C语言结构体（struct）学习

不念不忘少年蓝@ 2022-12-09 02:44 324阅读 0赞

# 结构初始化 #

#include<stdio.h>
    #include<string.h>
    char * s_gets(char * st, int n);
    #define MAXTITL 41
    #define MAXAUTL 31
    //结构体 
    struct book{
        
    	char title[MAXTITL];
    	char author[MAXAUTL];
    	float value;
    };
    
    int main(void)
    {
        
    	struct book library;//把library声明为一个book类型的变量
    	//初始化结构体 
    	struct book b1 = {
        
    		"The Greats Gyciby",
    		"luo",
    		22.8
    	};
    	//结构的初始化器
    	struct book b2 = {
        
    		.value = 19.23,
    		.author = "James Bonds",
    		.title = "007",
    		"test",//对成员的最后一次赋值才是他真实的值，这里赋给author的值为“test”，因为在结构体声明中，title后面是author 
    		666//同理，value会变成666 
    	}; 
    //	printf("Please enter the book title.\n");
    //	s_gets(library.title, MAXTITL);
    //	printf("Now enter the author.\n");
    //	s_gets(library.author, MAXAUTL);
    //	printf("Now enter the value.\n");
    //	scanf("%f",&library.value);
    //	printf("%s by %s：$%.2f\n", library.title, library.author, library.value);
    	printf("%s by %s：$%.2f\n", b1.title, b1.author, b1.value);
    	printf("%s by %s：$%.2f\n", b2.title, b2.author, b2.value);
    	puts("Done!");
    	
    	return 0;	
    } 
    
    char * s_gets(char * st, int n){
        
    	char * ret_val;
    	int i = 0;
    	
    	ret_val = fgets(st, n, stdin);//如果一切进行顺利，返回的是第一个字符的地址 ,遇到文件结尾或者错误时返回NULL 
    	if(ret_val){
        //如果输入成功 
    		while (st[i] != '\n' && st[i] != '\0')//跳转到字符串末尾 
    			i++;
    		if(st[i] == '\n')//替换掉换行符 
    			st[i] = '\0';
    		else//如果输入字符串超出字数，之后的字符就省略 
    			while (getchar() != '\n')
    				continue;
    	} 
    	return ret_val;//输入正常则返回字符串首字符地址 
    }

# 结构数组 #

//包含多本书的结构数组
    #include<stdio.h>
    #include<string.h>
    char * s_gets(char * st, int n);
    #define MAXTITL 41
    #define MAXAUTL 31 
    #define MAXBKS 100
    
    //结构体 
    struct book{
        
    	char title[MAXTITL];
    	char author[MAXAUTL];
    	float value;
    };
    
    int main(void)
    {
        
    	struct book library[MAXBKS];//book类型的结构数组
    	int count = 0;
    	int index;
    	
    	printf("Please enter the book title.\n");
    	while(count < MAXBKS && s_gets(library[count].title, MAXTITL) != NULL && library[count].title[0] != '\0')
    	{
        
    			printf("Now enter the author.\n");
    			s_gets(library[count].author, MAXAUTL);
    			printf("Now enter the value.\n");
    			scanf("%f",&library[count++].value);
    			
    			while (getchar() != '\n')
    				continue;
    			if(count < MAXBKS)
    				printf("Enter the next title.\n");
    	} 
    	if(count > 0)
    	{
        
    		printf("Here is the list of your books:\n");
    		for (index = 0; index < count; index++)
    		{
        
    			printf("%s by %s：$%.2f\n", library[index].title, library[index].author, library[index].value);	
    		}
    
    	}		
    	else
    			printf("No books?");
    	return 0;
    }
    
    char * s_gets(char * st, int n)
    {
        
    	char * ret_val;
    	char * find;
    	
    	ret_val = fgets(st, n, stdin);
    	if(ret_val)
    	{
        
    		find = strchr(st, '\n');//查找换行符
    		if (find)//如果地址不是NULL 
    			*find = '\0'; //在此书放置一个空字符 
    		else
    			while (getchar() != '\n')
    				continue;  //处理输入行中其他字符
    		
    		 
    	}
    	
    	return ret_val; 
    	
    }

# 嵌套结构 #

在一个结构中包含另一个结构

# 指向结构的指针 #

//指向结构的指针
    #include<stdio.h>
    #define LEN 20
    
    struct names {
        
    	char first[LEN];
    	char last[LEN];
    }; 
    struct guy {
        
    	struct names handle;
    	char favfood[LEN];
    	char job[LEN];
    	float income;
    };
    
    int main(void)
    {
        
    	struct guy fellow[2] = {
        
    		{
        
    			{
        
    				"Kobe","James"
    			},
    			"bananas",
    			"basketball player",
    			999999.0
    		},
    		{
        
    			{
        
    				"Owing","Walker"
    			},
    			"Apples",
    			"basketball player",
    			666666.0
    		}
    	};
    	//声明 
    	struct guy * him;//指向结构的指针
    	
    	printf("address #1: %p #2: %p\n", &fellow[0], &fellow[1]);
    	
