[previous] 4393 [next] A composite expression of 'essentially signed' type (%1s) is being cast to a different type category, '%2s'.
Arithmetic type - Composite expressions

This message is issued whenever a composite expression of essentially signed type has been cast to a different essential type category.

It is a common misconception among programmers that the type in which the arithmetic operation is evaluated is influenced by the cast-to type. Instead, the type of the expression is determined solely from the type of its operands after any integral promotion. Therefore, an overflow may occur, which could be avoided if operands were cast instead.

For example: 


/*PRQA S 1-9999 ++*/
/*PRQA S 4393 --*/

void foo (unsigned b);

unsigned f4393 (short a)
{
  foo ((unsigned) (a + 1));    /* 4393 */
  
  return ((unsigned) (a * 2)); /* 4393 */
}

For the purposes of QAC conversion messages, types are ordered according to the configured size (-s option), by default; hence for a typical 32 bit configuration, types int and long will be considered equivalent. However, when the -strictrank option is specified, types will be ordered according to their rank; consequently int will be considered narrower than long.

MISRA-C:2004 Rules applicable to message 4393:

Rule  10.3  (Required) The value of a complex expression of integer type shall only be cast to a type of the same signedness that is no wider than the underlying type of the expression.

QA·C Source Code Analyser 8.1
MISRA-C:2004 Compliance Module 3.2
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