set to accept Standard C; if not, the shell variable
@code{ac_cv_prog_cc_stdc} is set to @samp{no}.
+When attempting to add compiler options, prefer extended functionality
+modes over strict conformance modes. Test for C11 support by checking
+for @code{_Alignas}, @code{_Alignof}, @code{_Noreturn},
+@code{_Static_assert}, UTF-8 string literals, duplicate @code{typedef}s,
+and anonymous structures and unions. Test for C99 support by checking
+for @code{_Bool}, @code{//} comments, flexible array members,
+@code{inline}, signed and unsigned @code{long long int}, mixed code and
+declarations, named initialization of structs, @code{restrict},
+@code{va_copy}, varargs macros, variable declarations in @code{for}
+loops, and variable length arrays. Test for C89 support by checking for
+function prototypes.
+
If using the GNU C compiler, set shell variable @code{GCC} to
@samp{yes}. If output variable @code{CFLAGS} was not already set, set
it to @option{-g -O2} for the GNU C compiler (@option{-O2} on systems
@code{AC_COMPILE_IFELSE} (@pxref{Running the Compiler}) or
@code{AC_RUN_IFELSE} (@pxref{Runtime}).
-@defmac AC_PROG_CC_C89
-@acindex{PROG_CC_C89}
-@caindex prog_cc_c89
-If the C compiler is not in ANSI C89 (ISO C90) mode by
-default, try to add an option to output variable @code{CC} to make it
-so. This macro tries various options that select ANSI C89 on
-some system or another, preferring extended functionality modes over
-strict conformance modes. It considers the compiler to be in
-ANSI C89 mode if it handles function prototypes correctly.
-
-After calling this macro you can check whether the C compiler has been
-set to accept ANSI C89; if not, the shell variable
-@code{ac_cv_prog_cc_c89} is set to @samp{no}.
-
-This macro is rarely needed. It should be used only if your application
-requires C89 and will not work in later C versions. Typical applications
-should use @code{AC_PROG_CC} instead.
-@end defmac
-
-@defmac AC_PROG_CC_C99
-@acindex{PROG_CC_C99}
-@caindex prog_cc_c99
-If the C compiler is not in C99 mode by default, try to add an
-option to output variable @code{CC} to make it so. This macro tries
-various options that select C99 on some system or another, preferring
-extended functionality modes over strict conformance modes. It
-considers the compiler to be in C99 mode if it handles @code{_Bool},
-@code{//} comments, flexible array members, @code{inline}, signed and
-unsigned @code{long long int}, mixed code and declarations, named
-initialization of structs,
-@code{restrict}, @code{va_copy}, varargs macros, variable declarations
-in @code{for} loops, and variable length arrays.
-
-After calling this macro you can check whether the C compiler has been
-set to accept C99; if not, the shell variable
-@code{ac_cv_prog_cc_c99} is set to @samp{no}.
-
-This macro is rarely needed. It should be used only if your application
-requires C99 and will not work in later C versions. Typical applications
-should use @code{AC_PROG_CC} instead.
-
-There is no @code{AC_PROG_CC_C11} macro, as no need for one has been
-identified.
-@end defmac
-
@defmac AC_C_BACKSLASH_A
@acindex{C_BACKSLASH_A}
@cvindex HAVE_C_BACKSLASH_A
@end example
@noindent
-results in:
+might result in:
@example
checking for gcc... gcc
-checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
-checking whether we are cross compiling... no
+checking for C compiler default output file name... a.out
checking for suffix of executables...
+checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
-checking for gcc option to accept ISO C89... none needed
-checking how to run the C preprocessor... gcc -E
+checking for gcc option to accept ISO C11... -std=gnu11
+checking how to run the C preprocessor... gcc -std=gnu11 -E
OK
@end example
The C compiler's traditional name is @command{cc}, but other names like
@command{gcc} are common. Posix 1003.1-2001 and 1003.1-2008 specify the
name @command{c99}, but older Posix editions specified
-@command{c89} and anyway these standard names are rarely used in
+@command{c89}, future POSIX standards will likely specify
+@command{c11}, and anyway these standard names are rarely used in
practice. Typically the C compiler is invoked from makefiles that use
@samp{$(CC)}, so the value of the @samp{CC} make variable selects the
compiler name.
