问题
Is there any difference between these two string storage formats?
回答1:
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.
回答2:
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.
回答3:
UTF-16 is a concept of text represented in 16-byte elements but an actual textual character may consist of one than 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.
来源：https://stackoverflow.com/questions/4247236/what-is-the-difference-between-utf-16-and-stdwstring