Converting unicode strings and vice-versa

Question

I'm kind of new to using Unicode string and pointers and I've no idea how the conversion to unicode to ascii and versa-versa works. Following is what I'm trying to do,

const wchar_t *p = L"This is a string";

If I wanted to convert it to char*, how would the conversion work with converting wchar_t* to char* and vice-versa?

or by value using wstring to string class object and vice-versa

std::wstring wstr = L"This is a string";

If i'm correct, can you just copy the string to a new buffer without conversion?

Answer 1

In the future (VS 2010 already supports it), this will be possible in standard C++ (finally!):

#include <string>
#include <locale>

std::wstring_convert<std::codecvt_utf8<wchar_t>> converter;
const std::wstring wide_string = L"This is a string";
const std::string utf8_string = converter.to_bytes(wide_string);

Answer 2

The conversion from ASCII to Unicode and vice versa are quite trivial. By design, the first 128 Unicode values are the same as ASCII (in fact, the first 256 are equal to ISO-8859-1).

So the following code works on systems where char is ASCII and wchar_t is Unicode:

const char* ASCII = "Hello, world";
std::wstring Unicode(ASCII, ASCII+strlen(ASCII));

You can't reverse it this simple: 汉 does exist in Unicode but not in ASCII, so how would you "convert" it?