Two-dimensional array, pointer array and array pointer

Two-dimensional array, pointer array and array pointer

Http://www.cnblogs.com/birduu/archive/2013/04/04/2999185.html

I. pointer array and two-dimensional array
Let's define a struct pointer array P: char * P [3]; The Memory diagram after definition is as follows:

For the two-dimensional array char birduu [3] [16] = {"birduu.com", "course textbook", "free, the value of birduu [0] is the first address of the string "birduu.com". That is to say, birduu [0] can be interpreted as a struct pointer pointing to the first element 'B' of the string "birduu.com. For pointer array p, p [0] is a struct pointer, and the base type of P [0] Is struct. It is the same as the base type of birduu [0, the value can be assigned as follows: P [0] = birduu [0];
In this case, P [0] points to the string "birduu.com ". Similarly, execute P [1] = birduu [1]; P [2] = birduu [2]; then P [1] points to the string "course textbook ", P [2] points to the string "free ". The memory is as follows:

Then, you can use P to operate the two-dimensional array birduu, as shown in the example column.
Note that p is a pointer array, and the array name cannot be assigned values. Do not write it as: P = birduu;

Program instance:

# Include <stdio. h>
Void main ()
{
Char birduu [3] [16] = {"birduu.com", "course textbook", "free "};
Char * P [3];
P [0] = birduu [0];
P [1] = birduu [1];
P [2] = birduu [2];

Printf ("% s \ n", P [0]);
Printf ("% C \ n", P [0] [1]);
Printf ("% C \ n", * (p + 2) + 3 ));
}

Output: birduu.com
I
E

 

2. array pointer and two-dimensional array

An array pointer is a pointer to an array. First, define an array pointer Variable P: Char (* P) [16];
* P indicates that p is a pointer variable. Char [16] indicates that the base type of P is a one-dimensional array containing 16 struct elements, that is to say, P can point to a one-dimensional array containing 16 struct elements.
Next let's take a look at how to use an array pointer to operate a two-dimensional array. As we mentioned in the http://birduu.com/260.html section, we can understand the two-dimensional array name as a pointer variable pointing to the first row array element. Two-dimensional array
Char birduu [3] [16] = {"birduu.com", "course textbook", "free"}; the first row array element is a one-dimensional array containing 16 struct elements, therefore, we can understand the two-dimensional array name birduu as a pointer to the one-dimensional array birduu [0]. Its base type is a one-dimensional array containing 16 struct elements, the value of birduu is the address of the one-dimensional array birduu [0.
From the above analysis, we can see that the base types of the pointers birduu and P are the same, so we can assign a value like this: P = birduu; then P points to birduu [0], because the base type of P is a one-dimensional array containing 16 struct elements, the pointer (p + 1) points to birduu [1], and the pointer (p + 2) points to birduu [2]. The memory is as follows:

 

Since then, P can be used to operate the two-dimensional array birduu. Since P is a pointer variable, it can reference array elements regardless of the pointer, subscript, or hybrid method.

Program instance:

# Include <stdio. h>

Void main ()
{
Char birduu [3] [16] = {"birduu.com", "course textbook", "free "};
Char (* P) [16];

P = birduu;

Printf ("% s \ n", P [0]);
Printf ("% C \ n", P [0] [1]);
Printf ("% C \ n", * (p + 2) + 3 ));
Printf ("% C \ n", * (p [2] + 3 ));
Printf ("% s \ n", * (p + 1 ));
}

Output:

Birduu.com
I
E
E
Course textbook