std 代表什么？

Question

I understand that if there is not using namespace std , and you want to write a cout , you need to have a std::cout . What does the std represents? Why is std widely used ( std::vector , std::cout , std::cin )?

Answer 1

std stands for "standard".

The reason why so much standard stuff goes in the std namespace is simple: Before namespaces, different code written by different people would often use the same name and cause a conflict. For example, my drink dispenser program from 1994 might have a class ofstream which is an orange fanta stream. When a new version of C++ came along and added ofstream which was an output file stream, my program wouldn't compile any more, or it'd crash.

Okay, orange-fanta-stream is silly, but major operating systems do have C functions called open , close , and index . I'm sure many people have tried to make global variables called open , and then their programs have crashed.

In C++, all the new C++ standard stuff is inside std:: , so as long I don't call something in my program std , they can add new stuff inside std:: and it definitely won't cause this problem. Unfortunately all the stuff that C++ inherits from C is outside std:: , so you still can't make a global variable called open (on Linux), but at least it's a start.

Answer 2

It's a namespace reserved for the C++ standard library.

A good choice historically: any token starting with std is reserved in C. So that meant that early C++ compilers would not break existing C code. Of course the languages have diverged since then. Etymologically, std is an abbreviation for standard.