1.calloc与realloc的使用

void *malloc(size_t size)

size -- 内存块的大小，以字节为单位

该函数返回一个指针 ，指向已分配大小的内存。如果请求失败，则返回 NULL。

void *realloc(void *ptr, size_t size)

size -- 内存块的新的大小，以字节为单位。如果大小为 0，且 ptr 指向一个已存在的内存块，则 ptr 所指向的内存块会被释放，并返回一个空指针。

该函数返回一个指针 ，指向重新分配大小的内存。如果请求失败，则返回 NULL。

#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<stdlib.h>#include<string.h>#include<time.h>static void test01(){    //int* p = malloc(sizeof(int) * 10);//开辟出堆区的内存是未知数据    int* p = calloc(10, sizeof(int));//calloc会将堆区分配的内容初始化为0    for (int i = 0; i < 10; i++)    {        printf("%d\n", p[i]);    }    if (p!= NULL)    {        free(p);        p = NULL;    }}//realloc重新在堆区分配内存static void test02(){    int* p = malloc(sizeof(int) * 10);    printf("%d\n", p);    for (int i = 0; i < 10; i++)    {        p[i] = i;    }    p = realloc(p, sizeof(int) * 20);    for (int i = 0; i < 20; i++)    {        printf("%d\n",p[i]);    }    printf("%d\n", p);    if (p != NULL)    {        free(p);        p = NULL;    }}int main01(){    //test01();    test02();    return 0;}

2.sscanf的使用

#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<stdlib.h>#include<string.h>#include<time.h>//1、%*s或%*d  跳过数据static void test01(){    char* str = "123abcd";    char buf[1024] = { 0 };    sscanf(str, "%*d%s", buf);//从str中读取字符串 忽略%d打印出%s  输出到buf中    printf("%s\n", buf);}static void test02(){    char* str = "abcd12345";//在中间加空格或者\t都可以实现取出数字的效果    char buf[1024] = { 0 };    //sscanf(str, "%*s%s", buf);    sscanf(str, "%*[a-z]%s", buf);//忽略a~z    printf("%s\n", buf);}//2、%[width]s  读取指定宽度的数据static void test03(){    char* str = "1234abcd";    char buf[1024] = { 0 };    sscanf(str, "%6s", buf);    printf("%s\n", buf);}//3、%[a-z]匹配a~z中任意字符static void test04(){    char* str = "12345abcde";    char buf[1024] = { 0 };    sscanf(str, "%*d%[a-c]", buf);//忽略数组匹配a~c    printf("%s\n", buf);}//4、%[aBc]匹配a、B、c中的一员，贪婪性static void test05(){    char* str = "aabcde12345";    char buf[1024] = { 0 };    sscanf(str, "%[aBc]", buf);//匹配过程中只要有一个失败了，后续不再进行匹配    printf("%s\n", buf);//aa}//5、%[^a]匹配非a的任意字符，贪婪性static void test06(){    char* str = "abcde12345";    char buf[1024] = { 0 };    sscanf(str, "%[^c]", buf);    printf("%s\n", buf);//ab}//6、%[^a-z]读取除a~z以外的所有字符static void test07(){    char* str = "abcde12345";    char buf[1024] = { 0 };    sscanf(str, "%[^0-9]", buf);    printf("%s\n", buf);//abcde}//7、案例static void test08(){    char* ip = "127.0.0.1";    int num1 = 0;    int num2 = 0;    int num3 = 0;    int num4 = 0;    sscanf(ip, "%d.%d.%d.%d", &num1, &num2, &num3, &num4);    printf("%d\n", num1);    printf("%d\n", num2);    printf("%d\n", num3);    printf("%d\n", num4);}static void test09(){    char* str = "abcde#longGG@12345";    char buf[1024] = { 0 };    sscanf(str, "%*[^#]#%[^@]", buf);    printf("%s\n", buf);}static void test10(){    char* str = "helloworld@itcase.cn";    char buf1[1024] = { 0 };    char buf2[1024] = { 0 };    sscanf(str, "%[a-z]%*[@]%s", buf1, buf2);    printf("%s\n", buf1);//helloworld    printf("%s\n", buf2);//itcase.cn}int main02(){    //test01();    //test02();    //test03();    //test04();    //test05();    //test06();    //test07();    //test08();    //test09();    test10();    return 0;}

3.查找子串

#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<stdlib.h>#include<string.h>#include<time.h>int mystrcpy(char* str, char* substr){    int num = 0;    while (*str != '\0')    {        if (*str != *substr)        {            str++;            continue;        }        //创建临时指针        char* tmpstr = str;        char* tmpsubstr = substr;        while (*tmpsubstr != '/0')        {            if (*tmpstr != *tmpsubstr)            {                //匹配失败                str++;                num++;                break;            }            tmpstr++;            tmpsubstr++;        }        if (*tmpsubstr == '\0')        {            //匹配成功            return num;        }    }    return -1;}static void test01(){    char* str = "abcdefghdnf";    int ret = mystrcpy(str, "dnf");    if (ret == -1)    {        printf("未找到子串\n");    }    else    {        printf("找到子串位置是:%d\n", ret);    }}int main03(){    test01();    return 0;}

4.const使用场景

#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<stdlib.h>#include<string.h>#include<time.h>struct person{    char name[64];    int age;    int id;    double score;};//const使用场景：修饰函数中的形参，防止误操作static void printperson(const struct person *p){    //p->age = 100;加入const之后编译器会检测误操作    printf("姓名：%s,年龄：%d，学号：%d,成绩：%d\n", p->name, p->age, p->id, p->score);}static void test01(){    struct person p1 = {"张飒",22,01,78};	printperson(&p1);    printf("p1年龄：%d\n", p1.age);}int main05(){    test01();    return 0;}

