c++ - 为什么“使用命名空间标准”被认为是不好的做法？(Why is “using namespace std;” considered bad practice?)

Question

I've been told by others that writing using namespace std;

(其他人告诉我， using namespace std;编写using namespace std;)

in code is wrong, and that I should use std::cout and std::cin directly instead.

(在代码中是错误的，我应该直接使用std::cout和std::cin代替。)

Why is using namespace std;

(为什么using namespace std;)

considered a bad practice?

(认为是不好的做法？)

Is it inefficient or does it risk declaring ambiguous variables (variables that share the same name as a function in std namespace)?

(是效率低下还是冒着声明模棱两可的变量（与std名称空间中的函数具有相同名称的变量）的风险？)

Does it impact performance?

(它会影响性能吗？)

  ask by akbiggs translate from so

Answer 1

This is not related to performance at all.

(这根本与性能无关。)

But consider this: you are using two libraries called Foo and Bar:

(但是考虑一下：您正在使用两个名为Foo和Bar的库：)

using namespace foo;
using namespace bar;

Everything works fine, and you can call Blah() from Foo and Quux() from Bar without problems.

(一切正常，您可以从Foo调用Blah()并从Bar调用Quux()而不出现问题。)

But one day you upgrade to a new version of Foo 2.0, which now offers a function called Quux() .

(但是有一天，您将升级到Foo 2.0的新版本，该版本现在提供了称为Quux()的功能。)

Now you've got a conflict: Both Foo 2.0 and Bar import Quux() into your global namespace.

(现在您有一个冲突：Foo 2.0和Bar都将Quux()导入到全局名称空间中。)

This is going to take some effort to fix, especially if the function parameters happen to match.

(这将需要花费一些时间来解决，特别是在功能参数碰巧匹配的情况下。)

If you had used foo::Blah() and bar::Quux() , then the introduction of foo::Quux() would have been a non-event.

(如果您使用过foo::Blah()和bar::Quux() ，那么foo::Quux()的引入将是非事件。)