Can't make automake to use C++11 - c++

Question

I'm working on some project and it seems that I can't make automake script to use C++11.
In rootdir of my project I have file Makefile.am which look like this (it was automade by eclipse):
SUBDIRS=src
Then in /rootdir/src I have Makefile.am that looks like this:
AM_CXXFLAGS=-Wall -fPIC -std=gnu++11 -DVERSION=\"$(VERSION)\" -DPROG="\"$(PACKAGE)\""
bin_PROGRAMS = algatorc
algatorc_SOURCES = algatorc.cpp
include_HEADERS = Timer.hpp TestSetIterator.hpp TestCase.hpp ETestSet.hpp EParameter.hpp Entity.hpp ParameterSet.hpp AbsAlgorithm.hpp Log.hpp JSON.hpp JSONValue.hpp
lib_LIBRARIES = libAlgatorc.a
libAlgatorc_a_SOURCES = ParameterSet.cpp TestCase.cpp EParameter.cpp ETestSet.cpp TestSetIterator.cpp Entity.cpp Timer.cpp JSON.cpp JSONValue.cpp AbsAlgorithm.cpp
algatorc_LDADD=libAlgatorc.a
So, I added -std=gnu++11 for C++11 support but I still get this error:
g++ -DPACKAGE_NAME=\"algatorc\" -DPACKAGE_TARNAME=\"algatorc\" -DPACKAGE_VERSION=\"1.0\" -DPACKAGE_STRING=\"algatorc\ 1.0\" -DPACKAGE_BUGREPORT=\"\" -DPACKAGE_URL=\"\" -DPACKAGE=\"algatorc\" -DVERSION=\"1.0\" -I. -g -O2 -MT algatorc.o -MD -MP -MF .deps/algatorc.Tpo -c -o algatorc.o algatorc.cpp
In file included from /usr/include/c++/4.8/thread:35:0,
from Log.hpp:281,
from algatorc.cpp:18:
/usr/include/c++/4.8/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support is currently experimental, and must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
#error This file requires compiler and library support for the \
^
And from this error I can see that g++ doesn't use -Wall -fPIC -std=gnu++11 but I don't see why. It's using something completely else.
This is my configure.ac script which is located in rootdir of my project
AC_PREREQ([2.69])
AC_INIT([algatorc], [0.1], [my_mail])
AC_CONFIG_SRCDIR([src/TestCase.hpp])
#AC_CONFIG_HEADERS([config.h])
LT_INIT
AM_INIT_AUTOMAKE
# Checks for programs.
AC_PROG_CXX
# Checks for libraries.
# Checks for header files.
AC_CHECK_HEADERS([stdlib.h string.h sys/time.h unistd.h wchar.h wctype.h])
# Checks for typedefs, structures, and compiler characteristics.
AC_CHECK_HEADER_STDBOOL
AC_C_INLINE
AC_TYPE_SIZE_T
# Checks for library functions.
AC_FUNC_MALLOC
AC_FUNC_MKTIME
AC_CHECK_FUNCS([gettimeofday memset mkdir])
LIBS=-ldl
AC_CONFIG_FILES([Makefile])
AC_OUTPUT
I have also tried to add AX_CXX_COMPILE_STDCXX_11 to configure.ac script but error still occurs. Any idea how to fix this?
I am using Ubuntu 12.04 x64, and Eclipse (Version: Mars Release (4.5.0))

Answer 1

A quick test shows that everything is working correctly for me, with a similar configuration, so you're going to have to figure out what's going on with your Makefile simply by rolling up your sleeves, looking into your final Makefile.
Look inside the automake-d Makefile. You should find somewhere inside it, the final build rule for .cpp.o. Search for ".cpp.o". It should look something like this:
.cpp.o:
$(AM_V_CXX)$(CXXCOMPILE) -MT $# -MD -MP -MF $(DEPDIR)/$*.Tpo -c -o $# $<
$(AM_V_at)$(am__mv) $(DEPDIR)/$*.Tpo $(DEPDIR)/$*.Po
After verifying this, the next step is to look at what your CXXCOMPILE macro is defined to. It should look something like this:
CXXCOMPILE = $(CXX) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) \
$(AM_CPPFLAGS) $(CPPFLAGS) $(AM_CXXFLAGS) $(CXXFLAGS)
And that's your AM_CXXFLAGS variable being used. Finally, confirm how it's defined in the actual Makefile.
In my case, for my simple test, it was simply:
AM_CXXFLAGS = -std=gnu++11
In my case, it was just that, in your case, obviously you'll have your other flags in there.
That's it. The automake-d Makefile is obviously quite large, and looks intimidating, but when you get down to it, it's not very complicated at all.
It's going to be one of two things. Either another part of your Makefile.am clobbers the value of AM_CXXFLAGS, or the CXXCOMPILE macro is clobbered. One thing about automake, is that it generally doesn't complain if a macro or a variable is redefined. It'll simply generate the final Makefile using the final value of the variable. So, I would guess that somewhere later, in your Makefile.am, you set AM_CXXFLAGS to something else, without being aware of it here.
Note: the actual macros often get tweaked, with each successive version of automake, so yours may look slightly different, but the general idea should be the same. The .cpp.o build rule runs the CXXCOMPILE macro, which uses AM_CXXFLAGS.

Answer 2

First of all, automake will not generate Makefile until executing automake
So, I added -std=gnu++11 for C++11 support but I still get this error:
g++ -DPACKAGE_NAME=\"algatorc\" -DPACKAGE_TARNAME=\"algatorc\" -DPACKAGE_VERSION=\"1.0\" -DPACKAGE_STRING=\"algatorc\ 1.0\" -DPACKAGE_BUGREPORT=\"\" -DPACKAGE_URL=\"\" -DPACKAGE=\"algatorc\" -DVERSION=\"1.0\" -I. -g -O2 -MT algatorc.o -MD -MP -MF .deps/algatorc.Tpo -c -o algatorc.o algatorc.cpp
In file included from /usr/include/c++/4.8/thread:35:0,
from Log.hpp:281,
from algatorc.cpp:18:
/usr/include/c++/4.8/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support is currently experimental, and must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
#error This file requires compiler and library support for the \
^
Your log said there is no statement of -std=gnu++11 in gcc`s compile time. In other words, automake didn't generate Makefile containing statement of -std=gnu++11.
So, all you need to do is, in your project root with command line:
$ autoreconf
This will automatically execute aclocal, autoconf, automake and blah blah...
About checking the -std=c++11 flag
is good to use ax_cxx_compile_stdcxx_11.m4
To use it, you need to download it from the above link and set it in $(project_top)/m4/
Next, you write like below in configure.ac:
AX_CXX_COMPILE_STDCXX_11([noext], [mandatory])
And exec, you can check it's possible or not to use C++11 feature in the platform
$ autoreconf -vi -I m4
$ ./configure