# Conventions on struct copying? 4 messages from 2014-06-18 to 2014-06-20. Participants: brian m. carlson, Junio C Hamano, Jason Pyeron. Thread: https://gitlist.dev/t/36959 ## brian m. carlson, 2014-06-18 23:31 Subject: Conventions on struct copying? Message-ID: <20140618233129.GK368384@vauxhall.crustytoothpaste.net> URL: https://gitlist.dev/e/20140618233129.GK368384%40vauxhall.crustytoothpaste.net ``` 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 / brian with sandals: Houston, Texas, US +1 832 623 2791 | http://www.crustytoothpaste.net/~bmc | My opinion only OpenPGP: RSA v4 4096b: 88AC E9B2 9196 305B A994 7552 F1BA 225C 0223 B187 ``` ## Junio C Hamano, 2014-06-19 17:10 Subject: Re: Conventions on struct copying? Message-ID: URL: https://gitlist.dev/e/xmqqvbrwhlki.fsf%40gitster.dls.corp.google.com In-Reply-To: <20140618233129.GK368384@vauxhall.crustytoothpaste.net> ``` "brian m. carlson" writes: > I don't know of any place we explicitly copy structs like > this,... which should be a reason enough. The first concrete guideline is "just imitate the existing code". > but I don't know of any prohibition against it, either. So now you know ;-). ``` ## Jason Pyeron, 2014-06-19 17:22 Subject: RE: Conventions on struct copying? Message-ID: <5A7F0CEE2DEC4F1B825568DB8358D397@black> URL: https://gitlist.dev/e/5A7F0CEE2DEC4F1B825568DB8358D397%40black In-Reply-To: ``` > -----Original Message----- > From: Junio C Hamano > Sent: Thursday, June 19, 2014 13:11 > > "brian m. carlson" writes: > > > I don't know of any place we explicitly copy structs like > > this,... > > which should be a reason enough. The first concrete guideline is > "just imitate the existing code". > > > but I don't know of any prohibition against it, either. > > 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 -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- - - - Jason Pyeron PD Inc. http://www.pdinc.us - - Principal Consultant 10 West 24th Street #100 - - +1 (443) 269-1555 x333 Baltimore, Maryland 21218 - - - -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- This message is copyright PD Inc, subject to license 20080407P00. ``` ## brian m. carlson, 2014-06-20 01:26 Subject: Re: Conventions on struct copying? Message-ID: <20140620012608.GA856079@vauxhall.crustytoothpaste.net> URL: https://gitlist.dev/e/20140620012608.GA856079%40vauxhall.crustytoothpaste.net In-Reply-To: <5A7F0CEE2DEC4F1B825568DB8358D397@black> ``` On Thu, Jun 19, 2014 at 01:22:44PM -0400, Jason Pyeron wrote: > > -----Original Message----- > > From: Junio C Hamano > > Sent: Thursday, June 19, 2014 13:11 > > > > "brian m. carlson" writes: > > > > > I don't know of any place we explicitly copy structs like > > > this,... > > > > which should be a reason enough. The first concrete guideline is > > "just imitate the existing code". 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. > > > but I don't know of any prohibition against it, either. > > > > So now you know ;-). > > To expand, on that do not trust the compiler to do deep copies. 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. -- brian m. carlson / brian with sandals: Houston, Texas, US +1 832 623 2791 | http://www.crustytoothpaste.net/~bmc | My opinion only OpenPGP: RSA v4 4096b: 88AC E9B2 9196 305B A994 7552 F1BA 225C 0223 B187 ```