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46 lines
1.8 KiB
Markdown
46 lines
1.8 KiB
Markdown
# CLI11 Internals
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## Callbacks
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The library was designed to bind to existing variables without requiring typed classes or inheritance. This is accomplished through lambda functions.
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This looks like:
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```cpp
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Option* add_option(string name, T item) {
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this->function = [&item](string value){
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item = detail::lexical_cast<T>(value);
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}
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}
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```
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Obviously, you can't access `T` after the `add_` method is over, so it stores the string representation of the default value if it receives the special `true` value as the final argument (not shown above).
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## Parsing
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Parsing follows the following procedure:
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1. `_validate`: Make sure the defined options are self consistent.
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2. `_parse`: Main parsing routine. See below.
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3. `_run_callback`: Run an App callback if present.
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The parsing phase is the most interesting:
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1. `_parse_single`: Run on each entry on the command line and fill the options/subcommands.
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2. `_process`: Run the procedure listed below.
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3. `_process_extra`: This throws an error if needed on extra arguments that didn't fit in the parse.
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The `_process` procedure runs the following steps; each step is recursive and completes all subcommands before moving to the next step (new in 1.7). This ensures that interactions between options and subcommand options is consistent.
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1. `_process_ini`: This reads an INI file and fills/changes options as needed.
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2. `_process_env`: Look for environment variables.
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3. `_process_callbacks`: Run the callback functions - this fills out the variables.
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4. `_process_help_flags`: Run help flags if present (and quit).
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5. `_process_requirements`: Make sure needs/excludes, required number of options present.
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## Exceptions
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The library immediately returns a C++ exception when it detects a problem, such as an incorrect construction or a malformed command line.
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