Problems linking TFormula in shared library

[VukanJ]

---

ROOT Version: 6.16.00
Platform: CentOS 7
Compiler: g++ 7.3.1 20180303

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Dear experts,
In the following minimal example i am trying to build a shared library including TFormula.
When i run the MyClass::dev() method from the shared library in python, I get the error

python: symbol lookup error:<PATH_TO>myclass.so: undefined symbol: _ZN8TFormulaC1EPKcS1_bb

MyClass.h:

    #ifndef MYCLASS_H
    #define MYCLASS_H
    #include "TFormula.h"

    class MyClass {
    public:
        MyClass() {}
        virtual ~MyClass() {}
        void dev();
    private:
        ClassDef(MyClass,1)
    };
    #endif

MyClass.cxx

    #include "Riostream.h"
    #include "MyClass.h"

    void MyClass::dev() 
    {
        TFormula f("F", "[0]**2+[1]**2");
    }

MyClass_LinkDef.h

    #ifdef __CINT__
    #pragma link off all globals;
    #pragma link off all classes;
    #pragma link off all functions;
    #pragma link C++ nestedclasses;
    #pragma link C++ defined_in "MyClass.h";
    #endif

My makefile produces the following commands:

g++ -Wall -Wextra -Woverloaded-virtual -fPIC -W -pipe -Ofast -ftree-vectorize  -pthread -std=c++17 -m64 -I/usr/local/include/root -L/usr/local/lib/root -lCore -lImt -lRIO -lNet -lHist -lGraf -lGraf3d -lGpad -lROOTVecOps -lTree -lTreePlayer -lRint -lPostscript -lMatrix -lPhysics -lMathCore -lThread -lMultiProc -lROOTDataFrame -pthread -Wl,-rpath,/usr/local/lib/root -lm -ldl -rdynamic -lRooFit -lRooStats -lTreePlayer  -c MyClass.cxx -o MyClass.o

rootcint -f myclass_dict.cc -c MyClass.h MyClass_LinkDef.h

g++ -Wall -Wextra -Woverloaded-virtual -fPIC -W -pipe -Ofast -ftree-vectorize  -pthread -std=c++17 -m64 -I/usr/local/include/root -L/usr/local/lib/root -lCore -lImt -lRIO -lNet -lHist -lGraf -lGraf3d -lGpad -lROOTVecOps -lTree -lTreePlayer -lRint -lPostscript -lMatrix -lPhysics -lMathCore -lThread -lMultiProc -lROOTDataFrame -pthread -Wl,-rpath,/usr/local/lib/root -lm -ldl -rdynamic -lRooFit -lRooStats -lTreePlayer -c myclass_dict.cc -I. -o myclass_dict.o

g++ -shared -O3  MyClass.o myclass_dict.o -o myclass.so

Why does TFormula not link properly even though I have included all libraries that are required for TFormula?
Here is an example of the script I am using:

    import ROOT
    from ROOT import gSystem
    gSystem.Load("myclass.so")

    m = ROOT.MyClass() # No problem so far
    m.dev() # Error from above

[etejedor]

Hi @VukanJ

You need to include your header before loading the library.

import ROOT
from ROOT import gSystem, gInterpreter
gInterpreter.ProcessLine('#include "MyClass.h"')
gSystem.Load("myclass.so")

[etejedor]

Also please note that ROOT 6 does not use cint anymore, so you do not need MyClass_LinkDef and its related step in the makefile. You just need to generate your .so by linking it to ROOT and then run your Python script as described.

[VukanJ]

Yes, that works perfectly, thank you! And thanks for the tip!