C primer plus自用知识点整理（第十四章）结构和其他数据形式

书籍整理内容：
最近在看C primer plus（加深巩固自己的C语言技巧，为以后学习C++打个基础）。
里面知识针对自己以后要查的点整理出来。
使用工具：visual studio 2013
第二、三章内容：概述、变量、基本数据类型等：https://blog.csdn.net/answerMack/article/details/103766020
第四章内容：字符串和格式化输入输出：https://blog.csdn.net/answerMack/article/details/103805900
第五章内容：运算符、表达式和语句：https://blog.csdn.net/answerMack/article/details/103855794
第六章内容：循坏、赋值运算符等：https://blog.csdn.net/answerMack/article/details/103870182
第七章内容：if、if else、？：、switch、goto、continue、逻辑运算符优先级https://blog.csdn.net/answerMack/article/details/103891048
第八章内容：字符输入输出函数、输入验证（混合输入）https://blog.csdn.net/answerMack/article/details/103953376
第九章内容：函数和指针：https://blog.csdn.net/answerMack/article/details/103978471
第十章：数组和指针：https://blog.csdn.net/answerMack/article/details/104114028
第十一章：字符串和字符串函数：https://blog.csdn.net/answerMack/article/details/105222269
第十二章：存储类别、链接和内存管理：https://blog.csdn.net/answerMack/article/details/105338533
第十三章未更新

结构体

//* book.c -- one-book inventory */
#include 
#include 
char * s_gets(char * st, int n);
#define MAXTITL  41      /* maximum length of title + 1         */
#define MAXAUTL  31      /* maximum length of author's name + 1 */

struct book {            /* structure template: tag is book     */
	char title[MAXTITL];
	char author[MAXAUTL];
	float value;
};                       /* end of structure template           */

int main(void)
{
	struct book library; /* declare library as a book variable  */

	printf("Please enter the book title.\n");
	s_gets(library.title, MAXTITL); /* access to the title portion         */
	printf("Now enter the author.\n");
	s_gets(library.author, MAXAUTL);
	printf("Now enter the value.\n");
	scanf_s("%f", &library.value);
	printf("%s by %s: $%.2f\n", library.title,
		library.author, library.value);
	printf("%s: \"%s\" ($%.2f)\n", library.author,
		library.title, library.value);
	printf("Done.\n");

	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');   // look for newline
		if (find)                  // if the address is not NULL,
			*find = '\0';          // place a null character there
		else
			while (getchar() != '\n')
				continue;          // dispose of rest of line
	}
	return ret_val;
}

结构体的初始化：

访问结构成员

结构数组

/* manybook.c -- multiple book inventory */
#include 
#include 

char * s_gets(char * st, int n);
#define MAXTITL   40
#define MAXAUTL   40
#define MAXBKS   100              /* maximum number of books  */

struct book {                     /* set up book template     */
	char title[MAXTITL];
	char author[MAXAUTL];
	float value;
};

int main(void)
{
	struct book library[MAXBKS]; /* array of book structures */
	int count = 0;
	int index;

	printf("Please enter the book title.\n");
	printf("Press [enter] at the start of a line to stop.\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_s("%f", &library[count++].value);
		while (getchar() != '\n')
			continue;          /* clear input line         */
		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? Too bad.\n");

	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');   // look for newline
		if (find)                  // if the address is not NULL,
			*find = '\0';          // place a null character there
		else
			while (getchar() != '\n')
				continue;          // dispose of rest of line
	}
	return ret_val;
}

