filesystem not found

[osmanfb]

my ubuntu 18.04 system is using g++7.5 and I am getting
g++ -c -fPIC -I/usr/local/boost_1_75_0 '-I/usr/local/lib/ff++/4.9/include' -g -O2 -DNDEBUG -O3 -mtune=generic -std=c++14 -DBAMG_LONG_LONG -DNCHECKPTR -fPIC -I/usr/local/ff-petsc/r/include -I/usr/include/hdf5/serial -I/usr/include 'webplot.cpp'
webplot.cpp:6:10: fatal error: filesystem: No such file or directory
#include
^~~~~~~~~~~~
compilation terminated.

I inserted g++9 then I get
g++-9 -c -fPIC -I/usr/local/boost_1_75_0 '-I/usr/local/lib/ff++/4.9/include' -g -O2 -DNDEBUG -O3 -mtune=generic -std=c++14 -DBAMG_LONG_LONG -DNCHECKPTR -fPIC -I/usr/local/ff-petsc/r/include -I/usr/include/hdf5/serial -I/usr/include 'webplot.cpp'
webplot.cpp:14:22: error: ‘std::__fs’ has not been declared
14 | using namespace std::__fs::filesystem;
| ^~~~
webplot.cpp:14:28: error: ‘filesystem’ is not a namespace-name
14 | using namespace std::__fs::filesystem;
| ^~~~~~~~~~
webplot.cpp: In function ‘void signalHandler(int)’:
webplot.cpp:47:30: error: ‘directory_iterator’ was not declared in this scope
47 | for (const auto &entry : directory_iterator(path.str()))
| ^~~~~~~~~~~~~~~~~~

am I missing something? Thanks.

[andylee830914]

Filesystem required GCC 8+.
Could you try to add -lstdc++fs as a GCC flag for compiling?

[osmanfb]

sorry for the late reply. Didn't realize github had notifications :-(
Still not working
~/freefem_webplot$ g++-9 -c -fPIC -lstdc++fs -I/usr/local/boost_1_75_0 '-I/usr/local/lib/ff++/4.9/include' -g -O2 -DNDEBUG -O3 -mtune=generic -std=c++14 -DBAMG_LONG_LONG -DNCHECKPTR -fPIC -I/usr/local/ff-petsc/r/include -I/usr/include/hdf5/serial -I/usr/include 'webplot.cpp'
webplot.cpp:14:22: error: ‘std::__fs’ has not been declared
14 | using namespace std::__fs::filesystem;
| ^~~~
webplot.cpp:14:28: error: ‘filesystem’ is not a namespace-name
14 | using namespace std::__fs::filesystem;
| ^~~~~~~~~~
webplot.cpp: In function ‘void signalHandler(int)’:
webplot.cpp:47:30: error: ‘directory_iterator’ was not declared in this scope
47 | for (const auto &entry : directory_iterator(path.str()))
| ^~~~~~~~~~~~~~~~~~