Most new C++ programming students are taught to add “using namespace std” in the global scope after introducing the headers needed for their programs to compile successfully. As a result, students grow accustomed to engaging in this practice without realizing how bad it is. Including ‘using namespace std’ in the global scope is bad practice. Some programmers are simply unaware of this, while others find it less demanding to add that statement in the global scope.

With online learning becoming increasingly prevalent, especially for aspiring programmers, it’s easy to learn bad coding practices because there’s no way to understand the author’s skill level. In other instances, people do know what to do but prefer the easy option. However, there are many downsides of adding this simple statement while coding. It’s worth finding out why so that you do not end up like me and run into a more experienced supervisor who frowns at its use.

This article provides information about “using namespace std” and why it is a bad idea to add it in the global scope. It also proposes better alternatives that can be adopted in its stead.

What is using namespace std?

I remember rolling my eyes while reading a blog post some time ago after seeing someone write code that read like this:

std:cout << “you” << std:endl << std::lcm(2, 2) << std::gcd(3, 7) …ad infinitum;

In my head, I was thinking “Pftt! I mean who does this? I hope you know that you can simply write ‘using namespace std’ instead of engaging in this tedious, repetitive, boring task.” I probably also laughed at the ridiculousness of it. Well, who would have thought that I’d be here writing an article about why you should try to write code in the same way? Definitely not me.

So, what is ‘using namespace std?’ Someone less experienced (like the version of me that existed two weeks ago) might define it as the statement one must add to their header file if they want to avoid encountering certain really nasty, headache-inducing errors. On the other hand, a more experienced programmer might begin to break it down to aid understanding like this: “first, std is short for standard, and the keyword ‘using’ specifies that the standard namespace should be used whenever possible. The keyword ‘namespace’ helps distinguish between different identifiers, and its use is supposed to prevent name collision. Hence, it is important to make use of namespaces in your program so that you don’t run into compile errors. With ‘using namespace std’ however, if an identifier is not found in the global scope the compiler will look in the standard library scope instead. This has its downsides and should be avoided at all costs.”

In short, it will be wise to listen to the second, a more experienced programmer who has his head screwed on straight.

Why you should avoid using namespace std in the global scope?

When ‘using namespace std’ is added to your code, the compiler will look for identifiers in the std:: namespace if it can’t find them in the global namespace. The maintainability of the program will decrease after making this inclusion since the whole content in the directive might not be needed and it can lead to confusion. This action is referred to as namespace pollution. Additionally, if anyone chooses to make use of the code you have written by including your header into their program, they will also inherit this ‘using’ behaviour, which is very likely not what they desire and may cause code breakages.

One key consequence of making this choice is that you might encounter name collisions in your program. To put it simply, name collisions occur when compilers can’t differentiate between identifiers. An example is when an identifier is added more than once. Let’s assume you write this code:

namespace std1  
	int someFunction(int) 
	 
		/* Does something */ 
	 

And you have another namespace written by someone else that also has the same function name. Somehow this code is imported into your program:

namespace std2  
	int someFunction(long int) 
	
		/* Does something different*/ 
	 

Finally, you add the following code to call the function.

using namespace std1; 
using namespace std2; 

int main() 

 	someFunction(6); 

This will inadvertently lead to an issue because one function might be used in place of another. To make things worse, the compiler will not warn you, and it will be difficult for you to locate what the issue is. Talk about inducing headaches! Thus, it is better to make the effort to avoid this confusion. The better thing to do will be to specify which function is being referred to by writing std1::someFunction or std2::someFunction.

Better Alternatives for ‘using namespace std’

In this section, some alternatives that can be used in place of ‘using namespace std’ will be discussed. Embarcardero’s C++Builder will be used to show the different alternatives.

Instead of writing code in this manner:

namespace std 1

You can add only the directives needed in the local scope by doing this:

namespace std 2

Another common way is shown in the snippet below. Although it is a bit tedious, it is still a better way of writing code, and your supervisor will appreciate you for doing so:

namespace std 3

Conclusion

In conclusion, you should make an effort to use one of the methods shared above. It will not only prevent you from encountering name collisions and contributing to namespace pollution; it will also make you a better programmer. For some final parting words:

namespace std 4

This post is sponsored by Embarcadero, creator of the C++Builder, the powerful C++ IDE for multi-platform development focusing on database access and excellent UI design for all your platforms.

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