Smallest expressible value above given value

Question

Given a variable defined as

T x;

where T is a generic arithmetic type (i.e. such that std::is_arithmetic<T>::value), is there a simple expression (e.g something from std::numeric_limits) that evaluates to the lowest value y expressible in T such that y > x?

(i.e. a kind of generalized increment..)

Answer 1

You can use std::nextafter.

Note that here I use std::numeric_limits<Floating>::max(), if you want meaningful behavior for infinities, you might want to modify the code.

#include <iostream>
#include <limits>
#include <cmath>
#include <type_traits>
#include <iomanip>

template <typename Floating,
    std::enable_if_t<std::is_arithmetic_v<Floating> && !std::is_integral_v<Floating>, bool> = false>
Floating generic_next_val(Floating val) {
    return std::nextafter(val, std::numeric_limits<Floating>::max());
}

template <typename Integral,
    std::enable_if_t<std::is_arithmetic_v<Integral> && std::is_integral_v<Integral>, int> = 0>
Integral generic_next_val(Integral val) {
    return static_cast<Integral>(val + static_cast<Integral>(1));
}

int main() {
    int a = 1;
    float f = 0.0f;
    std::cout << std::setprecision(20) << generic_next_val(f) << " " << generic_next_val(a) << std::endl;
    return 0;
}