Conventions on struct copying?

I'm still working on the struct object_id patches, and I had a style question. In several places throughout the code, we do something like this:

  unsigned char a[20], b[20];

  /* do some stuff with b */
  hashcpy(a, b);

I could implement an oidcpy that does the same thing.

  struct object_id a, b;

  /* do some stuff with b */
  oidcpy(&a, &b);

Or I could just write that as:

  a = b;

and let the compiler do the heavy lifting. Is there any reason that we'd want the function for that purpose, or is it okay to just use the assignment? I don't know of any place we explicitly copy structs like this, but I don't know of any prohibition against it, either.

"brian m. carlson" <sandals@crustytoothpaste.net> writes:

which should be a reason enough. The first concrete guideline is "just imitate the existing code".

So now you know ;-).

To expand, on that do not trust the compiler to do deep copies.

http://stackoverflow.com/questions/2302351/assign-one-struct-to-another-in-c

Hit #1 on https://www.google.com/search?q=c+assignment+of+struct

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On Thu, Jun 19, 2014 at 01:22:44PM -0400, Jason Pyeron wrote:

Right. The reason I asked is that most of our structures end up containing pointers, so it wouldn't make sense to do the equivalent of a memcpy on them anyways. This is just data, so I thought it might be different. I'll implement an oidcpy function to do the work.

I'm not.  The definition looks like;

  struct object_id {
    unsigned char sha1[20];
  };

I only want it to memcpy those 20 bytes; there's no pointers or anything to complicate it.