std::numeric_limits<T>::is_modulo

static const bool is_modulo;

static constexpr bool is_modulo;

The value of std::numeric_limits<T>::is_modulo is true for all arithmetic types T that are possible to (until C++11)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 of max()-min()+1.

Standard specializations

Notes

Although the C++11 standard still says "On most machines, this is true for signed integers.", it is a defect and has been corrected. The exact wording changed from C++03 to C++11 in such a way that the true value is no longer compatible with undefined behavior on signed integer overflow. Because of that, the implementations that rely on signed overflow being undefined (for optimization opportunities) now set is_modulo to false for signed integers. See for example GCC PR 22200.

Example

#include <iostream>
#include <type_traits>
#include <limits>
 
template<class T>
typename std::enable_if<std::numeric_limits<T>::is_modulo>::type
    check_overflow()
{
    std::cout << "\nmax 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>();
    check_overflow<unsigned long>();
    // check_overflow<float>(); // compile-time error, not a modulo type
}

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

Defect reports

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

See also