ostream base flags with custom numeric class

[monarch_dodra]

I'm writing a custom numeric class, "BigInt" which I want to integrate with any standard ostream.

While I want this to work

std::cout << aBigInt << std::endl;

I also want this to work:

While I want this to work

std::cout << std::hex << aBigInt << std::endl;
std::cout << std::dec << aBigInt << std::endl;
std::cout << std::oct << aBigInt << std::endl;

So far, I am able to do this: (simplified removed lots of else, checks)

std::ostream& BigInt::tostream (std::ostream& ioOut)
{
    std::ios_base::fmtflags ff(ioOut.flags());
    if (ff & std::ios_base::hex) ioOut << getHexString();
    if (ff & std::ios_base::dec) ioOut << getDecString();
    if (ff & std::ios_base::oct) ioOut << getOctString();
    return ioOut;
}

This all works pretty nice, but I am having trouble with "std::showbase" and "std::internal". (as in "0x000000a7" instead of "a7")
Because what I am returning to the stream is actually an std::string, I have to emulate their behavior by hand, by hand-inserting the base, then inserting in between the internal padding, the inserting the string into the stream. I gives me something like this:

    std::ios_base::fmtflags baseFlags(ioOut.flags());

    std::stringstream aSsBase;
    std::stringstream aSsNumber;
    
    if ( baseFlags & std::ios_base::showbase ) aSsBase << "0x";
    
    aSsNumber << getHexString(); //See above code, compacted here

    if ( baseFlags & std::ios_base::internal )
    {
        aSsBase << std::setfill(ioOut.fill());
        aSsBase << std::setw(ioOut.width() - aSsBase.str().size() );
        aSsBase << std::right;
    }
    aSsBase << aSsNumber.str();
    ioOut << aSsBase.str();
}

So anyways, that's how I do it. Is there a way to avoid all the above? Not only is it a bit hackish, I'm not even sure all platforms use "0x" and "0" as base prefix, and overall, doesn't look very portable. Finally, there are probably a bunch of flags I am miss-handling/forgetting.

Would it be possible to insert a string into the stream, but somehow tell the stream it should treat it as a number, and let it take care of the rest (padding, base etc)?