Re: [PATCH] Drivemap module

[Colin D Bennett]

On Tue, 05 Aug 2008 01:10:25 +0200
Javier Martín <address@hidden> wrote:

> Besides, sometimes checks like "if (a=b)", or more
> frequently "if (a=f())" are intentionally used in C, so the error
> might become even more difficult to spot and correct.

Respect and heed the gcc warnings!!

Note that gcc will warn you (you *are* using -Wall, at least, right?)
if you try to do

  if (a = b)

but if you really mean it, you should surround the expression with an
extra pair of parentheses:

  if ((a = b))

Use of the value of an assignment in an expression is common in code
like

  if ((n = read (fd, buf, sz)) > 0)
    /* ... use the data in buf ... */

Here's an example showing gcc being helpful:

  $ cat a.c
  int f()
  {
      int a = 1;
      int b;
      if ((b = a))
        return 1;
      return 0;
  }
  $ cat b.c
  int f()
  {
      int a = 1;
      int b;
      if (b = a)
        return 1;
      return 0;
  }
  $ gcc -Wall -c a.c
  $ gcc -Wall -c b.c
  b.c: In function ‘f’:
  b.c:5: warning: suggest parentheses around assignment used as truth
  $ 

> New version of the patch follows. I must say that the discussion here
> has become pretty interesting without degrading into flamewarring -
> who whats to call Mr. Torvalds and Prof. Tanembaum? ^^

Well, it sounds to me like you are trying your best to set Marco ablaze,
but he is delightfully fire-retardant.

Regards,
Colin