} and @file{obj/}
+@cindex @acronym{BSD} @command{make} and @file{obj/}
Never name one of your subdirectories @file{obj/} if you don't like
surprises.
-If an @file{obj/} directory exists, BSD @command{make} will enter it
+If an @file{obj/} directory exists, @acronym{BSD} @command{make} will enter it
before reading @file{Makefile}. Hence the @file{Makefile} in the
current directory will not be read.
If a target does not need to be rebuilt, @acronym{GNU} @command{make} uses the
file name found during the @code{VPATH} search.
-Other @command{make} implementations, like NetBSD @command{make}, are
+Other @command{make} implementations, like Net@acronym{BSD} @command{make}, are
easier to describe: the file name found during the @code{VPATH} search
will be used whether the target needs to be rebuilt or not. Therefore
new files are created locally, but existing files are updated at their
@code{VPATH} location.
-OpenBSD and FreeBSD @command{make}s, however, will never perform a
+Open@acronym{BSD} and Free@acronym{BSD} @command{make}s, however, will
+never perform a
@code{VPATH} search for a dependency which has an explicit rule.
This is extremely annoying.
(e.g., @code{mkdir build && cd build && ../configure}), this means the
@acronym{GNU}
@command{make} will build everything locally in the @file{build}
-directory, while BSD @command{make} will build new files locally and
+directory, while @acronym{BSD} @command{make} will build new files locally and
update existing files in the source directory.
@example
Building bar.x
@end example
-Note how NetBSD @command{make} updates @file{../bar.x} in its VPATH
-location, and how FreeBSD, OpenBSD, and Tru64 @command{make} always
+Note how Net@acronym{BSD} @command{make} updates @file{../bar.x} in its
+VPATH location, and how Free@acronym{BSD}, Open@acronym{BSD}, and Tru64
+@command{make} always
update @file{bar.x}, even when @file{../bar.x} is up to date.
Another point worth mentioning is that once @acronym{GNU} @command{make} has
rule, @acronym{GNU} @command{make} will magically start to work: it
knows that @code{bar.x} hasn't been updated, therefore it doesn't
discard the result from @code{VPATH} (@file{../bar.x}) in succeeding
-uses. Tru64 will also work, but FreeBSD and OpenBSD still don't.
+uses. Tru64 will also work, but Free@acronym{BSD} and Open@acronym{BSD}
+still don't.
@example
% @kbd{cat Makefile}
@sp 1
-@ovindex U
-@cindex @code{$U}
-When asked for automatic de-ANSI-fication, Automake needs
-@code{LIBOBJS}'ed file names to have @samp{$U} appended to the base
-names. Libtool requires the definition of @code{LTLIBOBJS}, whose
-suffixes are mapped to @samp{.lo}. People used to run snippets such as:
-
-@example
-# This is necessary so that .o files in LIBOBJS are also built via
-# the ANSI2KNR-filtering rules.
-LIBOBJS=`echo "$LIBOBJS" | sed 's/\.o /\$U.o /g;s/\.o$/\$U.o/'`
-LTLIBOBJS=`echo "$LIBOBJS" | sed 's/\.o/\.lo/g'`
-AC_SUBST([LTLIBOBJS])
-@end example
-
-@noindent
-Note that this code is @emph{wrong}, because @samp{.o} is not the only
-possible extension@footnote{
-@c
-Yet another reason why assigning @code{LIBOBJS} directly is discouraged.
-@c
-}! It should have read:
-
-@example
-# This is necessary so that .o files in LIBOBJS are also built via
-# the ANSI2KNR-filtering rules.
-LIB@@&t@@OBJS=`echo "$LIB@@&t@@OBJS" |
- sed 's,\.[[^.]]* ,$U&,g;s,\.[[^.]]*$,$U&,'`
-LTLIBOBJS=`echo "$LIB@@&t@@OBJS" |
- sed 's,\.[[^.]]* ,.lo ,g;s,\.[[^.]]*$,.lo,'`
-AC_SUBST([LTLIBOBJS])
-@end example
-
-@sp 1
-
-You no longer have to use this: @code{AC_OUTPUT} normalizes
-@code{LIBOBJS} and @code{LTLIBOBJS} (hence it works with any version of
-Automake and Libtool). Just remove these lines (@command{autoupdate}
-cannot handle this task, since this is not a macro).
-
-Note that @code{U} must not be used in your Makefiles.
-
@ovindex LIBOBJDIR
When used with Automake 1.10 or newer, a suitable value for
@code{LIBOBJDIR} is set so that the @code{LIBOBJS} and @code{LTLIBOBJS}
@group
AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
[[#if !defined _AIX
-# error _AIX not defined
+ error: This isn't AIX!
#endif
]])],
[is_aix=yes],
produces may be distributed or used. In Autoconf version 1, they were
covered by the @acronym{GNU} General Public License. We still encourage
software authors to distribute their work under terms like those of the
-GPL, but doing so is not required to use Autoconf.
+@acronym{GPL}, but doing so is not required to use Autoconf.
Of the other files that might be used with @command{configure},
@file{config.h.in} is under whatever copyright you use for your
@file{configure.ac}. @file{config.sub} and @file{config.guess} have an
-exception to the GPL when they are used with an Autoconf-generated
+exception to the @acronym{GPL} when they are used with an Autoconf-generated
@command{configure} script, which permits you to distribute them under the
same terms as the rest of your package. @file{install-sh} is from the X
Consortium and is not copyrighted.
details. You should be aware that disabling the cache slows down the
Autoconf test suite by 40%. The more @acronym{GNU} Build System
components are used, the more the cache is useful; for instance
-running @samp{autoreconf -f} on the Coreutils is twice slower without
+running @samp{autoreconf -f} on the Core Utilities is twice slower without
the cache @emph{although @option{--force} implies that the cache is
not fully exploited}, and eight times slower than without
@option{--force}.
projects / thirdparty / autoconf.git / commitdiff
