Encode and decode UTF-8, UTF-16 and UTF-32 strings.
UTF character support is restricted to '\u0000' <= character <= '\U0010FFFF'.
| Category | Functions |
|---|---|
| Decode | decode decodeFront |
| Lazy decode | byCodeUnit byChar byWchar byDchar byUTF |
| Encode | encode toUTF8 toUTF16 toUTF32 toUTFz toUTF16z |
| Length | codeLength count stride strideBack |
| Index | toUCSindex toUTFindex |
| Validation | isValidDchar validate |
| Miscellaneous | replacementDchar UseReplacementDchar UTFException |
Exception thrown on errors in std.utf functions.
Check whether the given Unicode code point is valid.
dchar c
| code point to check |
true iff c is a valid Unicode code point '\uFFFE' and '\uFFFF' are considered valid by isValidDchar, as they are permitted for internal use by an application, but they are not allowed for interchange by the Unicode standard.Calculate the length of the UTF sequence starting at index in str.
S str
| input range of UTF code units. Must be random access if index is passed |
size_t index
| starting index of UTF sequence (default: 0) |
UTFException if str[index] is not the start of a valid UTF sequence. stride will only analyze the first str[index] element. It will not fully verify the validity of the UTF sequence, nor even verify the presence of the sequence: it will not actually guarantee that index + stride(str, index) <= str.length.Calculate the length of the UTF sequence ending one code unit before index in str.
S str
| bidirectional range of UTF code units. Must be random access if index is passed |
size_t index
|
index one past end of UTF sequence (default: str.length) |
UTFException if str[index] is not one past the end of a valid UTF sequence. strideBack will only analyze the element at str[index - 1] element. It will not fully verify the validity of the UTF sequence, nor even verify the presence of the sequence: it will not actually guarantee that strideBack(str, index) <= index.Given index into str and assuming that index is at the start of a UTF sequence, toUCSindex determines the number of UCS characters up to index. So, index is the index of a code unit at the beginning of a code point, and the return value is how many code points into the string that that code point is.
writeln(toUCSindex(`hello world`, 7)); // 7 writeln(toUCSindex(`hello world`w, 7)); // 7 writeln(toUCSindex(`hello world`d, 7)); // 7 writeln(toUCSindex(`Ma Chérie`, 7)); // 6 writeln(toUCSindex(`Ma Chérie`w, 7)); // 7 writeln(toUCSindex(`Ma Chérie`d, 7)); // 7 writeln(toUCSindex(`さいごの果実 / ミツバチと科学者`, 9)); // 3 writeln(toUCSindex(`さいごの果実 / ミツバチと科学者`w, 9)); // 9 writeln(toUCSindex(`さいごの果実 / ミツバチと科学者`d, 9)); // 9
Given a UCS index n into str, returns the UTF index. So, n is how many code points into the string the code point is, and the array index of the code unit is returned.
writeln(toUTFindex(`hello world`, 7)); // 7 writeln(toUTFindex(`hello world`w, 7)); // 7 writeln(toUTFindex(`hello world`d, 7)); // 7 writeln(toUTFindex(`Ma Chérie`, 6)); // 7 writeln(toUTFindex(`Ma Chérie`w, 7)); // 7 writeln(toUTFindex(`Ma Chérie`d, 7)); // 7 writeln(toUTFindex(`さいごの果実 / ミツバチと科学者`, 3)); // 9 writeln(toUTFindex(`さいごの果実 / ミツバチと科学者`w, 9)); // 9 writeln(toUTFindex(`さいごの果実 / ミツバチと科学者`d, 9)); // 9
Whether or not to replace invalid UTF with replacementDchar
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.
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 |
S str
| input string or indexable Range |
size_t index
| starting index into s[]; incremented by number of code units processed |
UTFException if str[index] is not the start of a valid UTF sequence and useReplacementDchar is No.useReplacementDchar
decodeFront is a variant of decode which specifically decodes the first code point. Unlike decode, decodeFront accepts any input range of code units (rather than just a string or random access range). It also takes the range by ref and pops off the elements as it decodes them. If numCodeUnits is passed in, it gets set to the number of code units which were in the code point which was decoded.
| useReplacementDchar | if invalid UTF, return replacementDchar rather than throwing |
S str
| input string or indexable Range |
size_t numCodeUnits
| set to number of code units processed |
UTFException if str.front is not the start of a valid UTF sequence. If an exception is thrown, then there is no guarantee as to the number of code units which were popped off, as it depends on the type of range being used and how many code units had to be popped off before the code point was determined to be invalid.decodeBack is a variant of decode which specifically decodes the last code point. Unlike decode, decodeBack accepts any bidirectional range of code units (rather than just a string or random access range). It also takes the range by ref and pops off the elements as it decodes them. If numCodeUnits is passed in, it gets set to the number of code units which were in the code point which was decoded.
| useReplacementDchar | if invalid UTF, return replacementDchar rather than throwing |
S str
| input string or bidirectional Range |
size_t numCodeUnits
| gives the number of code units processed |
UTFException if str.back is not the end of a valid UTF sequence. If an exception is thrown, the str itself remains unchanged, but there is no guarantee as to the value of numCodeUnits (when passed).Encodes c into the static array, buf, and returns the actual length of the encoded character (a number between 1 and 4 for char[4] buffers and a number between 1 and 2 for wchar[2] buffers).
