class Poco::TextEncoding

Overview

An abstract base class for implementing text encodings like UTF-8 or ISO 8859-1. More…

#include <TextEncoding.h>

class TextEncoding
{
public:
    // typedefs

    typedef SharedPtr<TextEncoding> Ptr;
    typedef int CharacterMap[256];

    // enums

    enum
    {
        MAX_SEQUENCE_LENGTH = 6,
    };

    // fields

    static const std::string GLOBAL;

    // methods

    virtual
    const char*
    canonicalName() const = 0;

    virtual
    bool
    isA(const std::string& encodingName) const = 0;

    virtual
    const CharacterMap&
    characterMap() const = 0;

    virtual
    int
    convert(const unsigned char* bytes) const;

    virtual
    int
    queryConvert(
        const unsigned char* bytes,
        int length
        ) const;

    virtual
    int
    sequenceLength(
        const unsigned char* bytes,
        int length
        ) const;

    virtual
    int
    convert(
        int ch,
        unsigned char* bytes,
        int length
        ) const;

    static
    TextEncoding&
    byName(const std::string& encodingName);

    static
    TextEncoding::Ptr
    find(const std::string& encodingName);

    static
    void
    add(TextEncoding::Ptr encoding);

    static
    void
    add(
        TextEncoding::Ptr encoding,
        const std::string& name
        );

    static
    void
    remove(const std::string& encodingName);

    static
    TextEncoding::Ptr
    global(TextEncoding::Ptr encoding);

    static
    TextEncoding&
    global();

protected:
    // methods

    static
    TextEncodingManager&
    manager();
};

// direct descendants

class ASCIIEncoding;
class Latin1Encoding;
class Latin2Encoding;
class Latin9Encoding;
class UTF16Encoding;
class UTF32Encoding;
class UTF8Encoding;
class Windows1250Encoding;
class Windows1251Encoding;
class Windows1252Encoding;

Detailed Documentation

An abstract base class for implementing text encodings like UTF-8 or ISO 8859-1.

Subclasses must override the canonicalName(), isA(), characterMap() and convert() methods and need to be thread safe and stateless.

TextEncoding also provides static member functions for managing mappings from encoding names to TextEncoding objects.

Enum Values

MAX_SEQUENCE_LENGTH

The maximum character byte sequence length supported.

Typedefs

typedef int CharacterMap[256]

The map[b] member gives information about byte sequences whose first byte is b.

If map[b] is c where c is >= 0, then b by itself encodes the Unicode scalar value c. If map[b] is -1, then the byte sequence is malformed. If map[b] is -n, where n >= 2, then b is the first byte of an n-byte sequence that encodes a single Unicode scalar value. Byte sequences up to 6 bytes in length are supported.

Fields

static const std::string GLOBAL

Name of the global TextEncoding, which is the empty string.

Construction

virtual
~TextEncoding()

Destroys the encoding.

Methods

virtual
const char*
canonicalName() const = 0

Returns the canonical name of this encoding, e.g.

“ISO-8859-1”. Encoding name comparisons are case insensitive.

virtual
bool
isA(const std::string& encodingName) const = 0

Returns true if the given name is one of the names of this encoding.

For example, the “ISO-8859-1” encoding is also known as “Latin-1”.

Encoding name comparision are be case insensitive.

virtual
const CharacterMap&
characterMap() const = 0

Returns the CharacterMap for the encoding.

The CharacterMap should be kept in a static member. As characterMap() can be called frequently, it should be implemented in such a way that it just returns a static map. If the map is built at runtime, this should be done in the constructor.

virtual
int
convert(const unsigned char* bytes) const

The convert function is used to convert multibyte sequences; bytes will point to a byte sequence of n bytes where sequenceLength(bytes, length) == -n, with length >= n.

The convert function must return the Unicode scalar value represented by this byte sequence or -1 if the byte sequence is malformed. The default implementation returns (int) bytes[0].

virtual
int
queryConvert(
    const unsigned char* bytes,
    int length
    ) const

The queryConvert function is used to convert single byte characters or multibyte sequences; bytes will point to a byte sequence of length bytes.

The queryConvert function must return the Unicode scalar value represented by this byte sequence or -1 if the byte sequence is malformed or -n where n is number of bytes requested for the sequence, if lenght is shorter than the sequence. The length of the sequence might not be determined by the first byte, in which case the conversion becomes an iterative process: First call with length == 1 might return -2, Then a second call with lenght == 2 might return -4 Eventually, the third call with length == 4 should return either a Unicode scalar value, or -1 if the byte sequence is malformed. The default implementation returns (int) bytes[0].

virtual
int
sequenceLength(
    const unsigned char* bytes,
    int length
    ) const

The sequenceLength function is used to get the lenth of the sequence pointed by bytes.

The length paramater should be greater or equal to the length of the sequence.

The sequenceLength function must return the lenght of the sequence represented by this byte sequence or a negative value -n if length is shorter than the sequence, where n is the number of byte requested to determine the length of the sequence. The length of the sequence might not be determined by the first byte, in which case the conversion becomes an iterative process as long as the result is negative: First call with length == 1 might return -2, Then a second call with lenght == 2 might return -4 Eventually, the third call with length == 4 should return 4. The default implementation returns 1.

virtual
int
convert(
    int ch,
    unsigned char* bytes,
    int length
    ) const

Transform the Unicode character ch into the encoding’s byte sequence.

The method returns the number of bytes used. The method must not use more than length characters. Bytes and length can also be null - in this case only the number of bytes required to represent ch is returned. If the character cannot be converted, 0 is returned and the byte sequence remains unchanged. The default implementation simply returns 0.

static
TextEncoding&
byName(const std::string& encodingName)

Returns the TextEncoding object for the given encoding name.

Throws a NotFoundException if the encoding with given name is not available.

static
TextEncoding::Ptr
find(const std::string& encodingName)

Returns a pointer to the TextEncoding object for the given encodingName, or NULL if no such TextEncoding object exists.

static
void
add(TextEncoding::Ptr encoding)

Adds the given TextEncoding to the table of text encodings, under the encoding’s canonical name.

If an encoding with the given name is already registered, it is replaced.

static
void
add(
    TextEncoding::Ptr encoding,
    const std::string& name
    )

Adds the given TextEncoding to the table of text encodings, under the given name.

If an encoding with the given name is already registered, it is replaced.

static
void
remove(const std::string& encodingName)

Removes the encoding with the given name from the table of text encodings.

static
TextEncoding::Ptr
global(TextEncoding::Ptr encoding)

Sets global TextEncoding object.

This function sets the global encoding to the argument and returns a reference of the previous global encoding.

static
TextEncoding&
global()

Return the current global TextEncoding object.

static
TextEncodingManager&
manager()

Returns the TextEncodingManager.