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# Exiv2::Key Class Reference

Abstract base class defining the Key of a metadatum. Keys are used to identify and group metadata. More...

`#include <metadatum.hpp>`

Inheritance diagram for Exiv2::Key:

[legend]
List of all members.

## Public Types
typedef std::auto_ptr< Key > | AutoPtr
| Shortcut for a Key auto pointer.
## Public Member Functions
Creators
virtual | ~Key ()
| Destructor.
Accessors
virtual std::string | key () const =0
| Return the key of the metadatum as a string. The key is of the form 'familyName.groupName.tagName'. Note however that the key is not necessarily unique, e.g., an ExifData may contain multiple metadata with the same key.
virtual const char * | familyName () const =0
| Return an identifier for the type of metadata (the first part of the key).
virtual std::string | groupName () const =0
| Return the name of the group (the second part of the key).
virtual std::string | tagName () const =0
| Return the name of the tag (which is also the third part of the key).
virtual std::string | tagLabel () const =0
| Return a label for the tag.
virtual uint16_t | tag () const =0
| Return the tag number.
AutoPtr | clone () const
| Return an auto-pointer to a copy of itself (deep copy). The caller owns this copy and the auto-pointer ensures that it will be deleted.
std::ostream & | write (std::ostream &os) const
| Write the key to an output stream. You do not usually have to use this function; it is used for the implementation of the output operator for Key, operator<<(std::ostream &os, const Key &key).
## Protected Member Functions
Manipulators
Key & | operator= (const Key &rhs)
| Assignment operator. Protected so that it can only be used by subclasses but not directly.

## Detailed Description

Abstract base class defining the Key of a metadatum. Keys are used to identify and group metadata.

The documentation for this class was generated from the following files:

- metadatum.hpp
- metadatum.cpp