Is there any difference between these two string storage formats?
- 1there's a pretty good answer to this question here: stackoverflow.com/questions/402283/stdwstring-vs-stdstring/…Idan K– Idan K2010-11-22 15:49:34 +00:00Commented Nov 22, 2010 at 15:49
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3 Answers
std::wstring is a container of wchar_t. The size of wchar_t is not specified—Windows compilers tend to use a 16-bit type, Unix compilers a 32-bit type.
UTF-16 is a way of encoding sequences of Unicode code points in sequences of 16-bit integers.
Using Visual Studio, if you use wide character literals (e.g. L"Hello World") that contain no characters outside of the BMP, you'll end up with UTF-16, but mostly the two concepts are unrelated. If you use characters outside the BMP, std::wstring will not translate surrogate pairs into Unicode code points for you, even if wchar_t is 16 bits.
4 Comments
hkBattousai
Do you mean that std::wstring is the same with UTF-16 for only the non-BMP unicode character when used in Windows operating system?
JoeG
No. std::wstring is just a container of integers. The encoding of the container depends entirely on the data you insert into the container.
Loki Astari
+1: For people unfamiliar with UTF it may be wise to define BMP.
hkBattousai
Your last paragraph is the answer to my question. Thank you.
UTF-16 is a specific Unicode encoding. std::wstring is a string implementation that uses wchar_t as its underlying type for storing each character. (In contrast, regular std::string uses char).
The encoding used with wchar_t does not necessarily have to be UTF-16—it could also be UTF-32 for example.
1 Comment
greyfade
It could also be UCS-2 or S-JIS or Big 5 or ... well, anything.
UTF-16 is a concept of text represented in 16-bit elements but an actual textual character may consist of more than one element
std::wstring is just a collection of these elements, and is a class primarily concerned with their storage.
The elements in a wstring, wchar_t is at least 16-bits but could be 32 bits.
4 Comments
hkBattousai
Can you please explain in more detail, like giving an example. For instance the character 'A' is stored in std::wstring like "0x0041". How is it stored in UTF-16 format?
Inverse
16-byte ?? woah that's a hardcore character encoding
Matthieu M.
@Inverse: That's why everyone should just use ASCII, there wouldn't be so much grief on memory use ;)
DavidRR
For those who may not understand the humor in the above comments, UTF-16 is a 16-bit Unicode encoding. Also, in UTF-16, a character that is defined using more than one 16-bit element is done so via surrogate pairs.