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## Class tribool

boost::logic::tribool — A 3-state boolean type.

## Synopsis

    class tribool {
    public:
      // construct/copy/destruct
      tribool();
      tribool(bool);
      tribool(indeterminate_keyword_t);

      // public member functions
      operator safe_bool() const;

      enum boost::logic::tribool::value_t value;
    };

## Description

3-state boolean values are either true, false, or indeterminate.

### `tribool` construct/copy/destruct

1.     tribool();

   Construct a new 3-state boolean value with the value 'false'.

   Throws: Will not throw.

2.     tribool(bool value);

   Construct a new 3-state boolean value with the given boolean value, which may be `true` or `false` .

   Throws: Will not throw.

3.     tribool(indeterminate_keyword_t );

   Construct a new 3-state boolean value with an indeterminate value.

   Throws: Will not throw.

### `tribool` public member functions

1.     operator safe_bool() const;

   Use a 3-state boolean in a boolean context. Will evaluate true in a boolean context only when the 3-state boolean is definitely true.

   Returns: true if the 3-state boolean is true, false otherwise
   Throws: Will not throw.

| Copyright © 2002-2004 Douglas Gregor