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Rule 15.7, 16.4, side-effects and statements. - Printable Version

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+---- Thread: Rule 15.7, 16.4, side-effects and statements. (/showthread.php?tid=1330)

Rule 15.7, 16.4, side-effects and statements. - RichardC - 04-04-2017

Rule 15.7 "if...else if terminated by else" refers to "Rule 16.5". However, there appears to be a stronger relationship with 16.4: "Every switch shall have a default label". Should 16.4 be linked to 15.7?

In my opinion, there is a slight inconsistency between the rule rationale for 15.7 and 16.4 and what might be read as being covered.

Starting with Rule 15.7, the amplification requires a side-effect or a comment. Would you agree that this interpretation results in the following examples being 'non-compliant'?

Code:
void f1 (int x, int y)
  {
    for (int i = 0; i < 10; ++i)
    {
      if (i % x )
      {
      }
      else if (i % y)
      {
      }
      else
      {
        break;
      }
      /* Non-Compliant? Not a side-effect and not a comment */
    }
  }

  void f2 (int x, int y)
  {
    if (x != 0)
    {
    }
    else if (y != 0)
    {
    }
    else
    {
      return;
    }
    /* Non-Compliant? Not a side-effect and not a comment.
     * Non-compliant to advisory 15.5 */
  }

  void f3 (int x, int y)
  {
    if (x != 0)
    {
    }
    else if (y != 0)
    {
    }
    else
    {
      ;
    }
    /* Non-Compliant? Not a side-effect and not a comment. */
  }

  void f4 (int x, int y)
  {
    if (x != 0)
    {
    }
    else if (y != 0)
    {
    }
    else
    {
      goto END;
    }
    /* Non-Compliant? Not a side-effect and not a comment. */

  END:
    ;
  }

  void f5 (int x, int y)
  {
    for (int i = 0; i < 10; ++i)
    {
      if (i % x)
      {
      }
      else if (i % y)
      {
      }
      else
      {
        if (i != x)
        {
          if (i != y)
          {
            if ((i*i) > (x*y))
            {
            }
          }
        }
      }
      /* Non-Compliant? No comment or side-effect */
    }
  }

And the following examples would be compliant:

Code:
void f6 (int x, int y)
  {
    if (x != 0)
    {
    }
    else if (y != 0)
    {
    }
    else
    {
      /* Compliant */
    }
  }

  void f7 (int x, int y)
  {
    if (x != 0)
    {
    }
    else if (y != 0)
    {
    }
    else
      /* Compliant, but Non-Compliant with 15.6 */ ;
  }

  void f8 (int x, int y)
  {
    for (int i = 0; i < 10; ++i)
    {
      if (i % x)
      {
      }
      else if (i % y)
      {
      }
      else
      {
        if (i != x)
        {
          if (i != y)
          {
            if ((i*i) > (x*y))
            {
              /* Compliant? Comment "appears" in else. */
            }
          }
        }
      }
    }
  }

For Rule 16.4, the amplification requires a 'statement'. What do you feel is that status of the following examples?

Code:
void f9 (int x)
  {
    switch (x)
    {
    case 0:
      x+=1;
      break;
    case 1:
      x+=2;
      break;
    case 3:
      x+=3;
      break;
    default:
      ;
      break;
    }
    /* Compliant? Is ';' a statement? */

  }

  void fA (int x)
  {
    switch (x)
    {
    case 0:
      x+=1;
      break;
    case 1:
      x+=2;
      break;
    case 3:
      x+=3;
      break;
    default:
      { }
      break;
    }
    /* Compliant? Depends on interpretation of 16.1 regarding { } is a compound statement */
  }

  void fB (int x)
  {
    switch (x)
    {
    case 0:
      x+=1;
      break;
    case 1:
      x+=2;
      break;
    case 3:
      x+=3;
      break;
    default:
      { { } }
      break;
    }
    /* Compliant? Similar to fA */
  }

  void fC (int x)
  {
    switch (x)
    {
    case 0:
      x+=1;
      break;
    case 1:
      x+=2;
      break;
    case 3:
      x+=3;
      break;
    default:
      /* Compliant */
      break;
    }
  }

My reading of the Rationale is that the goal is have a 'defensive' comment unless the else does something, ie. the comment acts as a form of "Annotation".


Alternatively, going just from the rationale, I would mark the above functions as Compliant/Non-Compliant as follows:
  • f1: Compliant
  • f2: Compliant, Non-Compliant with rule 15.5.
  • f3: Non-Compliant
  • f4: Compliant
  • f5: Compliant
  • f6: Compliant
  • f7: Compliant, Non-Compliant with Rule 15.6
  • f8: Compliant (not because of nested comment)
  • f9: Non-Compliant
  • fA: Non-Compliant
  • fB: Compliant

What is the view of the MISRA C group on this?