so the following converts big endians to little ones

uint32_t ntoh32(uint32_t v)
{
    return (v << 24)
        | ((v & 0x0000ff00) << 8)
        | ((v & 0x00ff0000) >> 8)
        | (v >> 24);
}

works. like a charm.

I read 4 bytes from a big endian file into char v[4] and pass it into the above function as

 ntoh32 (* reinterpret_cast<uint32_t *> (v))

that doesn't work - because my compiler (VS 2005) automatically converts the big endian char[4] into a little endian uint32_t when I do the cast.

AFAIK, this automatic conversion will not be portable, so I use

uint32_t ntoh_4b(char v[])
{
    uint32_t a = 0;
    a |= (unsigned char)v[0];
    a <<= 8;
    a |= (unsigned char)v[1];
    a <<= 8;
    a |= (unsigned char)v[2];
    a <<= 8;
    a |= (unsigned char)v[3];
    return a;
}

yes the (unsigned char) is necessary. yes it is dog slow.

there must be a better way. anyone ?