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From: Paul Bibbings on 8 Jun 2010 14:19
LiloLilo <danilobrambilla(a)tiscali.it> writes:
>
> please try this code derived from the one you provided above. It
> produces two different files. Compiler is Visual C++ 2010
>
> // #include "stdafx.h" // removed non-standard header for GCC build
>
> #include <fstream>
>
> unsigned TotalBitCounter = 0;
>
> void WriteBitsToFile(unsigned Data,
> unsigned Length,
> std::ofstream & OutFile)
> {
> static unsigned BitBuffer = 0;
> static unsigned BitCounter = 0;
// ...
> }
>
>
> template <typename T2>
> void WriteBitsToFile(T2 Data,
> unsigned Length,
> std::ofstream & OutFile)
> {
> static unsigned BitBuffer = 0;
> static unsigned BitCounter = 0;
// ...
> }
>
>
> int main()
> {
> std::ofstream out1("Out1.txt");
> if (out1)
> {
> WriteBitsToFile(12345U, 2, out1);
> WriteBitsToFile(12345U, 5, out1);
// ...
> }
>
>
> std::ofstream out2("Out2.txt");
> if (out1) // my error!
> {
> WriteBitsToFile(12345U, 2, out2);
> WriteBitsToFile(12345U, 5, out2);
// ...
> }
> }

For this example you will see that you are not actually calling your
templated function at all, where my understanding of the original problem
lay in your wanting to claim a difference between the two as to when
writes occured (and, in particular, something to do with your static
BitBuffer being "flushed to 0" between calls for the template function).

In your code here the difference in the files arises merely because the
total number of bytes added to the buffer written to Out1.txt is not
divisible by 32 (being 102) so that the accumulation for write to
Out2.txt begins with a non-empty buffer. Is this just an error on your
part in putting together this example, or does it perhaps reflect the
nature of the problem you were having originally?

If you correct the code for your example here (abridged above), using:

std::ofstream out2("Out2.txt");
if (out2) // corrects an error in my example, duplicated in yours
{
WriteBitsToFile<>(12345U, 2, out2);
WriteBitsToFile<>(12345U, 2, out2);
// ...
}

so that the function template is instantiated and used for the second
(otherwise identical) series of invocations then I am sure you will find
- as I do, building with gcc-4.4.3 - that the two files will again be
identical.
Note: I don't have access to VS 2010, so I had to remove stdafx.h.

Regards

Paul Bibbings

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