<cstdint> vs std::size_t types

Question

From the peeks I've made into boost and libstdc++, the libraries usually make use of std::size_t and std::ssize_t whenever the upper/lower limit of an unsigned/signed index is not known in advance. My question is: Why not rather use uintmax_t from <cstdint> instead of std::size_t and intmax_t instead of std::ssize_t?

Answer 1

The former are part of the C++ standard, the latter are not. More precisely, the cstdint header was only recently introduced (in C++11). The reason for this is that stdint.h itself is part of C99, which is newer than C++98.