wstring to const wchar* using c_str()

Question

I'm trying to convert a wstring to const wchar*, but the null terminations aren't working as I expect:

index 4

index 5

code

Is there any way to convert wstring to const wchar* in the manner that I'm trying?

possible duplicate of [I want to convert std::string into a const wchar\_t \*](http://stackoverflow.com/questions/246806/i-want-to-convert-stdstring-into-a-const-wchar-t) — 101010, May 14 '14 at 21:53
@Beed, `c_str()` returns `const wchar_t *`. It's stored into a `const wchar_t *`. Why would a `const_cast` help? — chris, May 14 '14 at 21:55
I don't see the problem here? The type of your pointer is `const wchar_t*`, the debugger advances by *2* bytes on pointer increment. Which means the `+5` case is past the null character — indeterminately sequenced, May 14 '14 at 21:56
The stuff stored at `works + 5` is something you promised never to look at when you used the language. Same with `doesntWork + 5`. Don't be surprised when you implicitly say you won't look there and then look there and don't get what you expect. — chris, May 14 '14 at 21:59
What problems are you experiencing? Because the statements are OK. In which context `doesntWork` doesn't work? — 101010, May 14 '14 at 21:59
I look into my crystal ball and I saw that you're using `std::cout` instead of `std::wcout` to print `doesntwork`. — 101010, May 14 '14 at 22:04
@40two That is the code that I'm currently using, but it isn't solving my problem. — user2002287, May 14 '14 at 22:04
@40two I'm not using any form of cout, I'm passing the strings into client code. When I use the doesntWork it throws an exception, saying the string formatting is incorrect. work has a null terminator which inhabits +4 and +5, doesntWork's null terminator only inhabits +4 (i think?) I've been working on this ALL day. I believe it has something to do with "works" bring a wide string, and "doesntWork" not having a wide null terminator? — user2002287, May 14 '14 at 22:08
@user2002287, `works`'s null terminator is just `works[4]`. Each element is one `wchar_t`. The null is `sizeof(wchar_t)` zeroed bytes in that case. — chris, May 14 '14 at 22:08
@40two I'm passing both strings into the same function. works works. doesntWork throws a wrong string formatting exception — user2002287, May 14 '14 at 22:09
@user2002287 are you passing to a function that expects a BSTR ? — M.M, May 14 '14 at 22:10
@user2002287 bear in mind that the result of `c_str()` is only valid until the next time you call a non-const member function of the string, or the string is destroyed — M.M, May 14 '14 at 22:10
@user2002287 Then your client code is engaging in undefined behavior ( something like 40two's `cout< — indeterminately sequenced, May 14 '14 at 22:13

score 3 · Answer 1 · answered May 14 '14 at 22:04

Both works[5] and doesntWork[5] cause undefined behavior. The buffers are only valid up to [4], and [5] is outside that.

const wchar_t *works = L"Test";

works[0] -> L'T'
works[1] -> L'e'
works[2] -> L's'
works[3] -> L't'
works[4] -> L'\0'
works[5] -> undefined behavior, the program is broken if it ever tries to access this

wstring to const wchar* using c_str()

1 Answers1