8.11 Dynamic memory allocation and pointer variables pointing to it.mp4慕课视频播放-C Programming-MOOC慕课视频教程-柠檬大学

大家好

我是云南大学信息学院丁海燕老师

欢迎走进C语言程序设计课堂

今天我们讲解动态内存分配与指向它的指针变量

什么是动态内存分配呢？

非静态的局部变量

是分配在内存中的动态存储区的

这个存储区是一个称为栈的区域

C语言还允许建立内存动态分配区域

以存放一些临时用的数据

这些数据需要时随时开辟

不需要时随时释放

这些数据是临时存放在一个特别的自由存储区，称为堆区

怎样建立内存的动态分配呢？

对内存的动态分配是通过系统提供的库函数来实现的

主要有malloc，calloc，free，realloc这4个函数

1. malloc函数

其函数原型为

void *malloc(unsigned int size);

其作用是在内存的动态存储区中分配一个长度为size的连续空间

– 函数的值是所分配区域的第一个字节的地址

或者说，此函数是一个指针型函数，

返回的指针指向该分配域的开头位置

例如malloc(100);

开辟100字节的临时分配域

函数值为其第1个字节的地址

注意指针的基类型为void

即不指向任何类型的数据

只提供一个地址

如果此函数未能成功地执行（例如内存空间不足）

则返回空指针(NULL)

2．calloc函数

其函数原型为

void *calloc(unsigned n,unsigned size);

其作用是在内存的动态存储区中

分配n个长度为size的连续空间

这个空间一般比较大，足以保存一个数组

用calloc函数可以为一维数组开辟动态存储空间

n为数组元素个数

每个元素长度为size

这就是动态数组

函数返回指向所分配域的起始位置的指针

如果分配不成功，返回NULL

如： p=calloc(50,4)

开辟50×4个字节的临时分配域

把起始地址赋给指针变量p

3．free函数

其函数原型为void free(void *p);

其作用是释放指针变量ｐ所指向的动态空间

使这部分空间能重新被其他变量使用

p应是最近一次调用calloc或malloc函数时得到的函数返回值

free(p);

释放指针变量ｐ所指向的已分配的动态空间

free函数无返回值

4. realloc函数

其函数原型为

void *realloc(void *p,unsigned int size)

如果已经通过malloc函数或calloc函数获得了动态空间

想改变其大小

可以用recalloc函数重新分配

用realloc函数将p所指向的动态空间的大小改变为size

p的值不变

如果重分配不成功，返回NULL

如：realloc(p,50)

将p所指向的已分配的动态空间改为50字节

以上4个函数的声明在stdlib.h头文件中

在用到这些函数时应当用“#include ”指令

指令把stdlib.h头文件包含到程序文件中

下面介绍void指针类型

下面来看例8.30

建立动态数组，输入5个学生的成绩

另外用一个函数检查其中有无低于60分的

输出不合格的成绩

解题思路：

用malloc函数开辟一个动态自由区域

用来存5个学生的成绩

会得到这个动态域第一个字节的地址

它的基类型是void型

用一个基类型为int的指针变量p来指向动态数组的各元素

并输出它们的值

但必须先把malloc函数返回的void指针转换为整型指针

然后赋给p1

程序如下：

{ void check(int *)

声明函数

int *p1,i

p1是int型指针

p1=(int *)malloc(5*sizeof(int))

开辟动态内存区

将地址转换成int *型

然后放在p1中

for(i=0;i<5;i++)

scanf("%d",p1+i)

输入5个学生的成绩

check(p1)

调用check函数

check函数定义如下：

void check(int *p)

定义check函数形参是int *指针

for(i=0;i<5;i++)

if (p[i]<60)

输出p[i]) 的值

即输出不合格的成绩

例如：输入67 98 59 78 57

输出They are fail:59 57

好了，同学们

动态内存分配与指向它的指针变量

我们就学习到这儿

下节课再见

C Programming课程列表：

Chapter 1 Introduction

-1.1 The development and characteristics of C language

--1.The development and characteristics of C language .mp4

--1.1 Self test questions

-1.2 A simple C Language program

--1.2 A simple C Language program.mp4

--Discussion unit

--【Source program】 Example 1.1 output a line of text Hello, world! "

