Limitation of “using” Keyword

The “using” keyword can be very useful, but it can also lead to problems if you’re not careful.

you need to be careful about using it with large codebases. The reason for this is that it can sometimes lead to name collisions.
You can only have one namespace in each file.
If you have multiple namespaces in a file, you have to fully qualify the names of any type in a namespace other than the one you are currently in.
You cannot use the using keyword to make types in the global namespace visible.
You cannot use the using keyword to make types in the System namespace visible.
You cannot use the using keyword to make types in a parent namespace visible.
You cannot use the using keyword to make static classes visible.

Note:

Imagine you have a codebase that includes both the “std” and “mynamespace” namespaces. If you use the “using” keyword to bring everything in both namespaces into your code, you might end up with two objects with the same name. This can cause compile-time errors or, worse, unexpected behavior at runtime.

To avoid these problems, it’s best to be explicit about which namespaces you’re using.

Example: if you only want to use the “std” namespace, you should write your code like this: using namespace std;

And if you only want to use the “mynamespace” namespace, you should write your code like this: using namespace mynamespace; This may seem like a lot of extra work, but it’s worth it to avoid problems down the road. The “using” keyword is a powerful tool that allows you to specify the use of a particular entity in your program. In particular, it is often used to specify the use of a namespace, class, or function.

Example 1:

C++

// C++ Program to implement
// "using" keyword
#include <iostream>
using namespace std;
 
int main()
{
    cout << "Hello, world!" << endl;
    return 0;
}

Output

Hello, world!

In this code, the “using” keyword is used to specify the use of the “cout” object from the “std” namespace. Without the “using” keyword, the code would not compile.

The “using” keyword can also be used to specify the use of a particular function or class.

Example 2:

C++

// C++ Program to implement
// "using" keyword
#include <iostream>
#include <string>
 
using std::cout;
using std::endl;
using std::string;
 
int main()
{
 
    string s = "Hello, world!";
    cout << s << endl;
    return 0;
}

Output

Hello, world!

In this code, the “using” keyword is used to specify the use of the “string” and “cout” objects from the “std” namespace. Without the “using” keyword, the code would not compile.

Using Keyword in C++ STL

The using keyword in C++ is a tool that allows developers to specify the use of a particular namespace. This is especially useful when working with large codebases or libraries where there may be many different namespaces in use. The using keyword can be used to specify the use of a single namespace, or multiple namespaces can be listed using the using keyword.

When using the using keyword, it is important to keep in mind that the specified namespace will take precedence over any other namespace that is in scope. This can lead to unexpected results if the code is not well-organized. For this reason, it is generally considered good practice to use the using keyword sparingly and only when absolutely necessary.

In addition to the using keyword, C++ also provides the using namespace directive. This directive can be used to specify the use of all namespaces in a particular library or codebase. The using namespace directive should be used with caution, as it can make code difficult to read and maintain. This can be especially useful when working with large codebases or when you want to make sure that your code will run in a specific environment.

Tags:

#STL #Technical Scripter 2022 #C++ #Technical Scripter #CPP #STL

Forms of “using” Keyword

Limitation of “using” Keyword

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Using Keyword in C++ STL

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