The value ofstd::numeric_limits<T>::is_modulo istrue for all arithmetic typesT that handle overflows with modulo arithmetic, that is, if the result of addition, subtraction, multiplication, or division of this type would fall outside the range[min(), max()], the value returned by such operation differs from the expected value by a multiple ofmax()- min()+1.

is_modulo isfalse for signed integer types, unless the implementation defines signed integer overflow to wrap.

[edit]Standard specializations

[edit]Notes

The standard said "On most machines, this istrue for signed integers." before the resolution ofLWG issue 2422. SeeGCC PR 22200 for a related discussion.

[edit]Example

#include <iostream>#include <type_traits>#include <limits> template<class T>typenamestd::enable_if<std::numeric_limits<T>::is_modulo>::type    check_overflow(){std::cout<<"max value is "<<std::numeric_limits<T>::max()<<'\n'<<"min value is "<<std::numeric_limits<T>::min()<<'\n'<<"max value + 1 is "<<std::numeric_limits<T>::max()+1<<'\n';} int main(){    check_overflow<int>();std::cout<<'\n';    check_overflow<unsignedlong>();//  check_overflow<float>(); // compile-time error, not a modulo type}

max value is 2147483647min value is -2147483648max value + 1 is -2147483648 max value is 18446744073709551615min value is 0max value + 1 is 0

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

1. ↑The definition is "adding two positive numbers can have a result that wraps around to a third number that is less". It has the following problems:
   • It does not define the wrapped value.
   • It does not state whether result is repeatable.
   • It does not require that doing addition, subtraction and other operations on all values have defined behavior.

[edit]See also

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