Parsing common data types

Often a command line argument or option value needs to be converted into a specific data type inside your application code. Examples include converting an argument into an integer, an enum or a floating point number. You can, of course, relatively easily perform such a conversion yourself using whatever facilities you prefer. However, doing it in C++ safely and correctly is often unnecessarily hard. To help with this Argument provides a few type parsers - utility functions or classes to simplify such common tasks.

If you are not using single-header (or module) distribution these parsers are available in <argum/type-parsers.h> header.

Parsing Integers

Function template parseIntegral<Type> allows you to convert a string_view/wstring_view into any integral type. The format it accepts is as follows

• Any number of spaces followed by
• A number recognized by the family of strtoX standard functions (see here and here). The number must fit into the destination type.
• Any number of spaces

The second argument to parseIntegral is "base" which operates exactly like the "base" argument of strtoX family of functions. By default it is 0 - meaning "guess based on prefix".

If the format cannot be parsed the function throws Parser::ValidationError. Otherwise it returns the parsed integral. Here is an example:

unsigned short aNumber;
...
parser.add(
    Positional("number").
    help("a number"). 
    handler([&](const std::string_view & value) { 
        aNumber = parseIntegral<unsigned short>(value);
}));

Parsing Floating Point Numbers

Very similar to the above there is also parseFloatingPoint<Type> that can parse float, double or long double. It operates almost identically except the parsing format is the one of strtof family of functions.

Parsing Enumerations or Choices

Very often an argument or option value must be a choice between different fixed options. The choices might map to some actual enum in application code or just be some fixed allowed values. To complicate matters, sometimes multiple command line choices (or alternative spellings) must map to a single entry in program code.

To deal with all that Argum provides ChoiceParser (and WChoiceParser) class.