Convert std::wstring to WCHAR*

Question

I have no idea how to convert a std::wstring to a WCHAR*

std::wstring wstrProcToSearch;
WCHAR * wpProcToSearch = NULL;

std::wcin >> wstrProcToSearch;  // input std::wstring
// now i need to convert the wstring to a WCHAR*

Does anyone know how to accomplish this?

Answer 1

If you want to convert from std::wstring to const WCHAR* (ie the returned pointer gives read-only access to the string content), then calling std::wstring::c_str() method is just fine:

std::wstring wstrProcToSearch;
std::wcin >> wstrProcToSearch;  // input std::wstring

// Convert to const WCHAR* (read-only access)
const WCHAR * wpszProcToSearch = wstrProcToSearch.c_str();

Instead, if you want to modify std::wstring 's content, things are different. You can use &wstr[0] (where wstr is a non-empty instance of std::wstring ) to access the content of the std::wstring (starting from the address of its first characters, and noting that characters are stored contiguously in memory), but you must pay attention to not overrun string's pre-allocated memory.

In general, if you have a std::wstring of length L , you can access characters from index 0 to (L-1) .
Overwriting the terminating '\\0' (located at index L ) is undefined behavior (in practice, it's OK on Visual C++, at least with VC9/VS2008 and VC10/VS2010).

If the string has not the proper size (ie it's not big enough for your needs), then you can call std::wstring::resize() to make room for new characters (ie resizing internal std::wstring 's buffer), and then use &wstr[0] to read-write std::wstring 's content.

Answer 2

If the string is already the proper length and will not need to be changed, you can get a non-const pointer by taking a pointer to the first character:

WCHAR * wpProcToSearch = &wstrProcToSearch[0];

This is guaranteed to work in C++11 and there are no known implementations of C++03 where it doesn't.

If you only need a const pointer you should use c_str :

const WCHAR * wpProcToSearch = wstrProcToSearch.c_str();

Answer 3

I think you can use

wpProcToSearch = wstrProcToSearch.c_str()

like you do with a normal std::string.

Answer 4

I recommend this approach:

wstring str = L"Hallo  x     y   111 2222  3333 rrr 4444   ";
wchar_t* psStr = &str[0];

It is quite simple but you can not change the length of the string at all. So moving "\\0" might not be valid...