# NAG CPP Interfaceutility::Optional

## ▸▿ Contents

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CPP Name Style:

``` #include "include/utility/nagcpp_utility_optional.hpp"

class Optional```

## 1Description

The base class for all optional argument classes included in the interface of all functions in the NAG CPP Interface.
See Optional Arguments for information on classes derived from this class.

## 2Variables

### 2.1Public Variables

$\mathbf{default_to_col_major}$ bool Scalar
If true then the default storage order is assumed to be column-major order, otherwise it is assumed to be row-major order. This value is only used if either:
1. (a) None of the data container arguments have implemented the is_col_major method, or
2. (b) The function in question has a multi-dimensional array in a callback function, but no multi-dimensional array in the main function interface.
This defaults to true.
$\mathbf{fail}$ ErrorHandler Scalar
Error handling class. By default the error handling behaviour is controlled by GLOBAL_ERROR_HANDLER_CONTROL.
$\mathbf{iomanager}$ IOManagerBase Scalar
Input/Output management class. By default this is set to GLOBAL_IOMANAGER.

None.