C Storage Classes Interview Questions

36. Define storage classes and what are the different types of storage classes in C?

A storage class defines the scope, visibility and life-time of variables. Refer For More C Storage Classes

• auto storage class
• static storage class
• register storage class
• extern storage class

37. Define auto storage class?

• All variables declared inside a function without any storage classes keyword is considered as auto storage class by default.
• In auto storage class a memory is allocated automatically to the variables when the function is called and deallocates automatically when the function exits.
• Variables under auto storage classes are local to the block or function. So, it is also called as local variables.
• The keyword auto is rarely used because all uninitialized variables are said to have auto storage classes.

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38. Define static storage class?

• A static variable is a variable that tells the compiler to retain the value until the program terminates.
• They are created once when the function is called, even though the function gets repeated it retains the same value and exists until the program terminates.
• The default value of static variable is zero(0).
• The keyword for a variable to declared under static storage class is static

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39. Define register storage class?

• Register variables are similar to auto variables. The only difference is register variables are stored in CPU register instead of memory.
• Register variables are faster than normal variables. Mostly programmers uses register to store frequently used variables.
• Programmers can store only few variables in the CPU register because size of register is less.
• The keyword for a variable to declared under register storage class is register.

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40. Define extern storage class?

• extern variable is a programmer's shorthand to represent external variable.
• extern variables are also known as global variables because extern variables are declared above the main function.
• So, the variables can be accessed by any function.
• We can also access extern variables of one file to another file. But make sure both files are in same folder. The keyword for a variable to declared under extern storage class is extern.

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