Re: wcstombs n <= INT_MAX

From:

Alex Blekhman <xfkt@oohay.moc>

Newsgroups:

microsoft.public.vc.language

Date:

Wed, 06 Jun 2007 11:31:08 +0300

Message-ID:

<#6#tJUBqHHA.596@TK2MSFTNGP06.phx.gbl>

Anders Eriksson wrote:

Igor Tandetnik wrote:

Or, more likely, you are passing a negative value as buffer size, and it
wraps around (gets converted to a large unsigned integer).

Yes that's right. The call looks like this
if(wcstombs(x_szBuffer,x_wszBuffer,-1) == ((size_t)-1))

Why will it wrap around and how do I fix it?

This code is dangerous. It passes arbitrary large count of
bytes for destination buffer. Probably original assumption
was that source string is null-terminated and destination
buffer is large enough in order to accommodate for converted
string.

Both assumptions may be wrong at run time. Debug version of
CRT is smart enough to check input parameters for
`wcstombs'. That's why you see the assertion. In order to
fix the code you need to supply reasonable buffer size. For
example:

     wchar_t wsz[] = L"Hello World!";
     size_t count = wcstombs(NULL, wsz, 0);
     vector<char> sz;
     sz.resize(count + 1, 0);

     size_t ret = wcstombs(&sz.front(), wsz, count);
     assert(ret != -1);

Alex