程序讨论

嵌套结构

#include 
#define LEN 20
const char * msgs[5] =
{
	"    Thank you for the wonderful evening, ",
	"You certainly prove that a ",
	"is a special kind of guy. We must get together",
	"over a delicious ",
	" and have a few laughs"
};

struct names {                     // first structure
	char first[LEN];
	char last[LEN];
};

struct guy {                       // second structure
	struct names handle;           // nested structure
	char favfood[LEN];
	char job[LEN];
	float income;
};

int main(void)
{
	struct guy fellow = {   // initialize a variable
		{ "Ewen", "Villard" },
		"grilled salmon",
		"personality coach",
		68112.00
	};

	printf("Dear %s, \n\n", fellow.handle.first);
	printf("%s%s.\n", msgs[0], fellow.handle.first);
	printf("%s%s\n", msgs[1], fellow.job);
	printf("%s\n", msgs[2]);
	printf("%s%s%s", msgs[3], fellow.favfood, msgs[4]);
	if (fellow.income > 150000.0)
		puts("!!");
	else if (fellow.income > 75000.0)
		puts("!");
	else
		puts(".");
	printf("\n%40s%s\n", " ", "See you soon,");
	printf("%40s%s\n", " ", "Shalala");

	return 0;
}

指向结构的指针

#include 
#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] = {
		{ { "Ewen", "Villard" },
		"grilled salmon",
		"personality coach",
		68112.00
		},
		{ { "Rodney", "Swillbelly" },
		"tripe",
		"tabloid editor",
		432400.00
		}
	};
	struct guy * him;    /* here is a pointer to a structure */

	printf("address #1: %p #2: %p\n", &fellow[0], &fellow[1]);
	him = &fellow[0];    /* tell the pointer where to point  */
	printf("pointer #1: %p #2: %p\n", him, him + 1);
	printf("him->income is $%.2f: (*him).income is $%.2f\n",
		him->income, (*him).income);
	him++;               /* point to the next structure      */
	printf("him->favfood is %s:  him->handle.last is %s\n",
		him->favfood, him->handle.last);

	return 0;
}

指针声明

指针访问成员

第一种：- >

第二种：（*him）.income

之前写过的程序的例子链接：PID
https://blog.csdn.net/answerMack/article/details/83900027

向函数传递结构的信息

函数与结构交互

传递结构成员

#include 
#define FUNDLEN 50

struct funds {
	char   bank[FUNDLEN];
	double bankfund;
	char   save[FUNDLEN];
	double savefund;
};

double sum(double, double);

int main(void)
{
	struct funds stan = {
		"Garlic-Melon Bank",
		4032.27,
		"Lucky's Savings and Loan",
		8543.94
	};

	printf("Stan has a total of $%.2f.\n",
		sum(stan.bankfund, stan.savefund));
	return 0;
}

/* adds two double numbers */
double sum(double x, double y)
{
	return(x + y);
}

传递结构地址

主函数：

sum(&stan)

求和函数

double sum(const struct funds * money)
{
	return(money->bankfund + money->savefund);
}

传递结构

主函数：

sum(stan)

求和函数

double sum(struct funds money)
{
	return(money.bankfund + money.savefund);
}

其他结构特性

使用指针：传递地址，且函数为void形式

#include 
#include 

#define NLEN 30
struct namect {
	char fname[NLEN];
	char lname[NLEN];
	int letters;
};

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;

	getinfo(&person);
	makeinfo(&person);
	showinfo(&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);
}

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');   // look for newline
		if (find)                  // if the address is not NULL,
			*find = '\0';          // place a null character there
		else
			while (getchar() != '\n')
				continue;          // dispose of rest of line
	}
	return ret_val;
}

使用结构：传递结构

#include 
#include 

#define NLEN 30
struct namect {
	char fname[NLEN];
	char lname[NLEN];
	int letters;
};

struct namect getinfo(void);
struct namect makeinfo(struct namect);
void showinfo(struct namect);
char * s_gets(char * st, int n);

int main(void)
{
	struct namect person;

	person = getinfo();
	person = makeinfo(person);
	showinfo(person);

	return 0;
}

struct namect getinfo(void)
{
	struct namect temp;
	printf("Please enter your first name.\n");
	s_gets(temp.fname, NLEN);
	printf("Please enter your last name.\n");
	s_gets(temp.lname, NLEN);

	return temp;
}

struct namect makeinfo(struct namect info)
{
	info.letters = strlen(info.fname) + strlen(info.lname);

	return info;
}

void showinfo(struct namect info)
{
	printf("%s %s, your name contains %d letters.\n",
		info.fname, info.lname, info.letters);
}

