How to call python from c++

I'm Python new comer. I tried to call a python script from c++ like this (in Raspberry Pi).

std::string pythonCommand = "python Callee.py \""+a+"\" "+b;
int res = system(pythonCommand.c_str());

after running I got this.

python: can't open file 'Callee.py': [Errno 2] No such file or directory

But I can run Callee.py with command line successfully and both file stored in same directory.

What was I missing ?