Re: [PATCH 4 of 9] Fix comparison signedness warnings

["Matthias Andree" <matthias.andree@xxxxxx>]

Am 07.08.2010, 07:46 Uhr, schrieb Michael Elkins:

> Alternate version with addition check to make sure cast is safe.
>
> # HG changeset patch
> # User Matthias Andree <matthias.andree@xxxxxx>
> # Date 1281124373 -7200
> # Branch HEAD
> # Node ID f6590ddfaf4f1317b85345156a62397f1b530213
> # Parent  12ffab6683cd85ed8407683ef377f20798d126b4
> Fix comparison signedness warnings.
>
> diff -r 12ffab6683cd -r f6590ddfaf4f buffy.c
> --- a/buffy.c   Fri Aug 06 21:52:36 2010 +0200
> +++ b/buffy.c   Fri Aug 06 21:52:53 2010 +0200
> @@ -456,13 +456,11 @@
>     BUFFY *tmp;
>     char path[_POSIX_PATH_MAX];
>     char buffylist[2*STRING];
> -  int pos;
> -  int first;
> +  size_t pos = 0;
> +  int first = 1;
>    int have_unnotified = BuffyNotify;
> -  pos = 0;
> -  first = 1;
>     buffylist[0] = 0;
>     pos += strlen (strncat (buffylist, _("New mail in "), sizeof  
> (buffylist) - 1 - pos)); /* __STRNCAT_CHECKED__ */
>     for (tmp = Incoming; tmp; tmp = tmp->next)
> @@ -474,7 +472,7 @@
>       strfcpy (path, tmp->path, sizeof (path));
>       mutt_pretty_mailbox (path, sizeof (path));
> -    if (!first && pos + strlen (path) >= COLS - 7)
> +    if (!first && (COLS - 7 >= 0) && (pos + strlen (path) >=  
> (size_t)COLS - 7))

Good catch. I was assuming that. Depending on compiler, it will be more  
efficient to write COLS >= 7 :)

Would something like

/* compare the first size_t argument a to the signed-typed argument b */
#define SIZET_GE(a, b)  ((b) >= 0 && (a) >= (size_t)(b))
#define SIZET_GT(a, b)  ((b) >= 0 && (a) > (size_t)(b))

be useful? That would allow writing:

        if (!first && SIZET_GE(pos + strlen(path), COLS - 7))

(C sometimes sucks because it's too close to the bits, meaning it's  
sometimes painfully low-level to get every corner case safe. I say that as  
someone who's been using C for two decades now.)

--
Matthias Andree