Can you use namespace in header file?

Can you use namespace in header file?

9 Answers. You should definitely NOT use using namespace in headers for precisely the reason you say, that it can unexpectedly change the meaning of code in any other files that include that header. There’s no way to undo a using namespace which is another reason it’s so dangerous.

Is using namespace std a header file?

And I’m gathering that applying “using namespace std;” in a header file is a no-no, and that to fully qualify is the “better” practice; such as std::cout << stuff << endl; It is my understanding that in order to use a string, it must have the std namespace.

Why should you never place a using namespace directive inside of a header file?

However you’ll virtually never see a using directive in a header file (at least not outside of scope). The reason is that using directive eliminate the protection of that particular namespace, and the effect last until the end of current compilation unit.

Where should I put using namespace?

Putting it above main in the file scope is fine if you know that no conflicts will arise, but even that may cause problems with other imported types and is generally to be avoided in moderately sized projects.

Why is using namespace std not working?

Why “using namespace std” is considered bad practice in C++ So they created a namespace, std to contain this change. While this practice is okay for example code, pulling in the entire std namespace into the global namespace is not good as it defeats the purpose of namespaces and can lead to name collisions.

What should be in a C++ header file?

To minimize the potential for errors, C++ has adopted the convention of using header files to contain declarations. You make the declarations in a header file, then use the #include directive in every . cpp file or other header file that requires that declaration.

Why is using namespace std bad?

Do not use namespace using directives use using declarations?

Using-directives are subtler than using-declarations. But the good news is that you should never use them! Seriously, don’t ever write using namespace Whatever ; and then you won’t have any trouble with them.

What is the point of header files?

The primary purpose of a header file is to propagate declarations to code files. Header files allow us to put declarations in one location and then import them wherever we need them. This can save a lot of typing in multi-file programs.

Do you write namespace before a header in C + +?

Item 59 in Sutter and Alexandrescu’s “C++ Coding Standards: 101 Rules, Guidelines, and Best Practices”: 59. Don’t write namespace usings in a header file or before an #include. Namespace using s are for your convenience, not for you to inflict on others: Never write a using declaration or a using directive before an #include directive.

What’s the difference between a header file and a source file?

A header file is a guest in one or more source files. A header file that includes using directives and declarations brings its rowdy buddies over too. A using declaration brings in one buddy. A using directive brings in all the buddies in the namespace. Your teachers’ use of using namespace std; is a using directive.

Is there way to undo using namespace in headers?

There’s no way to undo a using namespace which is another reason it’s so dangerous. I typically just use grep or the like to make sure that using namespace isn’t being called out in headers rather than trying anything more complicated. Probably static code checkers flag this too.

When to use fully qualified name in header file?

Code in header files should always use the fully qualified namespace name. The following example shows a namespace declaration and three ways that code outside the namespace can accesses their members. Use the fully qualified name: Use a using declaration to bring one identifier into scope: