How does std::stringstream handle wchar_t* in operator<

Question

Given that the following snippet doesn't compile:

std::stringstream ss;
ss << std::wstring(L"abc");

I didn't think this one would, either:

std::stringstream ss;
ss << L"abc";

But it does (on VC++ at least). I'm guessing this is due to the following ostream::operator<< overload:

ostream& operator<< (const void* val );

Does this have the potential to silently break my code, if I inadvertently mix character types?

Are you intentionally using `stringstream` instead of `wstringstream`? — dgnorton, Oct 01 '10 at 19:54
No, it's actually the other way around. I'm using `wstringstream` all the time and sometimes forget to add `L` before the string, especially when writing log messages. — Pedro d'Aquino, Oct 04 '10 at 13:02

Steve Townsend · Answer 1 · 2010-10-01T20:03:43.540

14

Yes - you need wstringstream for wchar_t output.

You can mitigate this by not using string literals. If you try to pass const wstring& to stringstream it won't compile, as you noted.

edited Oct 01 '10 at 20:03

answered Oct 01 '10 at 19:55

Steve Townsend

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score 6 · Accepted Answer · answered Oct 01 '10 at 19:54

Does this have the potential to silently break my code, if I inadvertently mix character types?

In a word: yes, and there is no workaround that I know of. You'll just see a representation of a pointer value instead of a string of characters, so it's not a potential crash or undefined behaviour, just output that isn't what you want.

How does std::stringstream handle wchar_t* in operator<

2 Answers2