Pointers Basic Concepts

First, the pointer Prelude 1. The importance of pointers

Pointers are a very important type of data in C, and if you say that you have a good study in c except for pointers, you simply say you have not learned C language.

2. Small needs

(1) When the Void change (int n) function call is complete, the value of the argument is changed

(2) Analysis: Change the value of the argument, find storage space, address

Second, the pointer variable definition 1. The format of the definition

(1) class name identifier * pointer variable name;

int *p;

2. Define the Post assignment first

(1) Simple value

int a = 10;

int *p;

p = &a;

printf ("%d", *p);

(2) Simple change of value

*p = 9;

3. Assigning values at the same time as defined

int a = 10;

int *p = &a;

4. Implement modify argument 5. Watch out.

(1) int *p; p = 1000;

(2) int *p; *p = 100;

(3) int *p; *p = &a;

(4) The address value stored in the%p output pointer

(5) Other pointer type description, such as float *p; Char *p;

(6) The type cannot be used indiscriminately, such as int a = 10; float *p = &a;

6. Clear the pointer

(1) p = 0;

(2) p = NULL;

Third, pointer instances

(1) void swap (char *a, char *b) (note temp=a; A = b; b = temp;)

(2) int Sumandminus (int a, int b, int *minus)

Iv. the research of pointers

(1) The storage space occupied by the pointer variable

(2) Why are pointer variables divided into types?

int i = 2;

char c = 1;

int *p = &c;

printf ("%d", *p);

V. Pointers and Arrays 1. Pointer to a one-dimensional array element 2. Traversing one-dimensional array elements with pointers

(1) Iterate through the char array (' I ', ' t '), and then iterate through the array of int types

(2) * (P+i) and * (p++) difference

(3) A+i and a++

(4) p[0], p[1]

3. Exercises

(1) A function is designed: int arraysum (int a[], int n), and the number of the first n of a one-dimensional array is obtained. Now replace int a[with int *p]

Six, pointers and strings 1. String review

Char s[] = "MJ";

2. Other ways to define strings

Char *s = "MJ";

Or

Char *s;

s = "MJ";

3. The difference between the two ways of definition

(1) Memory analysis

(2) Drawing analysis

(3) The difference between a constant and a variable string

(4) Constant memory address view

4. Exercises

(1) write an int string_len (char *s) to return the character length of the string s

Functions for returning pointers

(1) Pointers are also a type of data in C, so the return value of a function can certainly be a pointer-type

(2) The general form of a function that returns a pointer is: type name * function name ( parameter list)

Eight, pointer to function 1. Why can pointers point to a function?

function as a program, in memory also occupy a portion of storage space, it also has a starting address, that is, the entry address of the function. function has its own address, that's good, our pointer variable is used to store the address. Therefore, a pointer can be used to point to a function. Where the function name represents the address of the function.

2. Definition of pointers to functions

General form of definition: The return value type of the function (* pointer variable name) ( parameter 1, parameter 2, ...);

3. Use note

(1) Since this type of pointer variable stores the entry address of a function, it is meaningless to add or subtract them (such as p++).

(2) Pointer variables pointing to functions have a primary purpose of two:

• Calling functions
• Passing functions as arguments between functions

Pointers Basic Concepts