UTFException if c is not a valid UTF code point.Encodes c in str's encoding and appends it to str.
UTFException if c is not a valid UTF code point.Returns the number of code units that are required to encode the code point c when C is the character type used to encode it.
writeln(codeLength!char('a')); // 1
writeln(codeLength!wchar('a')); // 1
writeln(codeLength!dchar('a')); // 1
writeln(codeLength!char('\U0010FFFF')); // 4
writeln(codeLength!wchar('\U0010FFFF')); // 2
writeln(codeLength!dchar('\U0010FFFF')); // 1
Returns the number of code units that are required to encode str in a string whose character type is C. This is particularly useful when slicing one string with the length of another and the two string types use different character types.
| C | the character type to get the encoding length for |
InputRange input
| the input range to calculate the encoding length from |
input when encoded to C
import std.conv : to;
assert(codeLength!char("hello world") ==
to!string("hello world").length);
assert(codeLength!wchar("hello world") ==
to!wstring("hello world").length);
assert(codeLength!dchar("hello world") ==
to!dstring("hello world").length);
assert(codeLength!char(`プログラミング`) ==
to!string(`プログラミング`).length);
assert(codeLength!wchar(`プログラミング`) ==
to!wstring(`プログラミング`).length);
assert(codeLength!dchar(`プログラミング`) ==
to!dstring(`プログラミング`).length);
string haystack = `Être sans la verité, ça, ce ne serait pas bien.`;
wstring needle = `Être sans la verité`;
assert(haystack[codeLength!char(needle) .. $] ==
`, ça, ce ne serait pas bien.`);
Checks to see if str is well-formed unicode or not.
UTFException if str is not well-formed.Encodes the elements of s to UTF-8 and returns a newly allocated string of the elements.
S s
| the string to encode |
byUTF.import std.algorithm.comparison : equal;
// The ö is represented by two UTF-8 code units
assert("Hellø"w.toUTF8.equal(['H', 'e', 'l', 'l', 0xC3, 0xB8]));
// 𐐷 is four code units in UTF-8
assert("𐐷"d.toUTF8.equal([0xF0, 0x90, 0x90, 0xB7]));
Encodes the elements of s to UTF-16 and returns a newly GC allocated wstring of the elements.
S s
| the range to encode |
byUTF.import std.algorithm.comparison : equal;
// these graphemes are two code units in UTF-16 and one in UTF-32
writeln("𤭢"d.length); // 1
writeln("𐐷"d.length); // 1
assert("𤭢"d.toUTF16.equal([0xD852, 0xDF62]));
assert("𐐷"d.toUTF16.equal([0xD801, 0xDC37]));
Encodes the elements of s to UTF-32 and returns a newly GC allocated dstring of the elements.
S s
| the range to encode |
byUTF.Returns a C-style zero-terminated string equivalent to str. str must not contain embedded '\0''s as any C function will treat the first '\0' that it sees as the end of the string. If str.empty is true, then a string containing only '\0' is returned.
toUTFz accepts any type of string and is templated on the type of character pointer that you wish to convert to. It will avoid allocating a new string if it can, but there's a decent chance that it will end up having to allocate a new string - particularly when dealing with character types other than char.
Warning 1: If the result of toUTFz equals str.ptr, then if anything alters the character one past the end of str (which is the '\0' character terminating the string), then the string won't be zero-terminated anymore. The most likely scenarios for that are if you append to str and no reallocation takes place or when str is a slice of a larger array, and you alter the character in the larger array which is one character past the end of str. Another case where it could occur would be if you had a mutable character array immediately after str in memory (for example, if they're member variables in a user-defined type with one declared right after the other) and that character array happened to start with '\0'. Such scenarios will never occur if you immediately use the zero-terminated string after calling toUTFz and the C function using it doesn't keep a reference to it. Also, they are unlikely to occur even if you save the zero-terminated string (the cases above would be among the few examples of where it could happen). However, if you save the zero-terminate string and want to be absolutely certain that the string stays zero-terminated, then simply append a '\0' to the string and use its ptr property rather than calling toUTFz.
