CODEWITHSUNDEEP
c++
Datsik
Datsik

Reputation: 14824

What is the point of left shifting by 0?

I'm currently trying to implement a google authenticator for an open source server and they have this small bit of code

  if (securityFlags & 0x01)               // PIN input
                {
                    pkt << uint32(0);
                    pkt << uint64(0) << uint64(0);      // 16 bytes hash?
                    // This triggers the 2 factor authenticator entry to popup on the client side

                }

                if (securityFlags & 0x02)               // Matrix input
                {
                    pkt << uint8(0);
                    pkt << uint8(0);
                    pkt << uint8(0);
                    pkt << uint8(0);
                    pkt << uint64(0);
                }

                if (securityFlags & 0x04)               // Security token input
                {
                    pkt << uint8(1);
                }

I'm just trying to figure out why they use pkt << uint32(0), as they seem completely redundant to me. And they also use it a lot of times over, which makes even less sense.

Any ideas why their code was written like that?

Upvotes: 3

Views: 372

Answers (2)

marcinj
marcinj

Reputation: 49986

operator<< is overloaded for ByteBuffer (this is a pkt type), and it looks as follows:

https://github.com/mangostwo/server/blob/b8ce9508483375a36699c309bce36810c4548007/src/shared/ByteBuffer.h#L138

    ByteBuffer& operator<<(uint8 value)
    {
        append<uint8>(value);
        return *this;
    }

so its not a shift by 0, but appending of value 0.

Upvotes: 11

edmz
edmz

Reputation: 8494

pkt is likely of a class-type which overloads operator<<; if it weren't so, all those statements would have no effect since it's result is not used. (pkt << 0 rather than pkt <<= 0).

Upvotes: 1

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