Formatted output

From:

keith@bytebrothers.co.uk

Newsgroups:

comp.lang.c++

Date:

Thu, 26 Jul 2007 07:03:13 -0700

Message-ID:

<1185458593.347083.253240@l70g2000hse.googlegroups.com>

I've been beating my head against this for a little while, so perhaps
someone can help me out here? The code below should output exactly as
follows (the hex data lines up in a fixed font):

DATA 0123456789abcdef0123456789abcdef
    0123456789abcdef0123456789abcdef

and the code does indeed do that when I use the fprintf() call. When
I comment that line out and use the iostream line, I get gibberish. I
guess I'm just not 'getting' C++ formatted I/O yet.

Here's the code, for what it's worth:

#include <cstdio>
#include <iostream>
#include <iomanip>

static void
output(const std::string& s, unsigned char* buf, const size_t len)
{
    std::cerr << s << ' ';
    for (unsigned int i = 0; i < len; ++i)
    {
        int j = (i+1) % 16;
// std::cerr << std::setw(2) << std::ios::hex << buf[i]; // no good
        fprintf(stderr, "%02x", buf[i]); // works fine
        if ((i+1) < len && j == 0)
            std::cerr << '\n' << std::setw(s.size()) << ' ';
    }
    std::cerr << '\n';
}

int main()
{ unsigned char data[] =
        {0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef,
         0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef,
         0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef,
         0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef};

    output("DATA", data, 32);
    exit(0);
}