const int double pointer
===========================

In this section, you are going to learn

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		What is ``const int **q;`` ?

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		What is ``const int *const *q;`` ?

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		What is ``const int *const *const q;`` ?

	* Inorder to answer above questions, let us remember a very simple rule

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		Anything after ``const`` keyword CAN NOT be changed

	* Is it that simple ?

		* Yes. Let us see how do we apply above rule to answer the questions


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                Topics in this section,

                        * :ref:`Example 1 : const int **q; <const_ptr_int_dp_ex_1>`
                        * :ref:`Example 2 : const int *const *q; <const_ptr_int_dp_ex_2>`
                        * :ref:`Example 3 : const int *const *const q; <const_ptr_int_dp_ex_3>`
                        * :ref:`Summary <const_ptr_int_dp_ex_4>`

.. _const_ptr_int_dp_ex_1:

.. tab-set::

    .. tab-item:: Example 1 :  const int \*\*q;

	* Step 1 : Consider the statement

	.. code-block:: c

		const int **q;

	* Step 2 : Remove all keywords after ``const``

	.. code-block:: c

		const **q;

	* Step 3 : Remove everything before ``const``

	.. code-block:: c

		const **q;

	* Step 4 : Remove assignment

	.. code-block:: c

		const **q;

.. tab-set::

    .. tab-item:: Example 1 : Snippet 1

	* Step 5 : Now apply the rule. Anything after ``const`` keyword CAN NOT be changed

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		* We see ``**q`` after ``const``
		* Means, ``**q`` CAN NOT be changed again in next line

	.. code-block:: c

	        int a = 5;
	        int *p; 
	        const int **q;

	        p = &a; 
        	q = &p; 
	        **q = 100; // --> This is invalid
.. tab-set::

    .. tab-item:: Example 1 : Snippet 2

	* Step 6 : Bonus point ! q, \*q, \*\*q are different

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		Means, ``q`` and ``*q`` can still be changed

	.. code-block:: c

	        int a = 5, b = 6;
	        int *x, *y; 
	        const int **q;

	        x = &a; 
        	q = &x;  // --> This is valid

	        y = &b; 
        	*q = y; // --> This is valid

		printf("**q = %d\n", **q); // --> prints 6

.. _const_ptr_int_dp_ex_2:

.. tab-set::

    .. tab-item:: Example 2 : const int \*const \*q;

	* There are two occurences of const keyword

	* Hence, let us apply the same rules two times

.. tab-set::

    .. tab-item:: 2.1 : Rules w.r.t first const

	* Step 1 : Consider the statement

	.. code-block:: c

		const int *const *q;

	* Step 2 : Remove all keywords after first const

	.. code-block:: c

		const **q;

	* Step 3 : Remove everything before first const

	.. code-block:: c

		const **q;

	* Step 4 : Remove assignment

	.. code-block:: c

		const **q;

	* Step 5 : Now apply the rule. Anything after const keyword CAN NOT be changed

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		\*\*q CAN NOT be changed

.. tab-set::

    .. tab-item:: 2.2 : Rules w.r.t second const

	* Step 1 : Consider the statement

	.. code-block:: c

		const int *const *q;

	* Step 2 : Remove all keywords after second const

	.. code-block:: c

		const int *const *q;

	* Step 3 : Remove everything before second const

	.. code-block:: c

		const *q;

	* Step 4 : Remove assignment

	.. code-block:: c

		const *q;

	* Step 5 : Now apply the rule. Anything after const keyword CAN NOT be changed

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		\*q CAN NOT be changed

.. tab-set::

    .. tab-item:: Summary of Example 2

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		* \*\*q, \*q CAN NOT be changed
		* q can be changed 

.. _const_ptr_int_dp_ex_3:

.. tab-set::

    .. tab-item:: Example 3 : const int \*const \*const q;

	* There are three occurences of const keyword

	* Hence, let us apply the same rules three times

.. tab-set::

    .. tab-item:: 3.1 : Rules w.r.t first const

	* Step 1 : Consider the statement

	.. code-block:: c

		const int *const *const q;

	* Step 2 : Remove all keywords after first const

	.. code-block:: c

		const **q;

	* Step 3 : Remove everything before first const

	.. code-block:: c

		const **q;

	* Step 4 : Remove assignment

	.. code-block:: c

		const **q;

	* Step 5 : Now apply the rule. Anything after const keyword CAN NOT be changed

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		* \*\*q CAN NOT be changed
.. tab-set::

    .. tab-item:: 3.2 : Rules w.r.t second const

	* Step 1 : Consider the statement

	.. code-block:: c

		const int *const *const q;

	* Step 2 : Remove all keywords after second const

	.. code-block:: c

		const int *const *q;

	* Step 3 : Remove everything before second const

	.. code-block:: c

		const *q;

	* Step 4 : Remove assignment

	.. code-block:: c

		const *q;

	* Step 5 : Now apply the rule. Anything after const keyword CAN NOT be changed

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		\*q CAN NOT be changed

.. tab-set::

    .. tab-item:: 3.3 : Rules w.r.t third const

	* Step 1 : Consider the statement

	.. code-block:: c

		const int *const *const q;

	* Step 2 : Remove all keywords after third const

	.. code-block:: c

		const int *const *const q;

	* Step 3 : Remove everything before third const

	.. code-block:: c

		const q;

	* Step 4 : Remove assignment

	.. code-block:: c

		const q;

	* Step 5 : Now apply the rule. Anything after const keyword CAN NOT be changed

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		* q CAN NOT be changed

.. tab-set::

    .. tab-item:: Summary of Example 3

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		\*\*q, \*q, q CAN NOT be changed

.. _const_ptr_int_dp_ex_4:

.. tab-set::

    .. tab-item:: Summary

	============================== ====================================================
	Statement                      Meaning
	============================== ====================================================
	const int \*\*q;	       * ``**q`` CAN NOT be changed again
				       * ``*q`` can be changed again
	                               * ``q`` can be changed again
	const int \*const \*q;         * ``**q`` CAN NOT be changed again
				       * ``*q`` CAN NOT be changed again
	                               * ``q`` can be changed again
	const int \*const \*const q;   * ``**q`` CAN NOT be changed again
				       * ``*q`` CAN NOT be changed again
				       * ``q`` CAN NOT be changed again
	============================== ====================================================

.. card:: See Also

        * Current Module

                * :doc:`../const_ptr`

        * Previous Module

                * :doc:`../../memcpy_ptr/memcpy_ptr`

        * Next Module

                * :doc:`../../void_ptr/void_ptr`

        * Other Modules

                * :doc:`../../variable_and_ptr/variable_and_ptr`
                * :doc:`../../array_n_ptrs/array_n_ptrs`
                * :doc:`../../malloc_ptr/malloc_ptr`
                * :doc:`../../typecasting_n_ptr/typecasting_n_ptr`
                * :doc:`../../funcs_n_ptrs/funcs_n_ptrs`
                * :doc:`../../array_of_ptr/array_of_ptr`
                * :doc:`../../ptr_to_array/ptr_to_array`
                * :doc:`../../function_ptr/function_ptr`
                * :doc:`../../pre_incr_ptr/pre_incr_ptr`
                * :doc:`../../post_incr_ptr/post_incr_ptr`
                * :doc:`../../pre_decr_ptr/pre_decr_ptr`
                * :doc:`../../post_decr_ptr/post_decr_ptr`