MISRA C:2012 Rule 10.6

The value of a composite expression shall not be assigned to an object with wider essential type

Description

Rule Definition

The value of a composite expression shall not be assigned to an object with wider essential type¹ .

Rationale

A composite expression is a nonconstant expression using a composite operator. In the Essential Type Model, composite operators are:

• Multiplicative (*, /, %)

• Additive (binary +, binary -)

• Bitwise (&, |, ^)

• Shift (<<, >>)

• Conditional (?, :)

Unary operators such as ~ and unary + or - are also considered composite operators.

If you assign the result of a composite expression to a larger type, the implicit conversion can result in loss of value, sign, precision, or layout.

For more information on essential types, see Essential Types in MISRA C Rules 10.x.

Troubleshooting

If you expect a rule violation but do not see it, refer to Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Check Information

Group: The Essential Type Model

Category: Required

AGC Category: Advisory

Version History

R2021b: Checker flags unary operations whose output is assigned to wider essential types

The checker now flags unary composite operators when their output is assigned to an object with a wider essential type. For instance:

#include<stdint.h>
void foo(uint8_t u8a, uint16_t u16a){
   u8a = ~u8a;                       /* Compliant*/
   u16a = ~u8a;                      /* Noncompliant */
  
}