What is the benefit of terminating if … else if constructs with an else clause?

Question

Our organization has a required coding rule (without any explanation) that:

if … else if constructs should be terminated with an el

Answer 1

Your company followed MISRA coding guidance. There are a few versions of these guidelines that contain this rule, but from MISRA-C:2004^†:

Rule 14.10 (required): All if … else if constructs shall be terminated with an else clause.

This rule applies whenever an if statement is followed by one or more else if statements; the final else if shall be followed by an else statement. In the case of a simple if statement then the else statement need not be included. The requirement for a final else statement is defensive programming. The else statement shall either take appropriate action or contain a suitable comment as to why no action is taken. This is consistent with the requirement to have a final default clause in a switch statement. For example this code is a simple if statement:

if ( x < 0 )
{
 log_error(3);
 x = 0;
} /* else not needed */

whereas the following code demonstrates an if, else if construct

if ( x < 0 )
{
 log_error(3);
 x = 0;
}
else if ( y < 0 )
{
 x = 3;
}
else /* this else clause is required, even if the */
{ /* programmer expects this will never be reached */
 /* no change in value of x */
}

In MISRA-C:2012, which supersedes the 2004 version and is the current recommendation for new projects, the same rule exists but is numbered 15.7.

Example 1: in a single if statement programmer may need to check n number of conditions and performs single operation.

if(condition_1 || condition_2 || ... condition_n)
{
   //operation_1
}

In a regular usage performing a operation is not needed all the time when if is used.

Example 2: Here programmer checks n number of conditions and performing multiple operations. In regular usage if..else if is like switch you may need to perform a operation like default. So usage else is needed as per misra standard

if(condition_1 || condition_2 || ... condition_n)
{
   //operation_1
}
else if(condition_1 || condition_2 || ... condition_n)
{
  //operation_2
}
....
else
{
   //default cause
}

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^† Current and past versions of these publications are available for purchase via the MISRA webstore (via).