CERT C++: INT50-CPP

The issue Casting to out-of-range enumeration value occurs when you cast an arithmetic value to an enumeration but the arithmetic value is too big for the enumeration.

Whether an arithmetic value is too big for an enumeration depends on the underlying type of the enumeration:

The signedness of the assumed underlying type follows the signedness of the enumerators.

The result of casting to an out-of-range enumeration value is unspecified for C++ version older than C++17. For C++17 and later, this operation results in undefined behavior. Such casts might compile correctly but result in unexpected or incorrect behavior.

To fix this issue, use any of these fixes:

In this example, the int variable value is cast to an the enum type myEnum. The unscoped enumeration myEnum does not have a fixed underlying type. Polyspace assumes that the range of myEnum is [0.. 3]. Because value is an integer, its range is wider than [0.. 3]. Because value can be out of range for myEnum, the static_cast operation can result in an unspecified value. Polyspace reports a violation on the operation.

The bound checking cannot prevent the out-of-range cast because the bound is checked after the cast operation.

enum myEnum {
  One,
  Two,
  Three
};
 
void foo(int value) {
  myEnum enum_val = static_cast<myEnum>(value); //Noncompliant
 
  if (enum_val < One || enum_val > Three) {
    // Handle error
  }
}

To fix this violation, perform the bound check before the cast.

enum myEnum {
  One,
  Two,
  Three
};
 
void foo(int value) {
  if (value < One || value > Three) {
    // Handle error
	return;
  }
  myEnum enum_val = static_cast<myEnum>(value); //Compliant
 
  
}

Fix this violation by using scoped enumerations. In this case, the range of myEnum is same as that of int and the cast is in range.

enum class myEnum {
  One,
  Two,
  Three
};
 
void foo(int value) {
  //..
  myEnum enum_val = static_cast<myEnum>(value); //Compliant
 
  
}

Fix this violation by using enum with fixed underlying type. In this case, the range of myEnum is the same as that of int and the cast is in range.

enum myEnum:int {
  One,
  Two,
  Three
};
 
void foo(int value) {
  //..
  myEnum enum_val = static_cast<myEnum>(value); //Compliant
 
  
}