5.二级指针作为函数参数的输入特性

#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<stdlib.h>#include<string.h>#include<time.h>//二级指针做函数参数的输入特性//主调函数分配内存，被调函数使用static printarr(int**parr,int len){    for (int i = 0; i < len; i++)    {        printf("%d\n", *parr[i]);    }}static void test01(){    //在堆区分配内存    int** p = malloc(sizeof(int*) * 5);    //在栈区创建数据    int a1 = 10;    int a2 = 20;    int a3 = 30;    int a4 = 40;    int a5 = 50;    p[0] = &a1;    p[1] = &a2;    p[2] = &a3;    p[3] = &a4;    p[4] = &a5;    printarr(p, 5);    if (p != NULL)    {        free(p);        p = NULL;    }}static void test02(){    //在栈区创建    int* parr[5];    for (int i = 0; i < 5; i++)    {        parr[i] = malloc(4);        *(parr[i]) = 100 + i;    }    int len = sizeof(parr) / sizeof(int*);    printarr(parr, len);    for (int i = 0; i < 5; i++)    {        if (parr[i] != NULL)        {            free(parr[i]);            parr[i] = NULL;        }    }}int main06(){    //test01();    test02();    return 0;}

6.二级指针作为函数参数的输出特性

#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<stdlib.h>#include<string.h>#include<time.h>static allocatespace(int** p){	int* arr = malloc(sizeof(int) * 10);    for(int i = 0; i < 10; i++)    {        arr[i] = i + 10;    }    *p = arr;}static void printarray(int**parr,int len){    for (int i = 0; i < 10; i++)    {        printf("%d\n", (*parr)[i]);    }}static void freespace(int**p){    if (*p != NULL)    {        free(*p);        *p = NULL;    }}static void test01(){    int* p = NULL;    allocatespace(&p);    printarray(&p, 10);    freespace(&p);}int main07(){    test01();    return 0;}

7.二级指针文件读写

#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<string.h>#include<stdlib.h>//获取文件的行数int getFileLines(FILE* file){	if (file == NULL)	{		return -1;	}	char buf[1024]; //读取的数据存入到buf	int num = 0;	while (fgets(buf, 1024, file) != NULL)	{		num++;		//printf("%s", buf);	}	//将文件光标 置为文件首	fseek(file, 0, SEEK_SET);	return num;}//参数1 文件指针  参数2  有效函数  参数3  堆区数组void readFileData(FILE* file, int len, char** pArray){	if (file == NULL)	{		return;	}	if (len <= 0)	{		return;	}	if (pArray == NULL)	{		return;	}	char buf[1024]; //读取的数据存入到buf	int index = 0;	while (fgets(buf, 1024, file) != NULL)	{		//buf中就是存放的每行的数据				int currentLen = strlen(buf) + 1;		char* currentP = malloc(sizeof(char) * currentLen);		//将数据拷贝到堆区内存中		strcpy(currentP, buf);		pArray[index++] = currentP;		//清空缓冲区		memset(buf, 0, 1024);	}}void showFileData(char** pArray, int len){	for (int i = 0; i < len; i++)	{		printf("第 %d 行的数据为 %s", i + 1, pArray[i]);	}}void freeSpace(char** pArray, int len){	for (int i = 0; i < len; i++)	{		if (pArray[i] != NULL)		{			free(pArray[i]);			pArray[i] = NULL;		}	}	free(pArray);	pArray = NULL;}void test01(){	FILE* file = fopen("f:/a.txt", "r");	if (file == NULL)	{		printf("文件打开失败\n");		return;	}	int len = getFileLines(file);	printf("文件的有效行数为：%d\n", len);	char** pArray = malloc(sizeof(char*) * len);	//将文件中的数据 读取后 放入到pArray中	readFileData(file, len, pArray);	//打印数据	showFileData(pArray, len);	//释放数据	freeSpace(pArray, len);	pArray = NULL;	//关闭文件	fclose(file);	file = NULL;}int main08() {	test01()；	system("pause");	return EXIT_SUCCESS;}

8.按位取反、或、与、左移和右移

#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<stdlib.h>#include<string.h>#include<time.h>//1、按位取反~static void test01(){    int num = 2;    printf("~num=%d\n", ~num);//-3    //010按位取反    101原码    //101补码   110+1=111   最高位是符号位}//2、按位与static void test02(){    int num = 123;    if((num & 1) == 0)    {        printf("num为偶数\n");    }    else    {        printf("num为奇数\n");//奇    }}//3、按位或static void test03(){    int num1 = 5;    int num2 = 3;    printf("num1|num2=%d\n", num1 | num2);//7}//4、三种方式交换两个数字static void test04(){    int num1 = 10;    int num2 = 20;    //方式1    //int temp = num1;    //num1 = num2;    //num2 = temp;    //按位异或方式2    num1 = num1 ^ num2;    num2 = num1 ^ num2;     num1 = num1 ^ num2;    //不用临时变量实现两个数字交换    //num1 = num1 + num2;    //num2 = num1 - num2;    //num1 = num1 - num2;    printf("交换后\n");    printf("num1=%d\n", num1);    printf("num2=%d\n", num2);}//左移运算符static void test05(){    int num = 10;    printf("%d\n", num <<= 2);//  <<n即乘以2的n次方}//右移运算符static void test06(){    int num = 10;    printf("%d\n", num >>= 1);//  >>n即除以2的n次方}int main(){	//test01();	//test02();	//test03();	//test04();    //test05();    test06();    return 0;}