在哪里放使用namespace std; [英] where to put using namespace std;

问题描述

我想知道在中使用namespace std; 。我在 int main（）{} 中看到了一个使用的命名空间std; 的代码， #include< iostream> 。

I'm wondering where to put using namespace std;. I saw a code with the using namespace std; in the int main(){} but I was putting it after #include <iostream>. Where should I put it and does it make any difference where I put it?

推荐答案

这会使巨大

如果你把它放在一个函数中，那么它只适用于该函数。

If you put it inside a function, then it only applies in that function.

如果将它放在全局范围内的函数之外，那么它会应用于该点之后的所有内容。

If you put it outside a function in global scope then it applies to everything after that point.

如果将它放在全局范围的函数之外

If you put it outside a function in global scope in a header file then it will even apply to ever file that includes that header.

一般来说，在标题中使用它在全局范围是非常糟糕的做法，而半不良实践在全局范围内使用它，因为在 Unity builds 中，标题和来源之间的区别文件是模糊的。

Generally, it's very bad practice to use it at global scope in a header, and semi bad practice to use it in global scope at all since in Unity builds, the distinction between headers and source files is blurred.

你最好只是在你需要的函数中使用它，或者甚至不使用它，只是前缀标准库函数/类与 std :: 。

You would be best to just use it in the functions that you need it, or even not use it at all and just prefix standard library functions/classes with std::.

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