Why are some things left undefined in C++?
Because machines differ and because C left many things undefined. For details, including definitions of the terms “undefined”, “unspecified”, “implementation defined”, and “well-formed”; see the ISO C++ standard. Note that the meaning of those terms differ from their definition of the ISO C standard and from some common usage. You can get wonderfully confused discussions when people don’t realize that not everybody share definitions. This is a correct, if unsatisfactory, answer. Like C, C++ is meant to exploit hardware directly and efficiently. This implies that C++ must deal with hardware entities such as bits, bytes, words, addresses, integer computations, and floating-point computations the way they are on a given machine, rather than how we might like them to be. Note that many “things” that people refer to as “undefined” are in fact “implementation defined”, so that we can write perfectly specified code as long as we know which machine we are running on. Sizes of integers and the
