C Language -- pointer, -- pointer

C Language -- pointer, -- pointer
I. pointer 1. pointer declaration format

1> Format: variable type * variable name. For example, char * p defines a pointer Variable p, which can only store addresses.

* Remember * it's not a pointer variable name, it's just a pointer sign

2> role: the pointer acts as a storage address and accesses the corresponding bucket based on the address value.

3> example

1 int main () 2 {3 int a = 90; 4 int * p; 5 p = & a; 6 return 0; 7}Pointer code

* Representation of code in memory

* Note: ① int * p can only point to int type data. ② the pointer variable is initialized. Do not use it to indirectly access its bucket. ③ write like this is not allowed: * p = & a, * p indicates the bucket pointed to by the Access pointer p. ④ the definition variable * is just a symbol and has no special meaning.

2. pointer to pointer 1. Example

Char a = 'a ';

Char * p = & a; // pointer to a char-type Bucket

Char ** pp = & p; // pointer to pointer

Char *** ppp = & pp; // Level 3 pointer (not commonly used)

 

2. pointer Application

1> call a function to obtain multiple return values

1 # include <stdio. h> 2 3 int sumAndMinus (int num1, int num2, int * num3) 4 {5 * num3 = num1-num2; 6 return num1 + num2; 7} 8 9 10 int main () 11 {12 int a = 12; 13 int B = 8; 14 int minus; 15 int sum = sumAndMinus (a, B, & minus); 16 return 0; 17}Multiple return values 3. Memory occupied by pointers

* Pointer memory usage is related to the specific compiler. In Xcode, pointers of any type occupy 8 bytes.

3. pointer and array 1. array Traversal

// Use subscript for Traversal

Int nums [3] = {1, 2, 3 ,}

For (int I = 0; I <3; I ++)

{

Printf ("% d \ n", nums [I]);

}

2. traverse the Array Using pointers

Int nums [3] = {1, 2, 3 ,};

Int * p = & nums;

// Pointer p points to the address of the first element of the array;

// (P + 1) points to nums [1];

For (int I = 0; I <3; I ++)

{

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

Printf ("% d \ n", p [I]);

}

4. pointer and string, pointer array 1. character array and string comparison

Char c1 [] = "name ";

// The above line of code indicates a character array, which represents a string variable

Char * c2 = "name ";

// The above line of code. The pointer variable c2 points to the first letter of the string. It indicates a String constant.

// The differences between the two lines of code are also related to the storage of data in the memory.

Char * c3 = "name ";

// Note: c2 and c3 are the same address.

2. Two Methods for defining strings

1> Use Arrays

Char c [] = "name ";

// Features: the characters in the string can be modified.

// Usage: the string content needs to be modified frequently.

2> Use Pointer

Char * c = "name ";

// Feature: the character string is actually a constant string, and the characters in it cannot be modified.

// Usage: the content of the string does not need to be modified, and this string is often used.

3. pointer Array

1> pointer array Definition

Char * name [3] = {"jack", "rose", "tom "};

2> string Input

// Create a new character array to save the string entered by the user

Char name [20];

// The array name indicates the address of the first element of the array.

Scanf ("% s", name );

5. pointer to the function and function that returns the pointer 1. function that returns the pointer

Char * test ()

{

Return "name ";

}

Int main ()

{

Char * p = test ();

Return 0;

}

2. pointer to function

Void test ()

{

Printf ("test function called ");

}

Int main ()

{

// (* P) is a fixed writing method, which indicates that the pointer Variable p will definitely point to the function in the future.

// Void on the left: no return value is returned for the function pointed to by the pointer Variable P.

// () On the Right: The pointer Variable p points to the function with no form parameters

Void (* p )();

// The function name is the function address.

P = test;

// Function call Methods

(* P) (); // Method 1: directly call

Test (); // Method 2: Use Pointer to call

P (); // method 3: Use Pointer to call

Return 0;

}