Usage of pointers [3]

 

The following describes the relationship between pointers and arrays.

 

Pointer to a one-dimensional array

 

Pointer to a multi-dimensional array

 

Pointer to a string

 

 

 

 

 

1. Definition of pointer variables pointing to array elements: type * pointer variable name

 

Example: int * p;

 

2. Meaning of array name: array name indicates the first address of the array.

 

3. assign a value to the pointer variable of the array element: pointer variable = address of an array element (usually the first address)

 

Example: int a [10], * p;

 

P = a; or p = & a [0];

 

Figure:

 

 

 

Addition and subtraction of pointer to array

 

P ++; // p pointer moves p to the type byte, p points to the int type array, so p moves two bytes to a [1]

 

There are two methods to reference an array:

 

1. subscript method: for example, a [I]

 

2. pointer method: for example, * (a + I) or * (p + I)

 

 

If an array and pointer are defined as int a [5], * p =;

 

Subscript Method: a [0] a [1] a [2] a [3] a [4]

 

Pointer method: * p * (p + 1) * (p + 2) * (p + 3) * (p + 4)

 

P [0] p [1] p [2] p [3] p [4]

 

 

* A * (a + 1) * (a + 2) * (a + 3) * (a + 4)

 

Calculate the address of the array element using the array name to find the element value.

 

Main ()

 

{

 

Int a [10]; int I;

 

For (I = 0; I <10; I ++)

 

 

Scanf ("% d", & a [I]);

 

Printf ("\ n ");

 

For (I = 0; I <10; I ++)

 

Printf ("% d", * (a + I ));

 

}

 

Use Pointer variables to point to array elements:

 

Main ()

 

{

 

Int a [10];

 

Int * p, I;

 

For (I = 0; I <10; I ++)

 

Scanf ("% d", p ++ );

 

Printf ("\ n ");

 

For (p = a; p <(a + 10); p ++)

 

Printf ("% d", * p );

 

 

}

 

Note: p ++ is valid, but a ++ is invalid (a is the array name, representing the first address of the array, which is a constant address)

 

Pay attention to the current value of the pointer variable.

 

 

 

 

P ++; (or p + = 1 ;)

 

P points to the next element, that is, a [1].

 

 

 

 

X = * p ++; // not recommended

 

* Similar to ++, it is equivalent to calculating * p first, assigning a [0] to x, and then ++

 

 

 

 

* (P ++) and * (++ p)

 

* (P ++) is to first take the value of * p, and then make p + 1;

 

* (++ P) adds 1 to p first, and then obtains the value of * p.

 

 

 

 

(* P) ++;

 

Indicates that the element value pointed to by p is incremented by 1 (that is, a [0] ++), rather than the pointer value plus 1.

 

Example:

 

Main ()

 

{

 

Int a [3], * p =;

 

A [0] = 10; a [1] = 20; a [2] = 30;

 

Printf ("% d/t", * p ++ );

 

Printf ("% d \ n", * ++ p );

 

 

}

 

Output result: 10 30

 

Main ()

 

{

 

Int a [] = {1, 2, 3, 4, 5 };

 

Int * p = a + 3;

 

Printf ("% d, % d, % d \ n", * p, * (p + 1), * p + 3 );

 

 

}

 

Result: 4, 5, 7

 

Multi-dimensional array pointer

 

1. The definition reference format is similar to the pointer to a one-dimensional array.

 

Example: int a [3] [4], * p

 

P = & a [2] [3];

 

2. Column and column address Representation

 

If defined: int a [3] [4];

 

The number in the table indicates the address value of each element.

 

 

Pointer and string

 

1. String Representation

 

Use a character array: char string [] = "I Love China! ";

 

Use a character pointer: the definition of a character pointer variable: char * p;

 

Value assignment: pointer = address of a character in the string

 

 

Char * s = "I Love China! "; // Initialize s

 

 

The string ends with a/0 identifier, so the actual length is the string length + 1.