SafeInt Class

The latest version of this topic can be found at SafeInt Class.

Extends the integer primitives to help prevent integer overflow and lets you compare different types of integers.

Syntax

template<typename T, typename E = _SAFEINT_DEFAULT_ERROR_POLICY>  
class SafeInt;  

Parameters

Members

Public Constructors

Assignment Operators

Casting Operators

Comparison Operators

Arithmetic Operators

Logical Operators

Remarks

The SafeInt class protects against integer overflow in mathematical operations. For example, consider adding two 8-bit integers: one has a value of 200 and the second has a value of 100. The correct mathematical operation would be 200 + 100 = 300. However, because of the 8-bit integer limit, the upper bit will be lost and the compiler will return 44 (300 - 2⁸) as the result. Any operation that depends on this mathematical equation will generate unexpected behavior.

The SafeInt class checks whether an arithmetic overflow occurs or whether the code tries to divide by zero. In both cases, the class calls the error handler to warn the program of the potential problem.

This class also lets you compare two different types of integers as long as they are SafeInt objects. Typically, when you perform a comparison, you must first convert the numbers to be the same type. Casting one number to another type often requires checks to make sure that there is no loss of data.

The Operators table in this topic lists the mathematical and comparison operators supported by the SafeInt class. Most mathematical operators return a SafeInt object of type T.

Comparison operations between a SafeInt and an integral type can be performed in either direction. For example, both SafeInt<int>(x) < y and y > SafeInt<int>(x) are valid and will return the same result.

Many binary operators do not support using two different SafeInt types. One example of this is the & operator. SafeInt<T, E> & int is supported, but SafeInt<T, E> & SafeInt<U, E> is not. In the latter example, the compiler does not know what type of parameter to return. One solution to this problem is to cast the second parameter back to the base type. By using the same parameters, this can be done with SafeInt<T, E> & (U)SafeInt<U, E>.

For the shift operators, shifting more bits than exist for the template type will throw an ASSERT exception. This will have no effect in release mode. Mixing two types of SafeInt parameters is possible for the shift operators because the return type is the same as the original type. The number on the right side of the operator only indicates the number of bits to shift.

When you perform a logical comparison with a SafeInt object, the comparison is strictly arithmetic. For example, consider these expressions:

• SafeInt<uint>((uint)~0) > -1

• ((uint)~0) > -1

The first statement resolves to true, but the second statement resolves to false. The bitwise negation of 0 is 0xFFFFFFFF. In the second statement, the default comparison operator compares 0xFFFFFFFF to 0xFFFFFFFF and considers them to be equal. The comparison operator for the SafeInt class realizes that the second parameter is negative whereas the first parameter is unsigned. Therefore, although the bit representation is identical, the SafeInt logical operator realizes that the unsigned integer is larger than -1.

Be careful when you use the SafeInt class together with the ?: ternary operator. Consider the following line of code.

Int x = flag ? SafeInt<unsigned int>(y) : -1;  

The compiler converts it to this:

Int x = flag ? SafeInt<unsigned int>(y) : SafeInt<unsigned int>(-1);  

If flag is false, the compiler throws an exception instead of assigning the value of -1 to x. Therefore, to avoid this behavior, the correct code to use is the following line.

Int x = flag ? (int) SafeInt<unsigned int>(y) : -1;  

T and U can be assigned a Boolean type, character type, or integer type. The integer types can be signed or unsigned and any size from 8 bits to 64 bits.

E is the error handling mechanism that SafeInt uses. Two error handling mechanisms are provided with the SafeInt library. The default policy is SafeIntErrorPolicy_SafeIntException, which throws a SafeIntException Class exception when an error occurs. The other policy is SafeIntErrorPolicy_InvalidParameter, which stops the program if an error occurs.

There are two options to customize the error policy. The first option is to set the parameter E when you create a SafeInt. Use this option when you want to change the error handling policy for just one SafeInt. The other option is to define _SAFEINT_DEFAULT_ERROR_POLICY to be your customized error-handling class before you include the SafeInt library. Use this option when you want to change the default error handling policy for all instances of the SafeInt class in your code.

Requirements

Header: safeint.h

Namespace: msl::utilities

See Also

Miscellaneous Support Libraries Classes
SafeInt Library
SafeIntException Class