Streaming byte arrays

[Chris87]

I've been looking for a way to effectively extract variables from data stored in a byte array. I looked at std:stream but the only examples I see used are with the cout object. There seems to be no way to set the underlying source to an array of bytes.

Right now my code looks like this, and I can imagine it looks rather ugly:

char *p = data+9; // start at byte 10
char str31[31];
user->SetName(std::memmove(str31, p, 31)); p += 31;
char i = *(p++);
user->SetPassword(std::memmove(str31, p, 31), i); p += 31;
user->SetAux(*(std::uint32_t*)p); p += 24; // skip 24 bytes of unused junk
user->SetRoom(*(std::uint32_t*)p); // skip rest

[laserlight]

There seems to be no way to set the underlying source to an array of bytes.

Perhaps you could use a stringstream, though I am not sure how well that would play with binary content.

[Yarin]

There seems to be no way to set the underlying source to an array of bytes.

Not quite sure what you're after, but, there is actually a clear way:

struct underlying_source
{
    char muh_data[33];
    int moar_data;
};

auto p = static_cast<const underlying_source*>(data + 9); // start at byte 10, it's how i roll, dawg
user->SetName(p->muh_data);

[Chris87]

Hmm... I reordered the fields to reduce memory footprint, however.

[Elysia]

Hmm... I reordered the fields to reduce memory footprint, however.

I don't know what you mean by that.
Regardless, I would think Yarin's idea is a good one. std::string also has a constructor that takes two iterators for [begin, end), allowing you to construct a string from a sequence of bytes.
Otherwise I'd propose a helper function/object, something along the lines of (won't work for strings, though):

template<typename T>
T func(int& pos, unsigned char* data)
{
    auto newdata = *reinterpret_cast<T*>(&data[pos]);
    pos += sizeof(T);
    return newdata;
}

stringstreams may also work (as laserlight mentions(. I haven't tested them with raw data, though.

[Chris87]

stringstream does seem to work for me. I just tried it out. I did do a test with it some time ago. I guess I either remember it wrong or did something silly like stream << &someInt;