《C Primer Plus（第六版）中文版》实践中发现的错误

《C Primer Plus（第六版）中文版》实践中发现的错误

一.1.书-17.2从数组到链表

用链表而不是数组来储存电影信息

书中的源代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define TSIZE 45
struct film {
    
    
	char title[TSIZE];
	int rating;
	struct film* next;
};
char* s_gets(char* st, int n);
int main(void)
{
    
    
	struct film* head = NULL;
	struct film* prev, * current;
	char input[TSIZE];
	puts("Enter first movie title:");
	while (s_gets(input, TSIZE) != NULL && input[0] != '\0')
	{
    
    
		current = (struct film*)malloc(sizeof(struct film));
		if (head == NULL)
			head = current;
		else
			prev->next = current;
		current->next = NULL;
		strcpy_s(current->title,input);
		puts("Enter your rating <0-10>:");
		scanf_s("%d",&current->rating);
		while (getchar() != '\n')
			continue;
		puts("Enter next movie title (empty line to stop):");
		prev = current;
	}
	if (head == NULL)
		printf("No data entered.");
	else
		printf("Here is the movie list:\n");
	current = head;
	while(current!=NULL)
	{
    
    
		printf("Movie: %s Rating: %d\n",
			current->title,current->rating);
		current = current->next;
	}
	current = head;
	while (current != NULL)
	{
    
    
		free(current);
		head = current->next;
	}
	printf("Bye!\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');
		if (find)
			*find = '\0';
		else
			while (getchar() != '\n')
				continue;
	}
	return ret_val;
}

2.实践

发现第一个细节错误，prev未进行初始化；
修改之后再来！

struct film* prev=NULL, * current;

给prev一个空指针常量
再来一次


发现
Bye!也没有输出
发现是释放已分配的内存时出错了
经过修改

while (current != NULL)
	{
    
    	
		head = current->next;
		free(current);
		current = head;
	}

3.再次实践

经过修改后 程序能正常运行！

4.完善后的源代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define TSIZE 45
struct film {
    
    
	char title[TSIZE];
	int rating;
	struct film* next;
};
char* s_gets(char* st, int n);
int main(void)
{
    
    
	struct film* head = NULL;
	struct film* prev=NULL, * current;
	char input[TSIZE];
	puts("Enter first movie title:");
	while (s_gets(input, TSIZE) != NULL && input[0] != '\0')
	{
    
    
		current = (struct film*)malloc(sizeof(struct film));
		if (head == NULL)
			head = current;
		else
			prev->next = current;
		current->next = NULL;
		strcpy_s(current->title,input);
		puts("Enter your rating <0-10>:");
		scanf_s("%d",&current->rating);
		while (getchar() != '\n')
			continue;
		puts("Enter next movie title (empty line to stop):");
		prev = current;
	}
	if (head == NULL)
		printf("No data entered.");
	else
		printf("Here is the movie list:\n");
	current = head;
	while(current!=NULL)
	{
    
    
		printf("Movie: %s Rating: %d\n",
			current->title,current->rating);
		current = current->next;
	}
	current = head;
	while (current != NULL)
	{
    
    	
		head = current->next;
		free(current);
		current = head;
	}
	printf("Bye!\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');
		if (find)
			*find = '\0';
		else
			while (getchar() != '\n')
				continue;
	}
	return ret_val;
}