65 lines
2.9 KiB
Markdown
65 lines
2.9 KiB
Markdown
# Validators
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There are two forms of validators:
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* `transform` validators: mutating
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* `check` validators: non-mutating (recommended unless the parsed string must be mutated)
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A transform validator comes in one form, a function with the signature `std::string(std::string)`.
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The function will take a string and return the modified version of the string. If there is an error,
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the function should throw a `CLI::ValidationError` with the appropriate reason as a message.
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However, `check` validators come in two forms; either a simple function with the const version of the
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above signature, `std::string(const std::string &)`, or a subclass of `struct CLI::Validator`. This
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structure has two members that a user should set; one (`func_`) is the function to add to the Option
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(exactly matching the above function signature, since it will become that function), and the other is
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`name_`, and is the type name to set on the Option (unless empty, in which case the typename will be
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left unchanged).
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Validators can be combined with `&` and `|`, and they have an `operator()` so that you can call them
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as if they were a function. In CLI11, const static versions of the validators are provided so that
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the user does not have to call a constructor also.
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An example of a custom validator:
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```cpp
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struct LowerCaseValidator : public Validator {
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LowerCaseValidator() {
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name_ = "LOWER";
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func_ = [](const std::string &str) {
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if(CLI::detail::to_lower(str) != str)
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return std::string("String is not lower case");
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else
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return std::string();
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};
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}
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};
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const static LowerCaseValidator Lowercase;
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```
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If you were not interested in the extra features of Validator, you could simply pass the lambda function above to the `->check()` method of `Option`.
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The built-in validators for CLI11 are:
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| Validator | Description |
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|---------------------|-------------|
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| `ExistingFile` | Check for existing file (returns error message if check fails) |
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| `ExistingDirectory` | Check for an existing directory (returns error message if check fails) |
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| `ExistingPath` | Check for an existing path |
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| `NonexistentPath` | Check for an non-existing path |
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| `Range(min=0, max)` | Produce a range (factory). Min and max are inclusive. |
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And, the protected members that you can set when you make your own are:
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| Type | Member | Description |
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|------|--------|-------------|
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| `std::function<std::string(std::string &)>` | `func_` | Core validation function - modifies input and returns "" if successful |
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| `std::function<std::string()>` | `desc_function` | Optional description function (uses `description_` instead if not set) |
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| `std::string` | `name_` | The name for search purposes |
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| `int` (`-1`) | `application_index_` | The element this validator applies to (-1 for all) |
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| `bool` (`true`) | `active_` | This can be disabled |
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| `bool` (`false`) | `non_modifying_` | Specify that this is a Validator instead of a Transformer |
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