How can I discover/control the level of internal buffering in a C++ fstream?

Question

Say I do this (a contrived example):

#include <iostream>
#include <fstream>

using namespace std;

int main(int argc, char* argv[])
{
    ifstream ifs(argv[1]);

    char ch;
    while(ifs.read(&ch, 1)) {
        cout << ch;
    }
}

I assume(hope) that the iostream library does some internal buffering here and doesn't turn this into gazillions of one-byte file-read operations at the OS level.

Is there a way of:

a) Finding out the size of ifstream's internal buffer?

b) Changing the size of ifstream's internal buffer?

I'm writing a file filter that needs to read multi-gigabyte files in small chunks and I'd like to experiment with different buffer sizes to see if it affects performance.