Hello Alex, On Sat, 5 Sep 2020 at 11:37, Alejandro Colomar <colomar.6.4.3@xxxxxxxxx> wrote: > > Hi Michael, > > On 9/5/20 10:27 AM, Michael Kerrisk (man-pages) wrote: [...] > So, I've still not processed patches 21, 22, and 29. And in review, > > I see that I am wondering about whether I should maintain 1, 5, 17, > > 18, and 19. These all involve the use of malloc() or similar. > > > > The existing pattern was something like: > > > > struct mytype *x; // Or some simple type such as 'int' > > ... > > x = malloc(n * sizeof(struct mytpe)); > > Not to forget `malloc(sizeof(struct mytpe) * n);` <Cough> yes <cough>... > > and your patches change it to: > > > > struct mytype *x; > > ... > > x = malloc(n * sizeof(*x));> > > I'm not sure that always helps readability. > > > > Part of the problem is the use of C90 in the code. > > > > Do you both agree with me that both of the following c99 > > forms are better than the original: > > > > struct mytype *x = malloc(n * sizeof(struct mytpe)); > > struct mytype *x = malloc(n * sizeof(*x)); > > > > ? > > Yes, I would say both of these are an improvement. > > > > I *think* I mildly prefer the first form, but I'm open to > > arguments that the latter form is preferable. Of course, the > > fact that there might be more than one point where an 'alloc' > > is done and assigned to 'x' may influence the argument. Thus > > > > > > struct mytype *x = malloc(n * sizeof(struct mytpe)); > > ... > > x = malloc(p * sizeof(struct mytype)); > > > > vs > > > > struct mytype *x = malloc(n * sizeof(*x)); > > ... > > x = malloc(p * sizeof(*x)); > > In case there are 2 or more allocs, in general, I prefer the name of the > variable. Yes, by the time I'd written the two allocs examples, I'd started to lean that way too, but didn't say so because I wanted to hear your independent perspective . > In case there is only 1 alloc in the same line as the declaration, I > still prefer the name of the variable: for consistency, and because some > day you may add another alloc, and then separate the original > declaration+alloc in two lines, and forget to fix sizeof to use the name > of the variable. Yes. > The cases where I see the type much better are cases where it is > impossible for the type to change (and if it ever changed it would be an > accident and cause a deserved bug) such as in those cases where you > really need an (u)int64_t because of the API. Yes. > There's also cases where in real code I would prefer the name of the > variable (to avoid future bugs because of type change), but in the man > pages it is clearer if you write the type to be more explicit and > consistent. Example: queue.3 (PATCH 24/34): It's clearer if you > consistently use the type across all the code (and it may be therefore > better to use it in the man-pages), because the name of the variable > looks like it's different from one alloc to the next, but I can imagine > some real code implementing a TAILQ and later deciding to use a CIRCLEQ, > and if any of the types in the allocation are not updated accordingly, > there will appear bugs, while if the name of the node is used for > allocating the memory, the transition will be really simple. Agreed. I've applied patches 21, 22, and 29. And then in line with our discussion above, I moved some pages to the style discussed above: struct mytype *x = malloc(sizeof(*x)); See commit 48d05103071830b6708a3ecabeddcdef5f3daa44. Thanks for your input Alex, it's been really helpful! Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
