Re: read in movemail.c

[Jan D.]

Dan Nicolaescu wrote:

> CID: 29
> Checker: NEGATIVE_RETURNS (help)
> File: emacs/lib-src/movemail.c
> Function: main
> Description: Tracked variable "nread" was passed to a negative sink.
>
>
> 463           {
> 464             char buf[1024];
> 465     
> 466             while (1)
> 467               {
>
> Event negative_return_fn: Called negative-returning function "read"
> Event var_assign: NEGATIVE return value of "read" assigned to signed variable 
> "nread"
> Also see events: [var_assign][negative_returns]
>
> 468                 nread = read (indesc, buf, sizeof buf);
>
> Event negative_returns: Tracked variable "nread" was passed to a negative sink.
> Also see events: [negative_return_fn][var_assign]
>
> 469                 if (nread != write (outdesc, buf, nread))
> 470                   {
> 471                     int saved_errno = errno;
> 472                     unlink (outname);
> 473                     errno = saved_errno;
> 474                     pfatal_with_name (outname);
> 475                   }
> 476                 if (nread < sizeof buf)
> 477                   break;
>
>
>
> Is it portable to just pass "nread" to write and compare the return
> values? Maybe "nread" can be checked before?

nread might be -1 on error from read, so then the call to write would be 
bad, as the third argument is a size_t (unsigned) so -1 becomes a large 
value.  Better is to check for -1 and 0 (end of file) before doing the 
write.

   Jan D.