QA·C Help - 2940

	2940	Constant: Result of implicit conversion is only representable in a two's complement implementation.

Conversion to signed

A negative value is being implicitly converted to a signed type and the value is such that it can only be represented in a signed type of this size in a two's-complement form. In practice, two's complement representation is almost universal in modern computers, but other binary representations do exist.

Message 2940 will be generated when:

the value -128 is assigned to an 8 bit signed type
the value -32768 is assigned to a 16 bit signed type
the value -2147483648 is assigned to a 32 bit signed type

Notice that on a 16 bit architecture:

32767 is a constant of type signed int
32768 is a constant of type signed long
-32768 is an expression of type signed long

The expression "-32767 - 1" is of type signed int - BUT its evaluation will result in overflow if the signed representation is not two's complement.

Example:


/*PRQA S 274,280,1278,2017,2982,2984,3120,3198,3210,3408,3447,3602,3606 ++*/
/***************************************************/
/* OPTIONS: -s int=16                              */
/***************************************************/

extern signed char  sca;
extern signed short ssa;
extern signed int   sia;

extern void foo(void)
{
    sca = -127;
    sca = -128;                         /* 2940 */
    sca = -129;                         /* 2850 */

    ssa = -32767;
    ssa = -32767 - 1;                   /* 2940 */
    ssa = -32769L;                      /* 2850 */

    sia = -32767;
    sia = -32767 - 1;                   /* 2940 */
}

See also:

2941 Definite: Result of implicit conversion is only representable in a two's complement implementation.
2942 Apparent: Result of implicit conversion is only representable in a two's complement implementation.
2943 Suspicious: Result of implicit conversion is only representable in a two's complement implementation.
2945 Constant: Result of cast is only representable in a two's complement implementation.
2946 Definite: Result of cast is only representable in a two's complement implementation.
2947 Apparent: Result of cast is only representable in a two's complement implementation.
2948 Suspicious: Result of cast is only representable in a two's complement implementation.

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