FileNotFoundError: [Errno 2] No such file or directory: 'c++': 'c++'

installation
1

I just installed fenics on the ubuntu 18.04.1 LTS following the instructions as follows:

sudo apt-get install software-properties-common
sudo add-apt-repository ppa:fenics-packages/fenics
sudo apt-get update
sudo apt-get install --no-install-recommends fenics

After installed, the python3 -c ‘import fenics’ is proved. However, when I come to the ‘demo_poisson.py’, it failed to run, and the error messages are posted in the following.
What is wrong with it? and how to solve the problem?

====================================================================

The error massage is as follows:

user@user:~/FEniCS/work/documented$ cd poisson/
user@user:~/FEniCS/work/documented/poisson$ ls
demo_poisson.py demo_poisson.py.rst poisson_u.png
user@user:~/FEniCS/work/documented/poisson$ python3 demo_poisson.py
Calling FFC just-in-time (JIT) compiler, this may take some time.
Traceback (most recent call last):
File “demo_poisson.py”, line 90, in
V = FunctionSpace(mesh, “Lagrange”, 1)
File “/usr/lib/python3/dist-packages/dolfin/function/functionspace.py”, line 33, in init
self._init_convenience(*args, **kwargs)
File “/usr/lib/python3/dist-packages/dolfin/function/functionspace.py”, line 100, in _init_convenience
self._init_from_ufl(mesh, element, constrained_domain=constrained_domain)
File “/usr/lib/python3/dist-packages/dolfin/function/functionspace.py”, line 43, in _init_from_ufl
mpi_comm=mesh.mpi_comm())
File “/usr/lib/python3/dist-packages/dolfin/jit/jit.py”, line 47, in mpi_jit
return local_jit(*args, **kwargs)
File “/usr/lib/python3/dist-packages/dolfin/jit/jit.py”, line 97, in ffc_jit
return ffc.jit(ufl_form, parameters=p)
File “/usr/lib/python3/dist-packages/ffc/jitcompiler.py”, line 217, in jit
module = jit_build(ufl_object, module_name, parameters)
File “/usr/lib/python3/dist-packages/ffc/jitcompiler.py”, line 133, in jit_build
generate=jit_generate)
File “/usr/lib/python3/dist-packages/dijitso/jit.py”, line 178, in jit
params)
File “/usr/lib/python3/dist-packages/dijitso/build.py”, line 153, in build_shared_library
status, output = get_status_output(cmd)
File “/usr/lib/python3/dist-packages/dijitso/system.py”, line 41, in _get_status_output_subprocess
stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
File “/usr/lib/python3.6/subprocess.py”, line 709, in init
restore_signals, start_new_session)
File “/usr/lib/python3.6/subprocess.py”, line 1344, in _execute_child
raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: ‘c++’: ‘c++’

2

See here