What is an integer overflow error?

language-agnostic integer-overflow
David picture David · Apr 14, 2010 · Viewed 21.3k times · Source

What is an integer overflow error? Why do i care about such an error? What are some methods of avoiding or preventing it?

Answer

John picture John · Apr 14, 2010

Integer overflow occurs when you try to express a number that is larger than the largest number the integer type can handle.

If you try to express the number 300 in one byte, you have an integer overflow (maximum is 255). 100,000 in two bytes is also an integer overflow (65,535 is the maximum).

You need to care about it because mathematical operations won't behave as you expect. A + B doesn't actually equal the sum of A and B if you have an integer overflow.

You avoid it by not creating the condition in the first place (usually either by choosing your integer type to be large enough that you won't overflow, or by limiting user input so that an overflow doesn't occur).

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