--【Source program】 Example 1.2 program composed of multiple functions, find the larger of two integers

--1.2 Self test questions

-1.3 Program, Programming Language and C Program Running Steps

--1.3 Program, Programming Language and C Program Running Steps.mp4

--Discussion unit

--Running steps of C source program in CodeBlocks

--1.3 Self test questions

-Course references

-chapter 1 Self-Test

Chapter 2 Algorithm

-2.1 The Concept and Description of Algorithms

--2.1 The Concept and Description of Algorithms.mp4

--Discussion unit

--2.1 Self test questions

-2.2 Examples of Simple Algorithms, Computational Thinking and Structured Programming

--2.2 Examples of Simple Algorithms, Computational Thinking and Structured Programming.mp4

--Discussion unit

--2.2 Self test questions

-Chapter 2 Self test questions

Chapter 3 Programming in C

-3.1 Simple Structure and Identifier of C Language Program

--3.1 Simple Structure and Identifier of C Language Program.mp4

--【Source program】 Example 3.1 input two integers and output the sum of two numbers.

--【Source program】 Example 3.2 input two integers and output the average value.

--【Source program】 Example 3.3 output the value of the character variable.

--3.1 Self test questions

-3.2 Constants, Variables and Assignments

--3.2 Constants, Variables and Assignments.mp4

--Discussion unit

--3.2 Self test questions

-3.3 Arithmetic, assignment, increment and decrement operators

--3.3 Arithmetic, assignment, increment and decrement operators.mp4

--3.3 Self test questions

-3.4 Conditions, commas, addresses, byte operators, and mixed operations among various numerical data

--3.4 Conditions, commas, addresses, byte operators, and mixed operations among various numerical data

--【Source program】 example of sizeof

--3.4 Self test questions

-3.5 Input and Output Examples and Character Input and Output

--3.5 Input and Output Examples and Character Input and Output.mp4

--【Source program】 Example. Find the root of quadratic equation of one variable.

--【Source program】 Example 1. Successively output three characters of BOY.

--【Source program】Example 2. Input 3 characters of BOY from the keyboard and output them to the screen

--3.5 Self test questions

-3.6 Formatted output printf function

--3.6 Formatted output printf function.mp4

--【Source program】 Example 3.4 output of integer data.

--【Source program】 Example 3.5 real data output.

--【Source program】 Example 3.6 character data output.

--【Source program】 Example 3.7 uses %s to output a string.

--3.6 Self test questions

-3.7 Formatted input scanf function

--3.7 Formatted input scanf function.mp4

--Discussion unit

--【Source program】 Example 3.8 Input and output integer data

--【Source program】Example 3.9 Input and output single precision and double precision real data.

--【Source program】Example 3.10 input and output character data.

--【Source program】Example 3.11 input and output string.

--3.7 Self test questions

-3.8 Basic Data Types of C Language

--3.8 Basic Data Types of C Language.mp4

--3.8 Self test questions

-Chapter 3 Self test questions

-Operator and expression self test questions

Chapter 4 Selection Structure

-4.1 Relational operators, logical operators, and if statements

--4.1 Relational operators, logical operators, and if statements.mp4

--Discussion unit

--【source example】Example 4.1 Find the root of the quadratic equation of one variable.

--【Source program】Example 4.2 Input two real numbers and output them from small to large.

--4.1 Self test questions

-4.2 Switch Statement

--4.2 Switch Statement .mp4

--Discussion unit

--【Source program】Example 4.3 uses switch statement to implement simple menu program

--【Source program】Example 4.4 converts centesimal score into the corresponding grade system score.

--4.2 Self test questions

-4.3 Examples of Selection Structural Programs

--4.3 Examples of Selection Structural Programs.mp4

--【Source program】 Example 4.5 determines whether a year is a leap year.

--【Source program】 Example 4.6 find the solution of quadratic equation of one variable.

--【Source program】Example 4.7 calculate the transportation cost for the user.

