MISRA Discussion Forums

Hi

Question about Rule 12.9: The unary minus operator shall not be applied to an expression whose underlying type is unsigned.

Code:
uint32_t u_int_a;

uint32_t u_int_b;

u_int_a = -u_int_b;

1. Is this incorrect?
2. Shows this example, what the rule 12.9 mean?

4. Is this correct? (a = int)

Code:
uint32_t int_a;

uint32_t u_int_b;

u_int_a = -(int32_t)u_int_b;

5. Is this correct, too? (a = uint)

Code:
uint32_t u_int_a;

uint32_t u_int_b;

u_int_a = -(int32_t)u_int_b;

6. I think it it is correct to rule 12.9, but breach 10.1. Right?

7. Have somebody good examples for rule breaks? And how to solve it?

best regards,
Manni

Code:
uint32_t u_int_a; 

uint32_t u_int_b; 

u_int_a = -u_int_b;

This is a violation of rule 12.9 since the underlying type of u_int_b is unsigned.

----

Code:
int32_t int_a;    /* changed from uint32_t */

uint32_t u_int_b; 

int_a = -(int32_t)u_int_b; /* changed u_int_a to int_a */

This is allowed.

----

Code:
uint32_t u_int_a; 

uint32_t u_int_b; 

u_int_a = -(int32_t)u_int_b;

This is compliant with rule 12.9, but violates 10.1. because of the change of signedness on assignment.

Manni

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