使用命名空间std和模板类(using namespace std and Template Classes)

 我现在可以看到为什么包含这种做法不好 
 
using namespace std;
 
 在项目的头文件中。 我听说在私有.cpp函数定义文件中包含这个指令并不是一个问题，因为它们通常不直接包含在main（）中。 模板化类是否存在异常，通常必须包含.cpp定义文件才能正确编译和运行（除非直接在头文件中包含定义）？ 
 
 那么，一般规则是： 
 
 1）不要在头文件中使用namespace std。 2）可以在私有.cpp定义文件中使用它，除非定义是用于模板化类。 

I can now see why it would be bad practice to include 
 
using namespace std;
 
in header files for a project. I have heard that including this directive in private .cpp function definition files is not so much of a problem, since they are usually not directly included in main(). Is there an exception here for templated classes, which usually have to include the .cpp definition files to compile and run correctly (unless you include the definitions directly in the header file)?
 
So, would the general rules be:
 
1) Don't use using namespace std in header files. 2 ) It's okay to use it in private .cpp definition files, unless the definitions are for templated classes.

原文：https://stackoverflow.com/questions/20573994