Bad compilation command from autoconf test - c++

I'm trying to write an autoconf test for a C++ library. I followed http://nerdland.net/2009/07/detecting-c-libraries-with-autotools/ . My check looks like this:
SAVED_LDFLAGS=$LDFLAGS
LDFLAGS="$LDFLAGS -lMyLib"
AC_LINK_IFELSE(
[AC_LANG_PROGRAM([#include <mylibheader.hpp>],
[MyLibNamespace::SomeObject obj()])],
[TEST_LIBS="$TEST_LIBS -lMyLib"] [HAVE_MYLIB=1],
[AC_MSG_ERROR([libMyLib is not installed.])])
LDFLAGS=$SAVED_LDFLAGS
The test fails. If i check config.log the problem seems to be with the generated compilation command given by autoconf for the check:
g++ -o conftest -g -O2 -lMyLib conftest.cpp
As you can see, the -l params aren't at the end, after all inputs and outpus. If i copy&paste the conftest.cpp code from config.log i can make it compile with:
g++ -o conftest -g -O2 conftest.cpp -lMyLib
How can autoconf be wrong? How may i fix this?

The problem is that you're adding -lMyLib to LDFLAGS instead of adding to LIBS. In other words, do this instead:
SAVED_LIBS=$LIBS
LIBS="-lMyLib $LIBS"
AC_LINK_IFELSE(
[AC_LANG_PROGRAM([#include <mylibheader.hpp>],
[MyLibNamespace::SomeObject obj()])],
[TEST_LIBS="$TEST_LIBS -lMyLib"] [HAVE_MYLIB=1],
[AC_MSG_ERROR([libMyLib is not installed.])])
LIBS=$SAVED_LIBS
Edit: link order of libraries is important, so I've updated the LIBS= line to link MyLib before the other libraries, if any, with the assumption that MyLib may depend on other libraries.

Related

C++ file compiling: -L and -I arguments don't work for boost library

There are similar questions but their answers did not work for my issue.
I have a c++ program with #include <boost/test/unit_test.hpp> on top (among other includes).
To compile correctly, if I understood, I should do the command:
g++ -g -L/path_to_boost_lib -lboost_lib myprog.cpp -o myprog.exe
If i do a locate, I get /usr/lib/x86_64-linux-gnu/libboost_unit_test_framework.so.
Hence I edited my call to g++ by doing:
g++ -g -L/usr/lib/x86_64-linux-gnu -lboost_unit_test_framework myprog.cpp -o myprog.exe
But I still get errors of the type undefined reference to boost::unit_test.
I also tried the option -I/usr/include/ which contains the boost folder, without success.
It's because of the order. The GCC linker goes through the artifacts left-to-right, and every unknown symbol it encounters in an object file must be resolved by an artifact occurring afterwards.
The right command is thus:
g++ -g myprog.cpp -L/usr/lib/x86_64-linux-gnu -lboost_unit_test_framework -o myprog.exe
See this answer for a more thorough explanation.
I suggest using a build tool like CMake that takes care of such low-level details for you.

Getting Cplex example to run: Undefined references

I am trying to get the Cplex basic LP example to work. The code can be found here. I am completely new with c++, but hope to be able to get this running.
I am trying to compile it on linux. I am using the following command to run it
g++ -D IL_STD -I /opt/ibm/ILOG/CPLEX_Studio1271/opl/include ilolpex1.cpp
The -D IL_STD was put there to solve an error as found here. The -I ... was put there to specify the location of the header files. I came up with this myself after a lot of trying and googling, so i am in no way sure this is correct.
Anyway, i when i run it i get errors of undefined references:
/tmp/ccl9O1YF.o: In function `populatebyrow(IloModel, IloNumVarArray, IloRangeArray)':
ilolpex1.cpp:(.text+0x18f): undefined reference to `IloNumVar::IloNumVar(IloEnv, double, double, IloNumVar::Type, char const*)'
I did not make any changes in the file, so i assume the only thing which can be wrong is how the files are linked. I have the feeling it probably just is a simple setting, but after hours of looking i still have no idea how to fix it.
The easiest way to compile the ilolpex1.cpp example is to use the Makefile that is included with the installation. For example, you should do the following:
$ cd /opt/ibm/ILOG/CPLEX_Studio1271/cplex/examples/x86-64_linux/static_pic
$ make ilolpex1
This will produce output, like the following:
g++ -O0 -c -m64 -O -fPIC -fno-strict-aliasing -fexceptions -DNDEBUG -DIL_STD -I../../../include -I../../../../concert/include ../../../examples/src/cpp/ilolpex1.cpp -o ilolpex1.o
g++ -O0 -m64 -O -fPIC -fno-strict-aliasing -fexceptions -DNDEBUG -DIL_STD -I../../../include -I../../../../concert/include -L../../../lib/x86-64_linux/static_pic -L../../../../concert/lib/x86-64_linux/static_pic -o ilolpex1 ilolpex1.o -lconcert -lilocplex -lcplex -lm -lpthread
This will tell you everything you'll need to know if you choose to compile your own application by hand in the future. The details about this are described in the documentation (e.g., here).
Obviously, the iloplex1.cpp file is just a demo how to use IloCplex.
What you yet need is IloCplex itself. This should come either as (a) further source file(s) you have to compile with the demo or as a library you link against.
Have a look at your cplex directories, you might find a lib[...].a file somewhere there, possibly in /opt/ibm/ILOG/CPLEX_Studio1271/opl/lib.
You can link against using GCC's (clang's) -l and -L options. Be aware that when using -l, you leave out lib and .a (-l [...] with above (invalid) sample name).

