Integer overflow: Difference between revisions

Revision as of 10:10, 5 May 2015

Revision as of 11:21, 5 May 2015

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In some situations, a program may make the assumption that a variable always contains a positive value. If the variable has a signed integer type, an overflow can cause its value to wrap and become negative. This overflow violates the program's assumption and may lead to unintended behavior. Similarly, subtracting from a small unsigned value may cause it to wrap to a large positive value which may also be an unexpected behavior. Multiplying or adding two integers may result in a value that is non-negative, but unexpectedly small. If this number is used as the number of bytes to allocate for a buffer, the buffer will be allocated unexpectedly small, leading to a potential buffer overflow.

SomeProgramming languages, suchimplement asvarious mitigation techniques against an accidental overflow: [[Ada (programming language)|Ada]], [[Seed7]] (and certain variants of functional languages), provide mechanisms to make accidental overflows trigger an exception condition. Inon contrastoverflow, while [[Python (programming language)|Python]] seamlessly converts ainternal numberrepresentation thatof becomesthe toonumber largeto formatch anits integergrowth, toeventually arepresenting it as <code>long</code> whose capability is only limited by the available memory.<ref>[https://www.python.org/doc/1.4/ref/ref5.html Python documentation], section 5.1 Arithmetic conversions.</ref> (This occurred in Python 2.4.)<ref>[https://www.python.org/dev/peps/pep-0237/ Python Enhancement Proposal 237]</ref>

==Techniques for mitigating integer overflow problems==