如何跟踪写入std :: ostream对象的字节数？

Question

I want to write a bunch of data to an ostream object and return the number of bytes written. For example:

using namespace std;
size_t writeStuffToStream(ostream &stream)
{
    stream << some_string << some_integer << some_other_arbitrary_object << endl;
    return number_of_bytes_written;
}

There is the obvious workaround of writing everything to a stringstream and getting the byte count out of that, and then writing the stringstream to the stream, but that takes extra time and memory.

I also realize that if if all the data I wanted to write were preexisting strings, then there would be no problem. It's some_integer and some_other_arbitrary_object that are the problem.

Answer 1

Use the ostream tellp() method.

Note that this might fail if the provided ostream does not support positions. In that case you can create a temporary ostringstream to format your data, then extract the string , get its length and send it to the input ostream .

You can probably also write a custom ostream that send to another ostream and count emitted characters. I expected to find a virtual method to override in ostream to write just characters, but I did not find it :( You can re-use the stringstream code and replace the buffer writes to writes to an other ostream. string-stream.cc is about 500 lines long, so that's not this bad.