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');   // look for newline
		if (find)                  // if the address is not NULL,
			*find = '\0';          // place a null character there
		else
			while (getchar() != '\n')
				continue;          // dispose of rest of line
	}
	return ret_val;
}

函数定义中包含返回值，可以返回该结构。
函数声明：struct namect makeinfo(struct namect);

结构和结构指针选择

结构中的字符数组和字符指针

结构、指针和malloc()

malloc动态分配内存（详情见12章）与free函数相结合使用

#include 
#include    // for strcpy(), strlen()
#include    // for malloc(), free()
#define SLEN 81
struct namect {
	char * fname;  // using pointers
	char * lname;
	int letters;
};

void getinfo(struct namect *);        // allocates memory
void makeinfo(struct namect *);
void showinfo(const struct namect *);
void cleanup(struct namect *);        // free memory when done
char * s_gets(char * st, int n);

int main(void)
{
	struct namect person;

	getinfo(&person);
	makeinfo(&person);
	showinfo(&person);
	cleanup(&person);

	return 0;
}

void getinfo(struct namect * pst)
{
	char temp[SLEN];
	printf("Please enter your first name.\n");
	s_gets(temp, SLEN);
	// allocate memory to hold name
	pst->fname = (char *)malloc(strlen(temp) + 1);
	// copy name to allocated memory
	strcpy_s(pst->fname, strlen(temp)+1, temp);
	printf("Please enter your last name.\n");
	s_gets(temp, SLEN);
	pst->lname = (char *)malloc(strlen(temp) + 1);
	strcpy_s(pst->lname, strlen(temp)+1,temp);
}

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);
}

void cleanup(struct namect * 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');   // look for newline
		if (find)                  // if the address is not NULL,
			*find = '\0';          // place a null character there
		else
			while (getchar() != '\n')
				continue;          // dispose of rest of line
	}
	return ret_val;
}

复合字面量和结构（c99）

复合字面量可以不需要变量名！！

伸缩型数组成员（c99）

书本例程程序有错误（14.12）

#include 
#include 

struct flex
{
	size_t count;
	double average;
	double scores[];   // flexible array member
};

void showFlex(const struct flex * p);

int main(void)
{
	struct flex * pf1, *pf2;
	int n = 5;
	int i;
	int tot = 0;

	// allocate space for structure plus array
	pf1 = (struct flex *)malloc(sizeof(struct flex) + n * sizeof(double));
	pf1->count = n;
	for (i = 0; i < n; i++)
	{
		pf1->scores[i] = 20.0 - i;
		tot += pf1->scores[i];
	}
	pf1->average = tot / n;
	showFlex(pf1);

	n = 9;
	tot = 0;
	pf2 = (struct flex *)malloc(sizeof(struct flex) + n * sizeof(double));
	pf2->count = n;
	for (i = 0; i < n; i++)
	{
		pf2->scores[i] = 20.0 - i / 2.0;
		tot += pf2->scores[i];
	}
	pf2->average = tot / n;
	showFlex(pf2);
	free(pf1);
	free(pf2);

	return 0;
}

void showFlex(const struct flex * p)
{
	int i;
	printf("Scores : ");
	for (i = 0; i < p->count; i++)
		printf("%g ", p->scores[i]);
	printf("\nAverage: %g\n", p->average);
}

---

错误语句：
pf1 = (struct flex *)malloc(sizeof(struct flex) + n * sizeof(double));
pf2 = (struct flex *)malloc(sizeof(struct flex) + n * sizeof(double));
malloc应坚持使用强制类型转换！！！

---

结果：

匿名结构（c11）

使用结构数组的函数

#include 
#define FUNDLEN 50
#define N 2

struct funds {
	char   bank[FUNDLEN];
	double bankfund;
	char   save[FUNDLEN];
	double savefund;
};

double sum(const struct funds money[], int n);

int main(void)
{
	struct funds jones[N] = {
		{
			"Garlic-Melon Bank",
			4032.27,
		"Lucky's Savings and Loan",
		8543.94

