std::stringstream and std::ios::binary

Question

I want to write to a std::stringstream without any transformation of, say line endings.

I have the following code:

void decrypt(std::istream& input, std::ostream& output)
{
    while (input.good())
    {
        char c = input.get()
        c ^= mask;
        output.put(c);

        if (output.bad())
        {
            throw std::runtime_error("Output to stream failed.");
        }
    }
}

The following code works like a charm:

std::ifstream input("foo.enc", std::ios::binary);
std::ofstream output("foo.txt", std::ios::binary);
decrypt(input, output);

If I use a the following code, I run into the std::runtime_error where output is in error state.

std::ifstream input("foo.enc", std::ios::binary);
std::stringstream output(std::ios::binary);
decrypt(input, output);

If I remove the std::ios::binary the decrypt function completes without error, but I end up with CR,CR,LF as line endings.

I am using VS2008 and have not yet tested the code on gcc. Is this the way it supposed to behave or is MS's implementation of std::stringstream broken?

Any ideas how I can get the contents into a std::stringstream in the proper format? I tried putting the contents into a std::string and then using write() and it also had the same result.

Answer 1

AFAIK, the binary flag only applies to fstream , and stringstream never does linefeed conversion, so it is at most useless here.

Moreover, the flags passed to stringstream 's ctor should contain in , out or both. In your case, out is necessary (or better yet, use an ostringstream ) otherwise, the stream is in not in output mode, which is why writing to it fails.

stringstream ctor's "mode" parameter has a default value of in|out , which explains why things are working properly when you don't pass any argument.

Answer 2

尝试使用

std::stringstream output(std::stringstream::out|std::stringstream::binary);