g++ --coverage demo.cpp # demo.gcno
./a.out   # demo.gcda
gcov demo # demo.cpp.gcov
cat demo.cpp.gcov

lcov --rc lcov_branch_coverage=1 -c -d . -o demo_lcov_report
#all
#genhtml --rc genhtml_branch_coverage=1 demo_lcov_report -o out_report
#filter
lcov --rc lcov_branch_coverage=1 -r demo_lcov_report '/usr/include/*' '*lib/*' -o filtered_coverage
genhtml --rc genhtml_branch_coverage=1 filtered_coverage -o filtered_out_report