[previous] 1891 [next] A composite expression of 'essentially unsigned' type (%1s) is being implicitly converted to a wider unsigned type, '%2s'.
Arithmetic type - Composite expressions

This message is issued whenever a composite expression of essentially unsigned type undergoes a usual arithmetic conversion to a wider unsigned integer type.

It is a common misconception among programmers that the type in which the composite expression is evaluated is influenced by the wider type. Instead, the type of the expression is determined solely from the type of its operands after any integral promotion. Therefore, wraparound may occur, which could be avoided if the operands were cast to the wider type, or rearranged so that wider operands appear first.

For example: 


/*PRQA S 1-9999 ++*/
/*PRQA S 1891 --*/

unsigned f1891 (unsigned short a, unsigned b)
{
  b = (a + 1) + b;          /* 1891 */

  return ((a * 2) - b);     /* 1891 */
}

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 1891:

Rule  10.1  (Required) The value of an expression of integer type shall not be implicitly converted to a different underlying type if: a) it is not a conversion to a wider integer type of the same signedness, or b) the expression is complex, or c) the expression is not constant and is a function argument, or d) the expression is not constant and is a return expression

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