		},
		{
			"Honest Jack's Bank",
			3620.88,
		"Party Time Savings",
		3802.91
		}
	};

	printf("The Joneses have a total of $%.2f.\n",
		sum(jones, N));

	return 0;
}

double sum(const struct funds money[], int n)
{
	double total;
	int i;

	for (i = 0, total = 0; i < n; i++)
		total += money[i].bankfund + money[i].savefund;

	return(total);
}

把结构内容保存到文件中（待理解+13章内容）

fprintf（见11章）

---

（文件操作见13章，本人未写）

fopen_s(&pbooks,“book.dat”, “a+b”)

---

#include 
#include 
#include 
#define MAXTITL  40
#define MAXAUTL  40
#define MAXBKS   10             /* maximum number of books */

char * s_gets(char * st, int n);

struct book {                   /* set up book template    */
	char title[MAXTITL];
	char author[MAXAUTL];
	float value;
};

int main(void)
{
	struct book library[MAXBKS]; /* array of structures     */
	int count = 0;
	int index, filecount;
	FILE * pbooks;
	int size = sizeof(struct book);

	if ((fopen_s(&pbooks,"book.dat", "a+b")) == NULL)
	{
		fputs("Can't open book.dat file\n", stderr);
		exit(1);
	}

	rewind(pbooks);            /* go to start of file     */
	while (count < MAXBKS &&  fread(&library[count], size,
		1, pbooks) == 1)
	{
		if (count == 0)
			puts("Current contents of book.dat:");
		printf("%s by %s: $%.2f\n", library[count].title,
			library[count].author, library[count].value);
		count++;
	}
	filecount = count;
	if (count == MAXBKS)
	{
		fputs("The book.dat file is full.", stderr);
		exit(2);
	}

	puts("Please add new book titles.");
	puts("Press [enter] at the start of a line to stop.");
	while (count < MAXBKS && s_gets(library[count].title, MAXTITL) != NULL
		&& library[count].title[0] != '\0')
	{
		puts("Now enter the author.");
		s_gets(library[count].author, MAXAUTL);
		puts("Now enter the value.");
		scanf_s("%f", &library[count++].value);
		while (getchar() != '\n')
			continue;                /* clear input line  */
		if (count < MAXBKS)
			puts("Enter the next title.");
	}

	if (count > 0)
	{
		puts("Here is the list of your books:");
		for (index = 0; index < count; index++)
			printf("%s by %s: $%.2f\n", library[index].title,
				library[index].author, library[index].value);
		fwrite(&library[filecount], size, count - filecount,
			pbooks);
	}
	else
		puts("No books? Too bad.\n");

	puts("Bye.\n");
	fclose(pbooks);

	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');   // look for newline
		if (find)                  // if the address is not NULL,
			*find = '\0';          // place a null character there
		else
			while (getchar() != '\n')
				continue;          // dispose of rest of line
	}
	return ret_val;
}

---

把//exit(1);注释掉了的下面结果：

链式结构（简介，内容少）

联合简介（union）

用法

匿名联合（c11）

结构和union运算符

枚举类型enum

enum常量为int类型。

用法

#include 
#include     // for strcmp(), strchr()
#include    // C99 feature
char * s_gets(char * st, int n);

enum spectrum { red, orange, yellow, green, blue, violet };
const char * colors[] = { "red", "orange", "yellow",
"green", "blue", "violet" };
#define LEN 30

int main(void)
{
	char choice[LEN];
	int  color;
	bool color_is_found = false;

	puts("Enter a color (empty line to quit):");
	while (s_gets(choice, LEN) != NULL && choice[0] != '\0')
	{
		for (color = red; color <= violet; color++)
		{
			if (strcmp(choice, colors[color]) == 0)
			{
				color_is_found = true;
				break;
			}
		}
		if (color_is_found)
			switch (color)
			{
			case red: puts("Roses are red.");
				break;
			case orange: puts("Poppies are orange.");
				break;
			case yellow: puts("Sunflowers are yellow.");
				break;
			case green: puts("Grass is green.");
				break;
			case blue: puts("Bluebells are blue.");
				break;
			case violet: puts("Violets are violet.");
				break;
			}
		else
			printf("I don't know about the color %s.\n", choice);
		color_is_found = false;
		puts("Next color, please (empty line to quit):");
	}
	puts("Goodbye!");

