what means about "Before preprocessing" in Rule[14.3]

[linglingma]

"Before preprocessing, a null statement shall only occur on a
line by itself; it may be followed by a comment provided that
the first character following the null statement is a white-space
character." in this rule,why "Before preprocessing"is used as a condition?
Thanks!

[misra-c]

Consider the following code fragment:

Code:

void fn ( bool_t b )
{
   if ( b );   /* Non-compliant */
   {
      DO_SOMETHING;
   }
}

In the above DO_SOMETHING appears to be a (non-null) statement. However this depends on the value of the macro after pre-processing.

If the macro is defined as

Code:

#define DO_SOMETHING

then the DO_SOMETHING line is actually a null statement which appears on a line by itself. In order to catch this, the source code before pre-processing must be considered. Pre-processing will simply remove the DO_SOMETHING token sequence.

Rule 14.3 is also designed to catch the accidental use of null statements by the unintentional insertion of a ';'. The non-compliant line is the example above shows how they can lead to unexpected results, as what appears to be the body of the if statement will always be executed.

[gs]

However, according to http://www.misra-c2.com/forum/viewtopic.php?t=264, the line with the DO_SOMETHING macro usage is still non-compliant if the macro has the given definition, yes?

[misra-c]

Yes, it is non-compliant.