What Happens When Unsigned Integers Overflow in C/C ?

C/C Unsigned Integer Overflow: Understanding "Wrapping Around"

In integer security, one aspect to consider is the behavior of unsigned integer overflow. As mentioned in an article, "a computation involving unsigned operands can never overflow." This concept may be unfamiliar to some developers. Let's explore what this means.

What is Unsigned Integer Overflow?

Unsigned integers are non-negative whole numbers, and their range is limited by the size of their storage type. For example, a 32-bit unsigned integer has a range from 0 to 4,294,967,295.

When performing arithmetic operations with unsigned integers, the result can exceed the maximum value representable by the type. Instead of overflowing, however, the result "wraps around" to the smallest possible value for that type.

Example: Wrapping Around

Consider the addition of UINT_MAX (the maximum 32-bit unsigned integer) and 1:

UINT_MAX + 1 == 0

Instead of overflowing to a negative value, the result wraps around to 0. This is analogous to the modulo operation, where the result is "wrapped around" within a specified range.

Consequences of Unsigned Integer Overflow

Unsigned integer overflow can lead to unexpected results and security vulnerabilities if not properly anticipated. For instance, if a program expects a counter to start at a high value and increment continuously, an overflow could reset the counter to 0 prematurely.

Conclusion

While unsigned integer overflow may seem counterintuitive, it is an important aspect to be aware of in C/C . Understanding the concept of "wrapping around" is crucial for writing secure and reliable code that accounts for the potential pitfalls associated with unsigned integer arithmetic.

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