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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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b0rk (Julia Evans) on Twitter: “integer overflow”

Posted by jpluimers on 2025/10/16

Even seemingly simple data structures are worth explaining, especially when debugging. So I was glad with the explanation of [Wayback/Archive] Julia Evans on Twitter: “integer overflow”:

# integer overflow ## integers have a limited amount of space The 4 usual sizes for integers are 8 bits, 16 bits, 32 bits, and 64 bits ## the biggest 8-bit unsigned integer is 255 ... so what happens if you do 255 + 1? ## going above/below the limits is called overflow the result wraps around to the other side * 255 + 1 = 0 * 255 + 3 = 2 * 200 * 2 = 144 * 0 - 2 = 254 ## maximum numbers for different sizes bits: unsigned signed 8: 127 255 16: 32767 65535 32: 2 billion ~4 billion 64: ~9 quintillion ~18 quintillion ## overflows often don't throw errors computer (thinking): "255 + 1? that number is 8 bits, so the answer is 0! that's what you wanted right?" This can cause VERY tricky bugs ## some languages where integer overflow happens * Java/Kotlin * C/C++ * Rust * Swift * C# * SQL * R * Go * Dart * Lua * Python (only in numpy) Some throw errors on overflow, some don't, for some it depends on various factors. Look up how it works in your language!

–jeroen

This entry was posted on 2025/10/16 at 12:00 and is filed under Conference Topics, Conferences, Debugging, Development, Event, Software Development. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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