Warning 2: When passing a character pointer to a C function, and the C function keeps it around for any reason, make sure that you keep a reference to it in your D code. Otherwise, it may go away during a garbage collection cycle and cause a nasty bug when the C code tries to use it.
auto p1 = toUTFz!(char*)("hello world");
auto p2 = toUTFz!(const(char)*)("hello world");
auto p3 = toUTFz!(immutable(char)*)("hello world");
auto p4 = toUTFz!(char*)("hello world"d);
auto p5 = toUTFz!(const(wchar)*)("hello world");
auto p6 = toUTFz!(immutable(dchar)*)("hello world"w);
toUTF16z is a convenience function for toUTFz!(const(wchar)*).
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.
Returns the total number of code points encoded in str.
toUCSindex. UTFException if str is not well-formed.Inserted in place of invalid UTF sequences.
Iterate a range of char, wchar, or dchars by code unit.
The purpose is to bypass the special case decoding that std.range.primitives.front does to character arrays. As a result, using ranges with byCodeUnit can be nothrow while std.range.primitives.front throws when it encounters invalid Unicode sequences.
A code unit is a building block of the UTF encodings. Generally, an individual code unit does not represent what's perceived as a full character (a.k.a. a grapheme cluster in Unicode terminology). Many characters are encoded with multiple code units. For example, the UTF-8 code units for ø are 0xC3 0xB8. That means, an individual element of byCodeUnit often does not form a character on its own. Attempting to treat it as one while iterating over the resulting range will give nonsensical results.
R r
| an input range of characters (including strings) or a type that implicitly converts to a string type. |
r is not an auto-decodable string (i.e. a narrow string or a user-defined type that implicits converts to a string type), then r is returned. Otherwise, r is converted to its corresponding string type (if it's not already a string) and wrapped in a random-access range where the element encoding type of the string (its code unit) is the element type of the range, and that range returned. The range has slicing. If r is quirky enough to be a struct or class which is an input range of characters on its own (i.e. it has the input range API as member functions), and it's implicitly convertible to a string type, then r is returned, and no implicit conversion takes place. std.uni docs for a reference on Unicode terminology. For a range that iterates by grapheme cluster (written character) see std.uni.byGrapheme.import std.range.primitives; auto r = "Hello, World!".byCodeUnit(); static assert(hasLength!(typeof(r))); static assert(hasSlicing!(typeof(r))); static assert(isRandomAccessRange!(typeof(r))); static assert(is(ElementType!(typeof(r)) == immutable char)); // contrast with the range capabilities of standard strings auto s = "Hello, World!"; static assert(isBidirectionalRange!(typeof(r))); static assert(is(ElementType!(typeof(s)) == dchar)); static assert(!isRandomAccessRange!(typeof(s))); static assert(!hasSlicing!(typeof(s))); static assert(!hasLength!(typeof(s)));
byCodeUnit does no Unicode decoding string noel1 = "noe\u0308l"; // noël using e + combining diaeresis assert(noel1.byCodeUnit[2] != 'ë'); writeln(noel1.byCodeUnit[2]); // 'e' string noel2 = "no\u00EBl"; // noël using a precomposed ë character // Because string is UTF-8, the code unit at index 2 is just // the first of a sequence that encodes 'ë' assert(noel2.byCodeUnit[2] != 'ë');
Iterate an input range of characters by char, wchar, or dchar. These aliases simply forward to byUTF with the corresponding C argument.
| R r | input range of characters, or array of characters |
Iterate an input range of characters by char type C by encoding the elements of the range.
UTF sequences that cannot be converted to the specified encoding are replaced by U+FFFD per "5.22 Best Practice for U+FFFD Substitution" of the Unicode Standard 6.2. Hence byUTF is not symmetric. This algorithm is lazy, and does not allocate memory. @nogc, pure-ity, nothrow, and @safe-ty are inferred from the r parameter.
| C |
char, wchar, or dchar
|
R is a range and not auto-decodable, as defined by std.traits.isAutodecodableString, and if the base range is also a forward range. Or, if R is a range and it is auto-decodable and is(ElementEncodingType!typeof(r) == C), then the range is passed to byCodeUnit. Otherwise, an input range of characters.import std.algorithm.comparison : equal; // hellö as a range of `char`s, which are UTF-8 "hell\u00F6".byUTF!char().equal(['h', 'e', 'l', 'l', 0xC3, 0xB6]); // `wchar`s are able to hold the ö in a single element (UTF-16 code unit) "hell\u00F6".byUTF!wchar().equal(['h', 'e', 'l', 'l', 'ö']); // 𐐷 is four code units in UTF-8, two in UTF-16, and one in UTF-32 "𐐷".byUTF!char().equal([0xF0, 0x90, 0x90, 0xB7]); "𐐷".byUTF!wchar().equal([0xD801, 0xDC37]); "𐐷".byUTF!dchar().equal([0x00010437]);
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