What is the default value of extern variable in C?

What is the default value of extern variable in C?

The default value of an `extern` variable in C is *undefined*. Unlike global variables, which are automatically initialized with a default value of zero, extern variables do not have a defined initial value. It is important to explicitly initialize extern variables before using them to avoid potential issues and ensure the desired behavior.

Frequently Asked Questions:

1. What is an extern variable in C?

An extern variable is a global variable that is declared in one file but can be accessed by other files in a program.

2. Do extern variables have a storage location?

Yes, extern variables have a storage location, but their value is determined by the definition in another file.

3. Can extern variables be initialized?

Extern variables can be initialized, but it is recommended to initialize them explicitly to avoid potential issues.

4. What happens if an extern variable is not explicitly initialized?

If an extern variable is not explicitly initialized, it will have an undefined value, which can lead to unexpected behavior.

5. How can I initialize an extern variable?

Extern variables can be initialized by assigning them a value in the file where they are defined, or they can be initialized using an assignment statement in a function.

6. Can I define an extern variable with the same name in multiple files?

Yes, it is possible to define an extern variable with the same name in multiple files, but it can lead to conflicts and should be avoided.

7. Can I initialize an extern variable in multiple files?

No, an extern variable can only be initialized once in a program. Multiple initializations can lead to linker errors.

8. Can I change the value of an extern variable in different files?

Yes, the value of an extern variable can be changed in different files, as long as they are all referring to the same extern variable.

9. Are extern variables affected by scope rules?

Extern variables have global scope, meaning they can be accessed from any part of a program, but they can still be limited by other scope rules if declared within a particular block.

10. Can I use an extern variable without a declaration?

No, an extern variable must be declared in a file before it is used. The actual definition can be in another file.

11. What is the purpose of using extern variables?

Extern variables are commonly used to share data between multiple files of a program, allowing them to communicate and exchange information.

12. Can I declare an extern variable without defining it anywhere?

Yes, it is possible to declare an extern variable without defining it anywhere, but the variable must be defined in another file for the program to link successfully.

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