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Asked: 2026-05-16T16:53:21+00:00

Edited to include proper standard reference thanks to Carl Norum. The C standard states

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Edited to include proper standard reference thanks to Carl Norum.

The C standard states

If an exceptional condition occurs during the evaluation of an expression (that is, if the result is not mathematically defined or not in the range of representable values for its type), the behavior is undefined.

Are there compiler switches that guarantee certain behaviors on integer overflow? I’d like to avoid nasal demons. In particular, I’d like to force the compiler to wrap on overflow.

For the sake of uniqueness, let’s take the standard to be C99 and the compiler to be gcc. But I would be interested in answers for other compilers (icc, cl) and other standards (C1x, C89). In fact, just to annoy the C/C++ crowd, I’d even appreciate answers for C++0x, C++03, and C++98.

Note: International standard ISO/IEC 10967-1 may be relevant here, but as far as I could tell it was mentioned only in the informative annex.

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1 Answer

  1. Editorial Team

    Take a look at -ftrapv and -fwrapv:

    -ftrapv

    This option generates traps for signed overflow on addition, subtraction, multiplication operations.

    -fwrapv

    This option instructs the compiler to assume that signed arithmetic overflow of addition, subtraction and multiplication wraps around using twos-complement representation. This flag enables some optimizations and disables other. This option is enabled by default for the Java front-end, as required by the Java language specification.

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