Why are bitwise shifts (<< and>>) used for cout and cin?

Question

Question is in the title really; I\'m sure there is something logical, but for now I\'m stumped!

Answer 1

Because they had more or less a reasonable precedence and looked good. In C++ you cannot create new operators or change their precedence or grouping rules, you can only overload existing ones and changing what they actually do.

The choice of << and >> has some unfortunate side effect because it's somehow pushing the idea that the output will be done respecting the order. While this is true for the actual output thanks to a clever chaining trick it's however false for the computations involved and this is very often surprising.

To be more specific writing

std::cout << foo() << bar() << std::eol;

does NOT imply that foo will be called before bar.

EDIT

With C++17 the sequence problem has been "fixed". Now the order of evaluation is specified to be left-to-right for << and >> operators. There are still places in C++ where the order of evaluation is unspecified (or even non-existing meaning that evaluation can be interleaved) but a few common cases now behave in a predictable and portable way see this answer .