--4.3 Self test questions

-Chapter 4 Self test questions

Chapter 5 Loop Structure

-5.1 While and Do-While Statement

--5.1 While and Do…while statement.mp4

--Discussion unit

--【Source program】example 5.1 Use while statement to find 1 + 2 + 3 + +100

--【Source program】example 5.2 using do while statement to find 1 + 2 + 3 + +100

--5.1 Self test questions

-5.2 For Statement

--5.2 for statement.mp4

--【Source program】example 5.3 Use for loop to find 1 + 2 + 3 +100

--5.2 Self test questions

-5.3 Change the State of Loop Execution and Nested Loop

--5.3 Change the state of loop execution and nested loop .mp4

--【Source program】example 5.4 collecting charity donations

--【Source program】example 5.5 output a number between 100 and 200 that cannot be divided by 3.

--【Source program】multiplication table

--【Source program】example 5.6 Output the following 4*5 matrix.

--5.3 Self test questions

-5.4 Loop Structure Program example 1

--5.4 Loop structure program example 1.mp4

--【Source program】example 1

--【Source program】example 2

--【Source program】example 3

--【Source program】 Example 4

--5.4 Self test questions

-5.5 Loop Structure Program example 2

--5.5 Loop structure program example 2.mp4

--【Source program】example 5. Output the following figure.

--【Source program】example6. The problem of 100 chickens and 100 coins

--【Source program】example 7. Find the approximate value of PI

--5.5 Self test questions

-Chapter 5 Self test questions

Chapter 6 Batch Data Processing with Array

-6.1 Definition, Reference and Initialization of One-Dimensional Arrays

--6.1 Definition, Reference of One-Dimensional Arrays.mp4

--Discussion unit

--6.1 Self test questions

-6.2 One-Dimensional Array Programming

--6.2 One-Dimensional Array Programming.mp4

--【Source program】example 1. Fibonacci sequence

--【Source program】example 2. Find the maximum value and the minimum value.

--【Source program】example 3 exchanging array elements in reverse order.

--【Source program】example 4. Bubble sorting.

--6.2 Self test questions

-6.3 Definition, Reference and Initialization of Two-Dimensional Arrays

--6.3 Definition, Reference of Two-Dimensional Arrays.mp4

--6.3 Self test questions

-6.4 Two-Dimensional Array Programming

--6.4 Two-Dimensional Array Programming.mp4

--【Source program】example 1. Get the average score of each subject.

--【Source program】Example 2. The elements of row and column of a 2D array are interchanged

--6.4 Self test questions

-6.5 Definition, initialization and input and output of character arrays

--6.5 Definition, initialization and input and output of character arrays .mp4

--Discussion unit

--【Source program】Example 6.6 Output a known string.

--【Source program】Example 6.7 Output a diamond.

--【Source program】Example 6.10 Sorting of strings.

--6.5 Self test questions

-6.6 String Processing Function

--6.6 String Processing Function.mp4

--6.6 Self test questions

-6.7 Character Array Programming

--6.7 Character Array Programming.mp4

--6.7 Self test questions

-Chapter 6 Self test questions

Chapter 7 Modular Programming with Functions

-7.1 Function Concept and How to Define and Call Functions

--7.1 Function Concept and How to Define and Call Functions.mp4

--【Source program】Example 7.1

--7.1 Self test questions

-7.2 Data Transfer in Function Call, Call Procedure and Function Return Value

--7.2 Data Transfer in Function Call, Call Procedure and Function Return Value.mp4

--Discussion unit

--【Source program】Example 7.2

--7.2 Self test questions

-7.3 Declarations of called functions and nested calls to functions

--7.3 Declarations of called functions and nested calls to functions .mp4

--【Source program】Example 7.4 use a function to find the sum of t

--7.3 Self test questions

-7.4 Recursive call to function

--7.4 Recursive call to function.mp4

--【Source program】Example 7.6. How old is the fifth student?

--【Source program】Example 7.7 Use recursion method to find n!

--7.4 Self test questions

-7.5 Array as function parameter (1)

--7.5 Array as function parameter (1).mp4

--Discussion unit

--【Source program】Example 7.10

--7.5 Self test questions

-7.6 Array as function parameter (2)

--7.6 Array as function parameter (2).mp4

--【Source program】Selection sorting.

