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Function std.utf.decode

Decodes and returns the code point starting at str[index]. index is advanced to one past the decoded code point. If the code point is not well-formed, then a UTFException is thrown and index remains unchanged.

dchar decode(Flag!("useReplacementDchar") useReplacementDchar = No.useReplacementDchar, S) (
  auto ref S str,
  ref size_t index
if (!isSomeString!S && isRandomAccessRange!S && hasSlicing!S && hasLength!S && isSomeChar!(ElementType!S));

dchar decode(Flag!("useReplacementDchar") useReplacementDchar = No.useReplacementDchar, S) (
  auto scope ref S str,
  ref size_t index
) pure @trusted
if (isSomeString!S);

decode will only work with strings and random access ranges of code units with length and slicing, whereas decodeFront will work with any input range of code units.


useReplacementDchar if invalid UTF, return replacementDchar rather than throwing
str input string or indexable Range
index starting index into s[]; incremented by number of code units processed


decoded character


UTFException if str[index] is not the start of a valid UTF sequence and useReplacementDchar is No.useReplacementDchar


size_t i;

assert("a".decode(i) == 'a' && i == 1);
i = 0;
assert("å".decode(i) == 'å' && i == 2);
i = 1;
assert("aå".decode(i) == 'å' && i == 3);
i = 0;
assert("å"w.decode(i) == 'å' && i == 1);

// ë as a multi-code point grapheme
i = 0;
assert("e\u0308".decode(i) == 'e' && i == 1);
// ë as a single code point grapheme
i = 0;
assert("ë".decode(i) == 'ë' && i == 2);
i = 0;
assert("ë"w.decode(i) == 'ë' && i == 1);


Walter Bright and Jonathan M Davis


Boost License 1.0.