Unexpected behavior when setting two `std::vector` values as positional arguments

[TrainFan1804]

Description

I wanted set two std::vector options as positional arguments and tried following code:

options
    .add_options()
    ("f,foo", "foo", cxxopts::value<std::vector<std::string>>(), "foo")
    ("b,bar", "bar", cxxopts::value<std::vector<std::string>>(), "bar");

options.parse_positional({"foo", "bar"});

when I run

./a.out --bar a b c

I expected bar to be [a, b, c] and foo to be empty but I actually got.

bar = a
foo = b
foo = c

Expected

Non-option arguments following a option (--bar) should not be assigned as a positional parameter.

Conclusion

If this is desired behavior it would be helpful if it was clarified in the README.md.
If not I guess it may be a parsing bug.

[jarro2783]

I think this is expected. When you specifically specify --bar you are only adding argument to it, not everything that follows. Then the unnamed arguments following are treated as positional arguments, which are read into foo since it is the first positional argument.
Note that a vector positional argument like foo also means that the later ones will never match because foo will swallow up all arguments.

[lazysegtree]

@TrainFan1804 Yes that is the desired behaviour. I see that Readme states that clearly.

If this is desired behavior it would be helpful if it was clarified in the README.md.

README has the below line in https://github.com/jarro2783/cxxopts?tab=readme-ov-file#stdvectort-values . I think that clarifies it.

Ensure that you use no whitespaces between values (unless the entire list is double quoted) because those would be interpreted as the next command line option

Can you propose a clear change in README that will clarify it even further? I think there is no update needed.