--【Source program】Example 7.13 find the maximum of a 3×4 matrix.

--7.6 Self test questions

-7.7 Local and global variables, internal and external functions

--7.7 Local and global variables, internal and external functions.mp4

--【Source program】Example 7.14

--7.7 Self test questions

-7.8 The Survival Period of Variables and the Storage Mode of Local Variables

--7.8 The Survival Period of Variables and the Storage Mode of Local Variables.mp4

--【Source program】Example 7.17

--7.8 Self test questions

-7.9 Storage Categories of Global Variables

--7.9 Storage Categories of Global Variables.mp4

--7.9 Self test questions

-Chapter 7 Self test questions

Chapter 8 Pointer

-8.1 Pointer Concept, Definition and Reference of Pointer Variables

--8.1 Pointer Concept, Definition and Reference of Pointer Variables.mp4

--【Source program】Example 8.1

--8.1 Self test questions

--Discussion unit

-8.2 Pointer variables as function parameters

--8.2 Pointer variables as function parameters.mp4

--Discussion unit

--【Source program】Example 8.3. Exchange two data with function call.

--8.2 Self test questions

-8.3 Pointer of array element, operation of pointer and reference of array element by pointer

--8.3 Pointer of array element, operation of pointer and reference of array element by pointer.mp4

--【Source program】Point to array elements with pointer variables.

--8.3 Self test questions

-8.4 Using Array Name as Function Parameter

--8.4 Using Array Name as Function Parameter.mp4

--【Source program】Store array elements in reverse order.

--8.4 Self test questions

-8.5 Reference to multidimensional arrays by pointers

--8.5 Reference to multidimensional arrays by pointers.mp4

--【Source program】Pointer variable pointing to one-dimensional array.

--8.5 Self test questions

-8.6 Referencing strings through pointers

--8.6 Referencing strings through pointers.mp4

--【Source program】Reference string by pointer.

--8.6 Self test questions

-8.7 Character pointer as function parameter

--8.7 Character pointer as function parameter.mp4

--【Source program】Character pointer as function parameter.

--8.7 Self test questions

-8.8 Pointer pointing to function

--8.8 Pointer pointing to function.mp4

--【Source program】Pointer variable pointing to the function.

--8.8 Self test questions

-8.9 Functions that return pointer values

--8.9 Functions that return pointer values.mp4

--【Source program】Intercept substring.

--8.9 Self test questions

-8.10 Pointer arrays and multiple pointers

--8.10 Pointer arrays and multiple pointers.mp4

--【Source program】Sorting of strings.

--8.10 Self test questions

-8.11 Dynamic memory allocation and pointer variables pointing to it

--8.11 Dynamic memory allocation and pointer variables pointing to it.mp4

--Discussion unit

--【Source program】Dynamic memory allocation.

--8.11 Self test questions

-Chapter 8 Self test questions

Chapter 9 Structure

-9.1 Define and use structural variables

--9.1 Define and use structural variables.mp4

--【Source program】Structure variable

--9.1 Self test questions

-9.2 Using structure arrays

--9.2 Using structure arrays.mp4

--Discussion unit

--【Source program】Structure array

--9.2 Self test questions

-9.3 Structure pointer

--9.3 Structure pointer.mp4

--【Source program】Structure pointer

--9.3 Self test questions

-Chapter 9 Self test questions

CodeBlocks Baidu online disk download

-CodeBlocks Baidu online disk download address

Final Exam

-Final Exam

--final exam

8.11 Dynamic memory allocation and pointer variables pointing to it.mp4在线视频

8.11 Dynamic memory allocation and pointer variables pointing to it.mp4课程教案、知识点、字幕

C Programming课程列表：

Chapter 1 Introduction

Chapter 2 Algorithm

Chapter 3 Programming in C

Chapter 4 Selection Structure

Chapter 5 Loop Structure

Chapter 6 Batch Data Processing with Array

Chapter 7 Modular Programming with Functions

Chapter 8 Pointer

Chapter 9 Structure

CodeBlocks Baidu online disk download

Final Exam

8.11 Dynamic memory allocation and pointer variables pointing to it.mp4笔记与讨论

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