C++ gflags

bool类型的
DEFINE_bool(bool_flag, true, "one bool_flag");
DEFINE_string(animals, "bird,cat,dog", "comma-separated list of animals");

运行时，比如./app可以加后缀：
app -bool_flag
app -nobool_flag 相当于bool_flag=false
app -bool_flag=true
app -bool_flag=false