    	//初始化指针 
    	him = &fellow[0];//告诉编译器该指针指向何处
    	//和数组不同的是，结构名并不是结构的地址，所以要加&符号
    	
    	/*
    		用指针访问成员
    		第一种是最常用的方法：使用->运算符
    			如果him == &barney ,那么 him->income 就是 barney.income
    		第二种方法：由于him是一个指针，可以用 *him 来提取him指向的结构
    		barney.income == (*him).income == him->income 
    	*/ 
    	
    	printf("him->income is $%.2f: (*him).income is $%.2f\n",him->income , (*him).income) ;
    	him++;//指向下一个结构
    	printf("him->favfood is %s: him->handle.last is %s\n",him->favfood , him->handle.last) ;
    	 
    	return 0;
    }

# 结构和函数 #

//使用函数操作指向结构的指针
    #include<stdio.h>
    #include<string.h>
    
    #define NLEN 30
    struct namect {
        
    	char fname[NLEN];
    	char lname[NLEN];
    	int letters;
    }; 
    struct pnames {
        
    	char * f;
    	char * l;
    };
    struct names {
        
    	char f[100];
    	char l[100];
    };
    /*
    	函数不仅能把结构本身作为参数传递，还能把结构作为返回值返回 
    */
    struct namect changeinfo (struct namect);
    void getinfo(struct namect *);
    void makeinfo(struct namect *);
    void showinfo(const struct namect *);
    char * s_gets(char *st, int n);
    
    int main(void)
    {
        
    	struct namect person;
    	struct names n1 = {
        
    		"Kobjmuhe","Jackjm,m "
    	};
    	struct pnames n2 = {
        
    		"Kobe","Jack"
    	};	
    	/*
    		n1结构总共要分配200个字节存储姓名
    		而n2结构只存储了两个地址，所以在系统中占16个字节 
    	*/
    	printf("size of n1 = %u\n",sizeof(n1));
    	printf("size of n2 = %u\n",sizeof(n2));
    	getinfo(&person);
    	makeinfo(&person);
    	showinfo(&person);
    	person = changeinfo(person);
    	showstruct(person);
    	return 0;
    	
    }
    
    void getinfo(struct namect * pst)
    {
        
    	printf("Please enter your first name.\n");
    	s_gets(pst->fname, NLEN);
    	printf("Please enter your last name.\n");
    	s_gets(pst->lname, NLEN);
    }
    void makeinfo(struct namect * pst)
    {
        
    	pst->letters = strlen(pst->fname) + strlen(pst->lname);
    }
    void showinfo(const struct namect * pst)
    {
        
    	printf("%s %s,your name contains %d letters.\n",pst->fname,pst->lname,pst->letters);
    	printf("size = %u\n",sizeof(*pst));
    }
    
    struct namect changeinfo(struct namect info)
    {
        
    	 strcpy(info.fname,"best");
    	return info;
    }
    void showstruct(const struct namect pst)
    {
        
    	printf("%s %s,your name contains %d letters.\n",pst.fname,pst.lname,pst.letters);
    	printf("size = %u\n",sizeof pst);
    }
    
    char * s_gets(char * st, int n)
    {
        
    	char * ret_val;
    	char * find;
    	ret_val = fgets(st, n, stdin);
    	if(ret_val)
    	{
        
    		find = strchr(st, '\n');//查找换行符
    		if (find)//如果地址不是NULL 
    			*find = '\0'; //在此书放置一个空字符 
    		else
    			while (getchar() != '\n')
    				continue;  //处理输入行中其他字符			 
    	}
    	return ret_val; 	
    }

//使用函数操作指向结构的指针
    #include<stdio.h>
    #include<string.h>
    #include<stdlib.h>  //提供malloc()，free()等原型 
    
    #define NLEN 30
    #define SLEN 81
    struct pnamect {
        
    	char * fname;
    	char * lname;
    	int letters;
    }; 
    
    /*
    	函数不仅能把结构本身作为参数传递，还能把结构作为返回值返回 
    */
    void getinfo(struct pnamect *);
    void makeinfo(struct pnamect *);
    void cleanup(struct pnamect *);
    void showinfo(const struct pnamect *);
    char * s_gets(char *st, int n);
    
    int main(void)
    {
        
    	struct pnamect person;
    	getinfo(&person);
    	makeinfo(&person);
    	showinfo(&person);
    	//malloc和free应成对使用，程序结束时释放内存 
    	cleanup(&person);
    	return 0;
    }
    //使用指针和malloc() 
    void getinfo(struct pnamect * pst)
    {
        
    	char temp[SLEN];
    	printf("Please enter your first name.\n");
    	s_gets(temp, SLEN);
    	//分配内存以储存名称
    	pst->fname = (char *) malloc(strlen(temp) + 1);
    	//把名称拷贝到动态分配的内存中
    	strcpy(pst->fname,temp);
    	printf("Please enter your last name.\n");
    	s_gets(temp, SLEN);
    	pst->lname = (char *) malloc(strlen(temp) + 1);
    	strcpy(pst->lname, temp);
    } 
    void makeinfo(struct pnamect * pst)
    {
        
    	pst->letters = strlen(pst->fname) + strlen(pst->lname);
    }
    void showinfo(const struct pnamect * pst)
    {
        
    	printf("%s %s,your name contains %d letters.\n",pst->fname,pst->lname,pst->letters);
    	printf("size = %u\n",sizeof(*pst));
    }
    void cheanup(struct pnamect * pst){
        
    	free(pst->fname);
    	free(pst->lname); 
    }
    char * s_gets(char * st, int n)
    {
        
    	char * ret_val;
    	char * find;
    	ret_val = fgets(st, n, stdin);
    	if(ret_val)
    	{
        
    		find = strchr(st, '\n');//查找换行符
    		if (find)//如果地址不是NULL 
    			*find = '\0'; //在此书放置一个空字符 
    		else
    			while (getchar() != '\n')
    				continue;  //处理输入行中其他字符			 
    	}
    	return ret_val; 	
    }