How to compile multiple files in ROOT

Question

I wrote a C++ program (with a main.cpp, and various header and implementation files) that compiles fine under g++. Now I am trying to compile it in Cern's ROOT library, but I do not know how to, since the only way I know how to compile files in ROOT is by using .L main.cpp.

How can I include multiple files in ROOT?

Answer 1

The most reliable way to use ROOT (at least historically and currently) is to ignore the interpreter other than for the simplest explorations and explicitly compile your C++ programs against the ROOT libraries. For example, use

g++ MySource.cc `root-config --libs --cflags` -o foo

to compile an executable "foo" from a single source file. For more info on that helper script run "root-config --help".

Multi-file programs/libraries are nothing special provided that you supply the required args to point at the ROOT libraries and headers (and that the libs are available in LD_LIBRARY_PATH at runtime.) Standard C++ guides will explain that step if needed. You can safely put this into a makefile, too.

For my money this is both easier and more reliable than using the .L etc. commands in the CINT interpreter. Last time I tried, ACLiC was actually compiling against a temporary (and mangled) version of the specified source file, so any error messages from the compiler were pretty much useless!

Answer 2

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/

Then

cd build
cmake ..

Your binaries will be located in build/bin/ directory

Hope this helps.

Answer 3

It appears that I would simply .L <filename> for each file I want, since .L tells ROOT to "load the contents of file in memory." Though now I am not too sure which order to load the files in, as they are giving me errors.