如何接受空值在boost :: program_options [英] How to accept empty value in boost::program_options
问题描述
我使用boost :: program_options库来处理命令行参数。
我需要通过-r选项接受一个文件名,如果它是空的(-r没有params)我需要使用stdin。
desc.add_options()
(replay,r,boost :: program_options :: value< std :: string>(),bla bla bla)
在这种情况下,boost不会接受-r没有参数并抛出异常。
default_value()选项不起作用,即使用户没有给-r选项也会使库返回值。
任何想法如何
请使用 implicit_value
方法,例如 p>
desc.add_options()
(replay,r,po :: value< std :: string& - > implicit_value(stdin),bla bla bla)
0或1个令牌,如果没有提供令牌,它将像提供'stdin'一样工作。当然,你可以选择任何其他隐式值 - 包括空字符串和' - '如mch建议。
I'm using boost::program_options library to process command line params. I need to accept a file name via -r option, in case if it is empty (-r given without params) I need to use stdin.
desc.add_options()
("replay,r", boost::program_options::value<std::string>(), "bla bla bla")
In this case boost wouldn't accept -r without params and throw an exception. default_value () option does not work as well as it would make library return value even if user didn't give -r option.
Any ideas how to work around?
Please use the implicit_value
method, e.g
desc.add_options()
("replay,r", po::value<std::string>()->implicit_value("stdin"), "bla bla bla")
This makes the option accept either 0 or 1 token, and if no tokens are provided, it will act as if 'stdin' was provided. Of course, you can pick any other implicit value -- including empty string and '-' as suggested by mch.
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