How do I apply a flag to a library in SCons?

I need to execute a build command similar to:
g++ -Wl,-rpath=../libs source.o -static -Wl,-Bdynamic -ldynlib -Wl,-Bstatic -lstaticlib
My current (wrong) SConscript links in dynlib with this line:
env.AppendUnique(LINKFLAGS=['-Wl,-Bdynamic', '-ldynlib']);
However when I run scons, I get this:
g++ -Wl,-rpath=../libs -static -Wl,-Bdynamic -ldynlib source.o -Wl,-Bstatic -lstaticlib
Because source.o is after dynlib, it can't find dynlib, and this causes link errors. The solution (verified manually) is to move source.o before dynlib, which is a vendor-provided library.
Ideally I'd add dynlib to LIBS but SCons does not appear to support flags there.
What workaround can I use to get SCons to generate the correct build line?
Literal turned out to be the solution. For whatever reason, SCons doesn't prepend '-l' to my flags now.
env['FORCEDYNAMIC'] = env.Literal('-Wl,-Bdynamic')
env.PrependUnique(LIBS = [['${FORCEDYNAMIC}', 'dynlib']])

mingw g++ is unable to link with libraries

I'm trying to use X86_64-w64-mingw32-g++ (packaged in Archlinux's MingW package) to cross compile some C++ code into an Windows executable, however I'm having trouble getting past some issues.
I'm calling
x86_64-w64-mingw32-g++ -o build_win/asm build_win/asm.o build_win/asm_lib.o build_win/socket_boost.o -I../extra/etc -fopenmp -lrt -std=c++11 -g -lboost_system -lboost_serialization
from a makefile, but I get thrown the errors:
/usr/lib/gcc/x86_64-w64-mingw32/5.1.0/../../../../x86_64-w64-mingw32/bin/ld: cannot find -lrt
/usr/lib/gcc/x86_64-w64-mingw32/5.1.0/../../../../x86_64-w64-mingw32/bin/ld: cannot find -lboost_system
/usr/lib/gcc/x86_64-w64-mingw32/5.1.0/../../../../x86_64-w64-mingw32/bin/ld: cannot find -lboost_serialization
This works fine with native g++, so exactly do I have to change for mingw to compile?
EDIT: I have mingw-w64-boost package installed, which includes boost libraries pre-compiled and ready to be linked. However, it seems the naming convention is a bit different, and -lboost_system for example becomes -llibboost_system-mt (not exactly sure what the -mt suffix entails).
Problem is I can't find the mingw counterpart for -lrt. I've tried with both -lrtm and -lrtutils but in both cases I get:
[...]
undefined reference to `__imp_getsockopt'
Are you sure that -lboost_system and other libraries are present in the same directory as makefile ?
If not then please include -L flag which indicates the location of your library.
For example:
-L /path_openmp -fopenmp -L /path_boost_system/ -lboost_system -L /path_serialization -lboost_serialization
Moreover, you need not include -I and -g flag when creating an executable from .o files. These are needed when you create .o from .cpp files.
There is no rt library on Windows.
You are missing -lws2_32.
$ x86_64-w64-mingw32-nm -A /usr/x86_64-w64-mingw32/lib/*.a 2>/dev/null | grep getsockopt | grep " T "

g++ linking static and non-static libraries at the same time

I have a makefile project in which I include a few different libraries. One of them is the boost library which I statically link in order to make my program portable. This is how my makefile command looks like:
g++ -O0 -g test.cpp testObject.o -pthread -I/home/user/devel/lmx-sdk-4.7.1/include/ -L/home/user/devel/lmx-sdk-4.7.1/linux_x64 -llmxclient -lrt -ldl -lboost_filesystem -lboost_system -static -static-libgcc -o $#
I have also linked lmx-sdk library to my project in order to use the licensing functionality; however, it seems to be that lmx-sdk doesn't seem to like static link as it gives an error "Using 'dlopen' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking".
How can I make it possible to link some libraries statically and the other ones dynamically ?
Thanks in advance
P.S. I have checked some of similar topics and tried a few methods which didn't work out for me.
Using -Wl,-Bdynamic and -Wl,-Bstatic instead of just using -Bdynamic and -Bstatic solved the problem.
The full link line looks like this now:
g++ -O0 -g test.cpp testObject.o -pthread -Bdynamic -I/home/user/devel/lmx-sdk-4.7.1/include/ -L/home/user/devel/lmx-sdk-4.7.1/linux_x64 -llmxclient -lrt -ldl -Wl,-Bstatic -lboost_filesystem -lboost_system -o $#
You can use -Bstatic to statically link what comes after it, then -Bdynamic to do the opposite. As many times as you need on the command line.