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Added README entry for flag()

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Pranav Srinivas Kumar 2023-10-27 16:38:53 -05:00
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@ -158,6 +158,31 @@ Here's what's happening:
* Since the argument is actually optional, no error is thrown when running the program without ```--verbose```. Note that by using ```.default_value(false)```, if the optional argument isn’t used, it's value is automatically set to false. * Since the argument is actually optional, no error is thrown when running the program without ```--verbose```. Note that by using ```.default_value(false)```, if the optional argument isn’t used, it's value is automatically set to false.
* By using ```.implicit_value(true)```, the user specifies that this option is more of a flag than something that requires a value. When the user provides the --verbose option, it's value is set to true. * By using ```.implicit_value(true)```, the user specifies that this option is more of a flag than something that requires a value. When the user provides the --verbose option, it's value is set to true.
#### Flag
When defining flag arguments, you can use the shorthand `flag()` which is the same as `default_value(false).implicit_value(true)`.
```cpp
argparse::ArgumentParser program("test");
program.add_argument("--verbose")
.help("increase output verbosity")
.flag();
try {
program.parse_args(argc, argv);
}
catch (const std::exception& err) {
std::cerr << err.what() << std::endl;
std::cerr << program;
std::exit(1);
}
if (program["--verbose"] == true) {
std::cout << "Verbosity enabled" << std::endl;
}
```
#### Requiring optional arguments #### Requiring optional arguments
There are scenarios where you would like to make an optional argument ***required***. As discussed above, optional arguments either begin with `-` or `--`. You can make these types of arguments required like so: There are scenarios where you would like to make an optional argument ***required***. As discussed above, optional arguments either begin with `-` or `--`. You can make these types of arguments required like so: