Auto Storage Class in C (Keyword)

January 17, 2023

Auto Storage Class in C

Auto is default storage class for all variables declared inside a function or block. So, we rarely write auto of any keyword in C.

Auto variables are only accessible within the block or function in which they were declared (which defines their scope). In the parent block or function where the auto variable was declared, these can be accessed within nested blocks.

However, using the idea of pointers presented here, they can also be accessed outside of their intended use by referring to the precise position in memory where the variables are stored.

Auto storage class

The automatic storage class includes variables defined within functions or blocks with the auto specifier.
If no storage class is specified, all variables defined within a function or block are automatically stored under that class.
The block in which they are defined is local to variables with automatic storage classes.
On leaving the block where they are defined, variables are destroyed.
Any garbage value is the default value for the variables in the automatic storage class.
The default storage class is called auto.

Tokens in C

Bitwise Operators in C

Conditional statement Program in C

Switch case program in C

function pointer in C

Working of the Code

In this code auto int i is defined at different stages with different scopes.
Each time auto int i is defined, it’s value will be printed only in that particular scope only.
First of all auto int i = 3 will be printed, then it’s scope will end.
Then auto int i = 2 will be printed, and then it’s scope will end.
At the end auto int i = 1 will be printed.

Run

#include<stdio.h>
int main()
{
    auto int i = 1;
    {
        auto int i = 2;
        {
            auto int i = 3;
            {
                printf("%d ",i);
            }
        }
        printf("%d ",i);
    }
    printf("%d ",i);
    return 0;
}

Output

 3 2 1

Now we will write above code without using auto keyword

Without using auto keyword still the output of the program will be same.
First of all int i = 3 will be printed.
Then int i = 2 will be printed.
At the end int i = 1 will be printed.

Run

#include<stdio.h> 
int main()
{
    int i = 1;
    {
        int i = 2;
        {
            int i = 3;
            {
                printf("%d ",i);
            }
        }
        printf("%d ",i);
    }
    printf("%d ",i);
    return 0;
}

Output

3 2 1

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Auto Storage Class in C (Keyword)

Auto Storage Class in C

Auto storage class

Working of the Code

Output

Now we will write above code without using auto keyword

Output

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