Question

I have 10 files need to be open for write in sequence. Can I have one fstream to do this? Do I need to do anything special (except flush()) in between each file or just call open(file1, fstream::out | std::ofstream::app) for a each file and close the stream at the end of all 10 files are written.

Answer 1

You will need to close it first, because calling open on an already open stream fails. (Which means the failbit flag is set to true). Note close() flushes, so you don’t need to worry about that:

std::ofstream file("1");
// ...
file.close();
file.clear(); // clear flags
file.open("2");
// ...

// and so on

Also note, you don’t need to close() it the last time; the destructor does that for you (and therefore also flush()‘s). This may make a nice utility function:

template <typename Stream>
void reopen(Stream& pStream, const char * pFile,
            std::ios_base::openmode pMode = ios_base::out)
{
    pStream.close();
    pStream.clear();
    pStream.open(pFile, pMode);
}

And you get:

std::ofstream file("1");
// ...
reopen(file, "2")
// ...

// and so on