RFR-8008118 (original) (raw)

Martin Buchholz martinrb at google.com
Wed Apr 10 20:44:18 UTC 2013

Christos, I think you may have overlooked the subtlety that pathv is not a const pointer - it just looks like one.

cat cast.c && echo --- && gcc -Wall -Wcast-qual cast.c #include <stdio.h> #include <stdlib.h>

int main(int argc, char *argv[]) { const char **p = (const char **) malloc(5); char *q = (char *)p + 3; printf("%p %p\n", p, q); return 0; }

On Wed, Apr 10, 2013 at 1:30 PM, Christos Zoulas <christos at zoulas.com>wrote:

On Apr 10, 11:54am, martinrb at google.com (Martin Buchholz) wrote: -- Subject: Re: RFR-8008118

| > 1. We did we switch from NEW() to xmalloc()? Why is the xmalloc cast | > needed? | | NEW is for allocating homogeneous arrays, but here the memory block is | being used for both chars and pointers. I did not know that. Why the cast though? xmalloc() returns void *, no? Extraneous casts are bad because they hide conversion errors. For example, if you don't have the xmalloc prototype in scope, without the cast you get a warning of casting integer to pointer of different size. With the cast you get the wrong data assigned to the pointer. | > 2. I would not declare pathv "const char **", but "char **", and then | > cast the return if needed. This will make life easier in the future | > if we decide to turn on warnings about const-castaways. | > | > | I believe the current code doesn't cast away const and doesn't write to | const. The only cast is to the return from xmalloc, which is expected. | What might a compiler warn about? It is casting away const before the memcpy: + p = (char *) pathv + pathvsize; Try to compile with -Wcast-qual. christos

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