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# core.internal.utf

Encode and decode UTF-8, UTF-16 and UTF-32 strings.
For Win32 systems, the C wchar_t type is UTF-16 and corresponds to the D wchar type. For Posix systems, the C wchar_t type is UTF-32 and corresponds to the D utf.dchar type.
UTF character support is restricted to (\u0000 <= character <= \U0010FFFF).
See Also:
Wikipedia
http://www.cl.cam.ac.uk/~mgk25/unicode.html#utf-8
http://anubis.dkuug.dk/JTC1/SC2/WG2/docs/n1335
License:
Boost License 1.0.
Authors:
Walter Bright, Sean Kelly

Source core/internal/utf.d

pure nothrow @nogc @safe bool `isValidDchar`(dchar `c`);
  Test if c is a valid UTF-32 character.
  \uFFFE and \uFFFF are considered valid by this function, as they are permitted for internal use by an application, but they are not allowed for interchange by the Unicode standard.
  Returns:
  true if it is, false if not.
pure nothrow @nogc @safe uint `stride`(scope const char[] `s`, size_t `i`);
  stride() returns the length of a UTF-8 sequence starting at index i in string s.
  Returns:
  The number of bytes in the UTF-8 sequence or 0xFF meaning s[i] is not the start of of UTF-8 sequence.
pure nothrow @nogc @safe uint `stride`(scope const wchar[] `s`, size_t `i`);
  stride() returns the length of a UTF-16 sequence starting at index i in string s.
pure nothrow @nogc @safe uint `stride`(scope const dchar[] `s`, size_t `i`);
  stride() returns the length of a UTF-32 sequence starting at index i in string s.
  Returns:
  The return value will always be 1.
pure @safe size_t `toUCSindex`(scope const char[] `s`, size_t `i`);
pure @safe size_t `toUCSindex`(scope const wchar[] `s`, size_t `i`);
pure nothrow @nogc @safe size_t `toUCSindex`(scope const dchar[] `s`, size_t `i`);
  Given an index i into an array of characters s[], and assuming that index i is at the start of a UTF character, determine the number of UCS characters up to that index i.
pure @safe size_t `toUTFindex`(scope const char[] `s`, size_t `n`);
pure nothrow @nogc @safe size_t `toUTFindex`(scope const wchar[] `s`, size_t `n`);
pure nothrow @nogc @safe size_t `toUTFindex`(scope const dchar[] `s`, size_t `n`);
  Given a UCS index n into an array of characters s[], return the UTF index.
pure @safe dchar `decode`(scope const char[] `s`, ref size_t `idx`);
pure @safe dchar `decode`(scope const wchar[] `s`, ref size_t `idx`);
pure @safe dchar `decode`(scope const dchar[] `s`, ref size_t `idx`);
  Decodes and returns character starting at s[idx]. idx is advanced past the decoded character. If the character is not well formed, a UtfException is thrown and idx remains unchanged.
pure nothrow @safe void `encode`(ref char[] `s`, dchar `c`);
pure nothrow @safe void `encode`(ref wchar[] `s`, dchar `c`);
pure nothrow @safe void `encode`(ref dchar[] `s`, dchar `c`);
  Encodes character c and appends it to array s[].
pure nothrow @nogc @safe ubyte `codeLength`(C)(dchar `c`);
  Returns the code length of c in the encoding using C as a code point. The code is returned in character count, not in bytes.
pure nothrow @safe bool `isValidString`(S)(scope const S `s`);
  Checks to see if string is well formed or not. S can be an array of char, wchar, or dchar. Returns false if it is not. Use to check all untrusted input for correctness.
pure nothrow @safe string `toUTF8`(return scope string `s`);
pure @trusted string `toUTF8`(scope const wchar[] `s`);
pure @trusted string `toUTF8`(scope const dchar[] `s`);
  Encodes string s into UTF-8 and returns the encoded string.
pure @trusted wstring `toUTF16`(scope const char[] `s`);
pure @safe wptr `toUTF16z`(scope const char[] `s`);
pure nothrow @safe wstring `toUTF16`(return scope wstring `s`);
pure nothrow @trusted wstring `toUTF16`(scope const dchar[] `s`);
  Encodes string s into UTF-16 and returns the encoded string. toUTF16z() is suitable for calling the 'W' functions in the Win32 API that take an LPWSTR or LPCWSTR argument.
pure @trusted dstring `toUTF32`(scope const char[] `s`);
pure @trusted dstring `toUTF32`(scope const wchar[] `s`);
pure nothrow @safe dstring `toUTF32`(return scope dstring `s`);
  Encodes string s into UTF-32 and returns the encoded string.

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