Even when accessing objects defined with a volatile type,
the C standard allows only
-extremely limited signal handlers: the behavior is undefined if a signal
+extremely limited signal handlers: in C99 the behavior is undefined if a signal
handler reads any nonlocal object, or writes to any nonlocal object
whose type is not @code{sig_atomic_t volatile}, or calls any standard
-library function other than @code{abort}, @code{signal}, and (if C99 or later)
+library function other than @code{abort}, @code{signal}, and
@code{_Exit}. Hence C compilers need not worry about a signal handler
-disturbing ordinary computation, unless the computation accesses a
-@code{sig_atomic_t volatile} lvalue that is not a local variable.
-(There is an obscure exception for accesses via a pointer to a volatile
-character, since it may point into part of a @code{sig_atomic_t
-volatile} object.) Posix
-adds to the list of library functions callable from a portable signal
-handler, but otherwise is like the C standard in this area.
+disturbing ordinary computation. C11 and Posix allow some additional
+behavior in a portable signal handler, but are still quite restrictive.
Some C implementations allow memory-access optimizations within each
translation unit, such that actual behavior agrees with the behavior
required by the standard only when calling a function in some other
translation unit, and a signal handler acts like it was called from a
-different translation unit. The C standard hints that in these
+different translation unit. The C99 standard hints that in these
implementations, objects referred to by signal handlers ``would require
explicit specification of @code{volatile} storage, as well as other
implementation-defined restrictions.'' But unfortunately even for this
special case these other restrictions are often not documented well.
+This area was significantly changed in C11, and eventually implementations
+will probably head in the C11 direction, but this will take some time.
@xref{Volatiles, , When is a Volatile Object Accessed?, gcc, Using the
GNU Compiler Collection (GCC)}, for some
restrictions imposed by GCC. @xref{Defining Handlers, ,
Replaced by @code{AC_PREFIX_PROGRAM} (@pxref{AC_PREFIX_PROGRAM}).
@end defmac
+@defmac AC_PROG_CC_C89
+@acindex{PROG_CC_C89}
+Now done by @code{AC_PROG_CC} (@pxref{AC_PROG_CC}).
+@end defmac
+
+@defmac AC_PROG_CC_C99
+@acindex{PROG_CC_C99}
+Now done by @code{AC_PROG_CC} (@pxref{AC_PROG_CC}).
+@end defmac
+
@defmac AC_PROG_CC_STDC
@acindex{PROG_CC_STDC}
Now done by @code{AC_PROG_CC} (@pxref{AC_PROG_CC}).
AC_INIT([Example], [1.0], [bug-example@@example.org])
AC_CHECK_HEADERS([pi.h])
$ @kbd{autoconf -Wall}
-$ @kbd{./configure}
+$ @kbd{./configure CPPFLAGS='-I.'}
checking for gcc... gcc
-checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
-checking whether we are cross compiling... no
+checking for C compiler default output file name... a.out
checking for suffix of executables...
+checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
-checking for gcc option to accept ISO C89... none needed
-checking how to run the C preprocessor... gcc -E
-checking for grep that handles long lines and -e... grep
-checking for egrep... grep -E
+checking for gcc option to accept ISO C11... -std=gnu11
+checking how to run the C preprocessor... gcc -std=gnu11 -E
+checking for grep that handles long lines and -e... /usr/bin/grep
+checking for egrep... /usr/bin/grep -E
checking for ANSI C header files... yes
checking for sys/types.h... yes
checking for sys/stat.h... yes
configure: WARNING: pi.h: see the Autoconf documentation
configure: WARNING: pi.h: section "Present But Cannot Be Compiled"
configure: WARNING: pi.h: proceeding with the compiler's result
-configure: WARNING: ## -------------------------------------- ##
+configure: WARNING: ## --------------------------------------- ##
configure: WARNING: ## Report this to bug-example@@example.org ##
-configure: WARNING: ## -------------------------------------- ##
-checking for pi.h... yes
+configure: WARNING: ## --------------------------------------- ##
+checking for pi.h... no
@end smallexample
@noindent
#endif
]])
$ @kbd{autoconf -Wall}
-$ @kbd{./configure}
+$ @kbd{./configure CPPFLAGS='-I.'}
checking for gcc... gcc
-checking for C compiler default output... a.out
checking whether the C compiler works... yes
-checking whether we are cross compiling... no
+checking for C compiler default output file name... a.out
checking for suffix of executables...
+checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
-checking for gcc option to accept ANSI C... none needed
+checking for gcc option to accept ISO C11... -std=gnu11
checking for number.h... yes
checking for pi.h... yes
@end example
projects / thirdparty / autoconf.git / commitdiff