	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');   // look for newline
		if (find)                  // if the address is not NULL,
			*find = '\0';          // place a null character there
		else
			while (getchar() != '\n')
				continue;          // dispose of rest of line
	}
	return ret_val;
}

---

把enum spectrum color改为了int color

---

共享名称空间

typedef简介

typedef和#define

其他复杂声明（指针和数组的解释※※重要）

复杂声明：*、（）、[]

函数类复杂声明

typedef建立的声明

函数和指针

// func_ptr.c -- uses function pointers
#include 
#include 
#include 
#define LEN 81

char * s_gets(char * st, int n);

char showmenu(void);
void eatline(void);     // read through end of line

void show(void(*fp)(char *), char * str);//函数指针

void ToUpper(char *);   // convert string to uppercase
void ToLower(char *);   // convert string to uppercase
void Transpose(char *); // transpose cases
void Dummy(char *);     // leave string unaltered

int main(void)
{
	char line[LEN];
	char copy[LEN];
	char choice;

	//函数指针
	void(*pfun)(char *); // points a function having a
						 // char * argument and no
						 // return value
	

	puts("Enter a string (empty line to quit):");

	while (s_gets(line, LEN) != NULL && line[0] != '\0')
	{
		while ((choice = showmenu()) != 'n')
		{
			switch (choice)  // switch sets pointer
			{
			case 'u': pfun = ToUpper;   break;
			case 'l': pfun = ToLower;   break;
			case 't': pfun = Transpose; break;
			case 'o': pfun = Dummy;     break;
			}
			strcpy_s(copy, line);// make copy for show()
			show(pfun, copy);  // use selected function
		}
		puts("Enter a string (empty line to quit):");
	}
	puts("Bye!");

	return 0;
}

char showmenu(void)
{
	char ans;
	puts("Enter menu choice:");
	puts("u) uppercase       l) lowercase");
	puts("t) transposed case o) original case");
	puts("n) next string");

	ans = getchar();    // get response
	ans = tolower(ans); // convert to lowercase
	eatline();          // dispose of rest of line
	while (strchr("ulton", ans) == NULL)
	{
		puts("Please enter a u, l, t, o, or n:");
		ans = tolower(getchar());
		eatline();
	}

	return ans;
}

void eatline(void)
{
	while (getchar() != '\n')
		continue;
}

void ToUpper(char * str)
{
	while (*str)
	{
		*str = toupper(*str);
		str++;
	}
}

void ToLower(char * str)
{
	while (*str)
	{
		*str = tolower(*str);
		str++;
	}
}
void Transpose(char * str)
{
	while (*str)
	{
		if (islower(*str))
			*str = toupper(*str);
		else if (isupper(*str))
			*str = tolower(*str);
		str++;
	}
}

void Dummy(char * str)
{
	// leaves string unchanged
}

void show(void(*fp)(char *), char * str)
{
	(*fp)(str); // apply chosen function to str
	puts(str);  // display result
}

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');   // look for newline
		if (find)                  // if the address is not NULL,
			*find = '\0';          // place a null character there
		else
			while (getchar() != '\n')
				continue;          // dispose of rest of line
	}
	return ret_val;
}

总结

关键概念

小结

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2020-04-24 大连

（看的有些匆忙，可能太粗糙了，大多粘粘与截图，这个结构自己之前参考别人的写过，所有看这些理论能够懂得更快一些，如果其他人看到，建议自己看看书或者教学视频！！！）加油！！！ 13章的文件处理个人可能不更，想学自己翻翻书！！！！！

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