As an illustration of how much code gets included (on macOS Sierra): $ echo "#include <iostream>" > foo.cpp $ g++ -E foo.cpp | wc 37799 104779 12808

As an illustration of how much code gets included (on macOS Sierra): $ echo "#include <iostream>" > foo.cpp $ g++ -E foo.cpp | wc 37799 104779 1280834 Including just iostream in a file means the compiler has to process 37799 (!) lines. For comparison, a C file including stdio: $ echo "#include <stdio.h>" | gcc -E - | wc 456 1638 20880 That still looks bloated to me, but is about 60x times fewer bytes.