MISRA C++:2023 Rule 7.0.5

Integral promotion and the usual arithmetic conversions shall not change the signedness or the type category of an operand

Since R2024b

Description

Rule Definition

Integral promotion and the usual arithmetic conversions shall not change the signedness or the type category of an operand.

Rationale

Some conversions from signed to unsigned data types can lead to implementation-defined behavior. You can see unexpected results from the conversion.

Polyspace Implementation

The checker flags implicit conversions from a signed to an unsigned integer data type or vice versa.

The checker assumes that ptrdiff_t is a signed integer.

Troubleshooting

If you expect a rule violation but Polyspace^® does not report it, see Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

Implicit Conversions that Change Signedness

typedef char int8_t;
typedef unsigned char uint8_t;

void func()
  {
    int8_t s8;
    uint8_t u8;

    s8 = u8; //Noncompliant
    u8 = s8 + u8; //Noncompliant
    u8 = static_cast< uint8_t > ( s8 ) + u8; //Compliant
}

In this example, the rule is violated when a variable with a variable with signed data type is implicitly converted to a variable with unsigned data type or vice versa. If the conversion is explicit, as in the preceding example, the rule violation does not occur.

Check Information

Group: Standard Conversions

Category: Required

Version History

Introduced in R2024b