c++ - Generate next largest or smallest representable floating point number without bit twiddling

Question

Given an arbitrary finite floating point number, is there a way to determine what the next representable floating point number? For example, given 1.0f, by definition the next largest representable number is 1.0f + std::numeric_limits<float>::epsilon(). Is there a way to synthesize an epsilon for any value - not just 1.0f - without resorting to bit twiddling and/or explicit knowledge of how the machine represents floating point values?

Answer 1

In C++11, you use std::nextafter(). Lacking that, on a C99 system, you use nextafterf, nextafter, or nextafterl from the C math library (for types float, double, and long double, respectively).