C ++: get the number of characters printed when using a stream

Question

Function C fprintf()returns the number of characters printed. Is there any similar functionality in C ++ when writing to a file with ofstream? I'm interested in a C ++ 03 compatible solution, if possible.

For instance:

ofstream file("outputFile");
file << "hello";

// Here would I like to know that five characters were printed.

file << " world";

// Here I would like to know that six characters were printed.

Answer 1

What you are looking for tellp().

You can use it like this:

ofstream file("outputFile");

auto pos1 = file.tellp();
file << "hello";
auto pos2 = file.tellp();
std::cout << pos2 - pos1 << std::endl;

Answer 2

"" ( , ). , , :

class countbuf: public std::streambuf {
    std::streambuf* sbuf;
    std::size_t     count;
    char            buffer[256];
    int overflow(int c) {
        if (c != std::char_traits<char>::eof()) {
            *this->pptr() = c;
            this->pbump(1);
        }
        return this->sync() == -1
            ? std::char_traits<char>::eof()
            : std::char_traits<char>::not_eof(c);
    }
    int sync() {
        std::size_t size(this->pptr() - this->pbase());
        this->count += size;
        this->setp(this->buffer, this->buffer + 256);
        return size == this->sbuf->sputn(this->pbase(), this->pptr() - this->pbase())
             ? this->sbuf->pubsync(): -1;
    }
public:
    countbuf(std::streambuf* sbuf): sbuf(sbuf), count() {
        this->setp(buffer, buffer + 256);
    }
    std::size_t count() const { return count + this->pptr() - this->pbase(); }
    std::size_t reset() const {
        std::size_t rc(this->count());
        this->sync();
        this->count = 0;
        return rc;
    }
};

, std::ostream (, , ):

countbuf     sbuf(std::cout.rdbuf()); // can't seek on this stream anyway...
std::ostream out(&sbuf);
out << "hello!\n" << std::flush;
std::cout << "count=" << out.reset() << '\n';