CODEWITHSUNDEEP
c++protocolsmultibyte
Tony the Pony
Tony the Pony

Reputation: 41397

C++: How to read and write multi-byte integer values in a platform-independent way?

I'm developing a simple protocol that is used to read/write integer values from/to a buffer. The vast majority of integers are below 128, but much larger values are possible, so I'm looking at some form of multi-byte encoding to store the values in a concise way.

What is the simplest and fastest way to read/write multi-byte values in a platform-independent (i.e. byte order agnostic) way?

Upvotes: 1

Views: 1501

Answers (5)

DevSolar
DevSolar

Reputation: 70293

XDR format might help you there. If I had to summarize it in one sentence, it's a kind of binary UTF-8 for integers.

Edit: As mentioned in my comment below, I "know" XDR because I use several XDR-related functions in my office job. Only after your comment I realized that the "packed XDR" format I use every day isn't even part of the official XDR docs, so I'll describe it seperately.

The idea is thus:

  • inspect most-significant bit of byte.
    • If it is 0, that byte is the value.
    • if it is 1, the next three bits give "byte count", i.e. number of bytes in value.
      • mask out top nibble (flag bit plus byte count), concatenate the appropriate number of bytes and you've got the value.

I have no idea if this is a "real" format or my (former) coworker created this one himself (which is why I don't post code).

Upvotes: 3

Nemo
Nemo

Reputation: 71535

Google's protocol buffers provide a pre-made implementation that uses variable-width encodings.

Upvotes: 1

AProgrammer
AProgrammer

Reputation: 52294

Text would be my first choice. If you want a varying length binary encoding you have two basic choices:

  • a length indication
  • an end marker

You obviously make merge those with some value bits.

  • For a length indication that would give you something where the length and some bits are given together (see for instance UTF-8),

  • For an end marker, you can for instance state that MSB set indicates the last byte and thus have 7 data bits per byte.

Other variants are obviously possible.

Upvotes: 2

KitsuneYMG
KitsuneYMG

Reputation: 12901

You could try Network Byte Order

Upvotes: 1

Victor Zamanian
Victor Zamanian

Reputation: 3180

You might be interested in the following functions:

htonl, htons, ntohl, ntohs - convert values between host and network byte order

   uint32_t htonl(uint32_t hostlong);
   uint16_t htons(uint16_t hostshort);
   uint32_t ntohl(uint32_t netlong);
   uint16_t ntohs(uint16_t netshort);

man byteorder

Upvotes: 2

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