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MISRA C++:2008 Rule 5-0-6

An implicit integral or floating-point conversion shall not reduce the size of the underlying type

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Description

Rule Definition

An implicit integral or floating-point conversion shall not reduce the size of the underlying type.

Rationale

A conversion that reduces the size of the underlying type can result in loss of information. Unless you explicitly cast to the narrower type, it is not clear whether the loss of information is intended.

Polyspace Implementation

The checker flags implicit conversions that reduce the size of a type.

If the conversion is to a narrower integer with a different sign, then rule 5-0-4 takes precedence over rule 5-0-6. Only rule 5-0-4 is shown.

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

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typedef signed short int16_t;
typedef signed int int32_t;

void func ( )
  {
    int16_t   s16;;
    int32_t   s32;
    s16 = s32;   //Noncompliant
    s16 = static_cast< int16_t > ( s32 ); //Compliant
  }

In this example, the rule is violated when a type is implicitly converted to a narrower type. The violation does not occur if the conversion is explicit.

Check Information

Group: Expressions
Category: Required

Version History

Introduced in R2013b

See Also

Topics