为什么是“using namespace std”认为坏做法？ [英] Why is "using namespace std" considered bad practice?

问题描述

我已经在其他人多次告诉我的老师的建议行使使用命名空间std 在代码是错误的。因此，我们应该使用 std :: cout 和 std :: cin 。

I've been told by others on numerous occasions that my teacher's advice of exercising using namespace std in code was wrong. Hence, we should use std::cout and std::cin.

为什么使用命名空间std 被视为不良做法？是真的那么低效或风险声明不明确的变量（变量与 std 命名空间中的函数共享相同的名称）？或者，这是否会影响性能？

Why is using namespace std considered bad practice? Is it really that inefficient or risk declaring ambiguous variables (variables that share the same name as a function in std namespace)? Or, does this impact performance?

推荐答案

这与性能无关。但是考虑这样：你使用两个名为Foo和Bar的库：

This is not related to performance at all. But consider this: you are using two libraries called Foo and Bar:

using namespace foo;
using namespace bar;

一切正常，你可以调用 Blah c>从Foo和 Quux（）从Bar没有问题。但有一天你升级到新版本的Foo 2.0，现在提供了一个名为 Quux（）的函数。现在你有一个冲突：Foo 2.0和Bar导入 Quux（）到你的全局命名空间。

Everything works fine, you can call Blah() from Foo and Quux() from Bar without problems. But one day you upgrade to a new version of Foo 2.0, which now offers a function called Quux(). Now you've got a conflict: Both Foo 2.0 and Bar import Quux() into your global namespace. This is going to take some effort to fix, especially if the function parameters happen to match.

如果你使用了 foo :: Blah（）函数， 和 bar :: Quux（），然后介绍 foo :: Quux >将是一个非事件。

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

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