How to compile multiple files in ROOT

I working on trying to compile a code written in C++ and Root on my Mac. The code is from a colleague who works on a Linux laptop. In addition to the different OS’s, I have both a different version of gcc and Root than her and I am not sure which difference is causing the code not to compile on my machine.

She has g++ 4.8 and root 5.(something). I have gcc 5.3.0 and root 6.06/02.

She has given to me the a line of code she uses to get her machine to compile the code

gcc -Wall -o executable_name code_name.cc `root-config --cflags --glibs`

But when I write on my machine, Terminal gives me the error

gcc: error: unrecognized command line option ‘-stdlib=libc++’
gcc: error: unrecognized command line option ‘-stdlib=libc++’

I need help generating the correct line to get gcc to compile the code.

asked Jul 4, 2016 at 9:20

The problem here is two-fold: You’re on OSX and you are using GCC.

The problem with this is that root-config assumes that since you’re on OSX you will be using the OSX-standard Clang compiler which have the -stdlib flag. Since you’re not using Clang, but GCC (which doesn’t have this flag) you get an error.

You have two possible solutions: Use clang++ instead of g++ to compile and build (requires you to install the compiler if it’s not installed already, it comes with Xcode), or to modify the root-config script so it doesn’t add -stdlib=libc++. There might be environment variables or flags that the root-config script checks that alter the behavior, but I don’t know anything about the script, you have to check it for that.

answered Jul 4, 2016 at 9:28

I use CMake to compile my ROOT-based projects.
If you have a project directory proj/ and it contains src/ and bin/, you’ll need 3 CMakeList.txt files, one in each directory.

A simple example CMakeList.txt in the main project directory:

cmake_minimum_required(VERSION 2.6)
project (SOME_PROJ_NAME)
add_subdirectory(src)
add_subdirectory(bin)

src/ directory is where you keep your .h and .cxx proj. library files. Example CMakeList.txt file:

# get all the *.cxx filenames, to compile them into a lib
file(GLOB SOME_PROJ_LIB_SRCS "${PROJECT_SOURCE_DIR}/src/*.cxx")
# include ROOT library and include files
include_directories(/path/to/root/dir/include/dir)
link_directories(/path/to/root/dir/lib/dir)
# and compile src into a library
add_library(Proj_lib_name ${SOME_PROJ_LIB_SRCS})
# here, list the ROOT libraries you require
target_link_libraries(Proj_lib_name dl Core Cint RIO Net Hist Graf Graf3d Gpad Tree Rint Postscript Matrix Physics MathCore Thread Gui pthread m)

bin/ directory is where you keep your app .cxx files and it has a CMakeList.txt file:

include_directories(${PROJECT_SOURCE_DIR}/src)
link_directories(${PROJECT_SOURCE_DIR}/src)
include_directories(/path/to/root/dir/include/dir)
link_directories(/path/to/root/dir/lib/dir)
add_executable(example_app.exe example_app.cxx)
target_link_libraries(example_app.exe Proj_lib_name dl Core Cint RIO Net Hist Graf Graf3d Gpad Tree Rint Postscript Matrix Physics MathCore Thread Gui pthread m)

Finally, to compile ROOT-based code with CMake, out of source, you create a «build» dir in your top level project dir, so that your dir structure looks like this:

proj/
  bin/
  build/
  src/

cd build
cmake ..

Your binaries will be located in build/bin/ directory

Hope this helps.

Apparently, CERN’s «Root» software is compatible (as of version 6.12) with C++17. However, I have been completely unable to get this to work with the newest version (6.20) and all previous questions I found on this topic are from a few years ago.

Does anyone with Root experience know if there is a particular compiler option to get it to work with C++17?

Examples of errors I get when trying to compile a trivial «Hello world» program:

• The following is (I think) due to the «TFile.h» header implicitly loading «TString.h»:

/usr/local/bin/root_v6.20.02/include/ROOT/RStringView.hxx:32:84: error: conflicting declaration of template ‘template<class _CharT, class _Traits> using basic_string_view = std::experimental::__ROOT::basic_string_view<_CharT, _Traits>

• An example of another (more mysterious, to me at least) error is:

/usr/include/c++/7/ext/concurrence.h:53:16: error: ‘_Lock_policy’ does not name a type                            
   static const _Lock_policy __default_lock_policy =                                                              
                ^~~~~~~~~~~~                                                                                      
In file included from /usr/include/c++/7/iostream:38:0,                                                           
                 from test.cpp:1:                                                                                 
/usr/include/c++/7/ext/concurrence.h: In function ‘void std::__throw_concurrence_lock_error()’:                   
/usr/include/c++/7/ext/concurrence.h:102:5: error: ‘__concurrence_lock_error’ was not declared in this scope      
   { _GLIBCXX_THROW_OR_ABORT(__concurrence_lock_error()); }                                                       
     ^                                                                                                            
/usr/include/c++/7/ext/concurrence.h:102:5: note: suggested alternative:                                          
In file included from /usr/include/c++/7/memory:74:0,                                                             
                 from /usr/local/bin/root_v6.20.02/include/ROOT/TypeTraits.hxx:15,                                
                 from /usr/local/bin/root_v6.20.02/include/TString.h:29,                                          
                 from /usr/local/bin/root_v6.20.02/include/TNamed.h:26,                                           
                 from /usr/local/bin/root_v6.20.02/include/TKey.h:15,                                             
                 from /usr/local/bin/root_v6.20.02/include/TBasket.h:28,                                          
                 from /usr/local/bin/root_v6.20.02/include/ROOT/TIOFeatures.hxx:14,                               
                 from /usr/local/bin/root_v6.20.02/include/TTree.h:30,                                            
                 from /usr/local/bin/root_v6.20.02/include/TNtuple.h:24,                                          
                 from test.cpp:2:                                                                                 
/usr/include/c++/7/ext/concurrence.h:67:9: note:   ‘__gnu_cxx::__concurrence_lock_error’                          
   class __concurrence_lock_error : public std::exception 

CXX = g++
CXXFLAGS = -march=native `root-config --cflags --libs` -std=c++17
LDFLAGS = `root-config --cflags --libs`

Any comments about a possible workaround would be appreciated, or perhaps there is some additional option I need to add in the Makefile? It would also be helpful to know if it is advisable to stick to C++11/14 when using Root libraries.

export ROOTSYS=/Users/petrstepanov/root-6.04.08
export PATH=$ROOTSYS/bin:$PATH
export LD_LIBRARY_PATH=$ROOTSYS/lib:$LD_LIBRARY_PATH
export DYLD_LIBRARY_PATH=$ROOTSYS/lib:$DYLD_LIBRARY_PATH

g++ `root-config --cflags --libs` -L $ROOTSYS/lib -lRooFit -lRooFitCore -lHtml -lMinuit -lFumili your-program-name.cpp -o your-program-name.o

./your-program-name.o