How to Convert int to BSTR?

Question

I have a question how can BSTR accepts a number the second line here gives an error

    unsigned int number =10;
    BSTR mybstr=SysAllocString(number);

also this line gives an error

VarBstrCat(mybstr, number, &mybstr);

Thank you :) your help will be greatly appreciated :)

Well, what does the error say? Also, see the documentation for *what* the argument accepted is really used for: [`SysAllocString(number)`](http://msdn.microsoft.com/en-us/library/windows/desktop/ms221458(v=vs.85).aspx) is most definitely *wrong* and should have raised a warning or two. — user2864740, Sep 11 '14 at 22:53
here is the error cannot convert parameter 1 from 'std::wstring' to 'const OLECHAR *' — Rehab Reda, Sep 11 '14 at 22:56
Thank you MicroVirus so much :) but if I have integer and I need it to be converted to BSTR how can i do this ? — Rehab Reda, Sep 11 '14 at 23:04

score 3 · Answer 1 · edited May 23 '17 at 12:01

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First, SysAllocString accepts const OLECHAR*, not int

Second, VarBstrCat's second parameter is BSTR, not again int

To convert int to BSTR, you can do for example like this:

std::wstring s = std::to_wstring(number); // needs C++11
BSTR mybstr = SysAllocString(s.c_str());

UPDATE: Or a bit more efficient, as suggested by Remy Lebeau in comments:

BSTR mybstr = SysAllocStringLen(s.c_str(), s.length());

UPDATE2: If your compiler doesn't support C++11, you can use C function swprintf():

wchar_t buf[20];
int len = swprintf(buf, 20, L"%d", number);
BSTR mybstr = SysAllocStringLen(buf, len);

edited May 23 '17 at 12:01

Community

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answered Sep 11 '14 at 22:59

Anton Savin

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Thank you Anton :) but can u give me a suggestion how to convert int to BSTR ? :) – Rehab Reda Sep 11 '14 at 23:02
Since `wstring` knows its own length, I would suggest using `SysAllocStringLen()` instead: `BSTR mybstr = SysAllocStringLen(s.c_str(), s.length());` – Remy Lebeau Sep 11 '14 at 23:09
Thank you Anton but it seems that it is not working with me Error 'to_wstring' : is not a member of 'std' – Rehab Reda Sep 11 '14 at 23:13
@RehabReda It's a C++11 function, either enable it by `-std=c++11` or use for example `swprintf` – Anton Savin Sep 11 '14 at 23:27

Adam · Accepted Answer · 2014-09-15T23:51:04.190

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You need to convert the number to a unicode string before you can get a BSTR of it. For this you can use _itow which converts an int into a unicode string.

unsigned int number = 10;
wchar_t temp_str[11]; // we assume that the maximal string length can be 10
_itow(number, temp_str, 10);
BSTR mybstr = SysAllocString(temp_str);

edited Sep 15 '14 at 23:51

answered Sep 11 '14 at 23:06

Adam

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How to Convert int to BSTR?

2 Answers2