Using register variables in recursion?

Question

    #include <stdio.h>

    void main()

    {

        register int x = 0;

        if (x < 2)

        {

            x++;

            main();

        }

    }

Output:

segmentation fault

Why I am getting segmentation fault?

Answer 1

Register has nothing to do with this error. It is just a type of storage class.

Even without register it shows core dump.

The reason for the core dump is stack overflow becaz of recursion.

Try by using printf("%d",x) after x++ and before main();

if (x < 2)

    {

        x++;
        printf("%d",x);

        main();

    }

The reason for stack gets overflow is every time you called main() in recursion the x re initialized to 0, thus always satisfies the condition if(x < 2) and results in stack overflow.

Try to use static storage class to avoid this error.

Answer 2

Because 'register' is an advisory to the compiler, which compilers are free to ignore. They say "put this variable in a register, please" but it doesn't change the scope of x in your code. Which means main will be called, and then create a local variable called x reserving space on the stack, initialise it to zero, etc, etc, etc.