How to pass BSTR to printf?

Question

I have a non-unicode (MBCS) C++ project building with VS2013.

Given a BSTR value, how should I pass this to printf safely?

Did you search? [This](http://stackoverflow.com/questions/13725519/how-to-convert-bstr-to-stdstring-in-visual-studio-c-2010) will get you most of the way there... — trojanfoe, Sep 09 '15 at 14:39
Possible duplicate of [Convert BSTR to char\*](http://stackoverflow.com/questions/3648848/convert-bstr-to-char). — Frédéric Hamidi, Sep 09 '15 at 14:40
Not a duplicate. `printf` can print `wchar_t` so there's no point in the conversion. — MSalters, Sep 09 '15 at 14:42
I did search and found no direct duplicate, or direct answer on other sites - which I found very surprising. I wondered if `_bstr_t` is the answer, as it so often is with BSTR? — Mr. Boy, Sep 09 '15 at 14:43

score 10 · Answer 1 · answered Sep 09 '15 at 14:44

10

A BSTR really is a WCHAR* with preceding length information. You can ignore that length part for printing purposes. So:

BSTR str = foo();
printf("%S", str); // Capital S

answered Sep 09 '15 at 14:44

MSalters

173,980
10
155
350

Can you point out the documentation for the capital S printf specifier? It doesn't appear to be standard C. – eerorika Sep 09 '15 at 14:49
@user2079303 https://msdn.microsoft.com/en-us/library/hf4y5e3w.aspx - this is MSDN so it _is_ Microsoft-specific - the link says so. – xxbbcc Sep 09 '15 at 14:56
I figured that with `BSTR` being Microsoft-specific this isn't an issue. `%ls` is portable. – MSalters Sep 09 '15 at 15:00
You can also use `wprintf()` – bobobobo Aug 13 '21 at 01:37

score 1 · Answer 2 · edited May 23 '17 at 11:53

A BSTR is a pointer to a length-prefixed (at offset -4) and 0-terminated wide-character string. You can pass it to any function that is capable of handling a 0-terminated wide-character string. (The actual string starts at offset 0.)

If the target function cannot handle wide characters, then you need to convert the string to multibyte characters (this is the case if you want to use standard printf where the S type field character is not available). This (already commented) link provides information about that: Convert BSTR to char*

@MSalters' answer has the code example (don't want to duplicate 2 trivial lines): https://stackoverflow.com/a/32482688/682404

How to pass BSTR to printf?

2 Answers2