以下代码在运行时生成分段错误。。。只是因为我试着使用p_list3(二级指针(打印其内容或为其分配一些内容
注意：注意每个代码段中的printf(...)差异
完整的代码在末尾
struct node **p_list2 = NULL, **p_list3 = NULL;
p_list = &list;
while((*p_list)->next != NULL) //Start [[WHILE1]]
{
p_list2 = &(*p_list)->next;
while(*p_list2 != NULL) //start [[WHILE2]]
{
printf("%s %s %un", (*p_list)->word, (*p_list2)->word, p_list3);
p_list2 = &(*p_list2)->next;
} //End [[WHILE2]]
p_list3 = p_list;
p_list = &(*p_list)->next;
} //End [[WHILE1]]
而这个
struct node **p_list2 = NULL, **p_list3 = NULL;
p_list = &list;
while((*p_list)->next != NULL) //Start [[WHILE1]]
{
p_list2 = &(*p_list)->next;
while(*p_list2 != NULL) //start [[WHILE2]]
{
printf("%s %s n", (*p_list)->word, (*p_list2)->word);
p_list2 = &(*p_list2)->next;
} //End [[WHILE2]]
p_list3 = p_list;
p_list = &(*p_list)->next;
} //End [[WHILE1]]
也没有这个
struct node **p_list2 = NULL, **p_list3 = NULL;
p_list = &list;
while((*p_list)->next != NULL) //Start [[WHILE1]]
{
p_list2 = &(*p_list)->next;
while(*p_list2 != NULL) //start [[WHILE2]]
{
printf("%s %s %un", (*p_list)->word, (*p_list2)->word, p_list3);
p_list2 = &(*p_list2)->next;
} //End [[WHILE2]]
//p_list3 = p_list;
p_list = &(*p_list)->next;
} //End [[WHILE1]]
不会产生这样的错误。。这里发生了什么？？？
完整代码
/*
@@@@ PROGRAM NAME: knkcch17proj05.c
@@@@ FLAGS: -std=c99
@@@@ PROGRAM STATEMENT:
Write a program that sorts a series of words
entered by the user:
Enter word: foo
Enter word: bar
Enter word: baz
Enter word: quux
Enter word:
In sorted order: bar baz foo quux
Assume that each word is no more than 20 characters long. Stop reading when the
user enters an empty word (i.e., presses Enter without entering a word). Store
each word in a dynamically allocated string, using an array of pointers to keep
track of the strings, as in the remind2.c program (Section 17.2). After all
words have been read, sort the array (using any sorting technique) and then use
a loop to print the words in sorted order. Hint: Use the read_line function to
read each word, as in remind2.c.
*/
#include <stdio.h>
#include <string.h> //strcpy()
#include <stdlib.h> //malloc(), free(), NULL, EXIT_FAILURE
#include <ctype.h> //isspace()
//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------
struct node
{
char word[10];
struct node *next;
} *list = NULL;
//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------
int read_line(char str[], int n);
//------------------------START OF MAIN()--------------------------------------
int main(void)
{
printf("++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++n");
printf("File: %s, C Version: %ld, Date: %s, Time: %snn", __FILE__, __STDC_VERSION__, __DATE__, __TIME__);
char *str;
struct node **p_list = &list, *new_word;
//Get words from user
while(1)
{
printf("Enter word: ");
//Allocate memory of size about struct node + 10 bytes
if((new_word = (struct node *)malloc(sizeof(struct node))) == NULL)
{
printf("Error: malloc failed.");
exit(EXIT_FAILURE);
}
//Read word
(read_line(str, 10));
if(!strlen(str)) //If 'n' is detected without reading character.
break;
//Read word is stored to node.
strcpy(new_word->word, str);
new_word->next = NULL;
//Load the node to list
*p_list = new_word;
p_list = &(*p_list)->next;
}
//Print words in the order they entered
printf("nIn Unsorted order: ");
new_word = list;
while(new_word)
{
printf("%s ", new_word->word);
new_word = new_word->next;
}
//Sorting
struct node **p_list2 = NULL, **p_list3 = NULL;
p_list = &list;
while((*p_list)->next != NULL) //Start [[WHILE1]]
{
p_list2 = &(*p_list)->next;
while(*p_list2 != NULL) //start [[WHILE2]]
{
printf("%u %u %un", p_list, p_list2, p_list3);
printf("%s %s %un", (*p_list)->word, (*p_list2)->word, p_list3);
#if 0
if((strcmp((*p_list)->word, (*p_list2)->word)) == 1) //Start [[IF1]]
{
printf("%s %sn", (*p_list)->word, (*p_list2)->word);
if(p_list3 != NULL)
(*p_list3)->next = *p_list2; //update previous node.
(*p_list)->next = (*p_list2)->next;
(*p_list2)->next = *p_list;
struct node *temp = *p_list;
*p_list = *p_list2;
*p_list2 = temp;
} //End [[IF1]]
#endif
p_list2 = &(*p_list2)->next;
} //End [[WHILE2]]
p_list3 = p_list;
p_list = &(*p_list)->next;
} //End [[WHILE1]]
printf("nIn sorted order: ");
new_word = list;
while(list)
{
//print the word
printf("%s ", list->word);
//prepare to free the allocated memory
new_word = list;
list = list->next;
//free the memory.
free(new_word);
}
printf("n++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++n");
return 0;
}
//-------------------------END OF MAIN()---------------------------------------
int read_line(char str[], int n)
{
int ch, i = 0;
//while (isspace(ch = getchar()))
//;
ch = getchar();
while (ch != 'n' && ch != EOF) {
if (i < n)
str[i++] = ch;
ch = getchar();
}
str[i] = ' ';
return i;
}
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
@Yaachaka我将非常狭隘地回答你的问题，只是解决分段错误的原因，不要评论程序是否有效。
崩溃的原因是，在对read_line的调用中，您正在为str:传递一个未初始化的值
char *str;
struct node **p_list = &list, *new_word;
//Get words from user
while(1)
{
printf("Enter word: ");
//Allocate memory of size about struct node + 10 bytes
if((new_word = (struct node *)malloc(sizeof(struct node))) == NULL)
{
printf("Error: malloc failed.");
exit(EXIT_FAILURE);
}
//Read word
(read_line(str, 10));
if(!strlen(str)) //If 'n' is detected without reading character.
break;
//Read word is stored to node.
strcpy(new_word->word, str);
new_word->next = NULL;
这是一个问题，因为read_line期望第一个参数指向可以存储正在读取的行的位置。假设您已经有一个未使用的缓冲区(new_word->word(，您可以通过将上面的代码更改为直接读取到new_node->中来修复崩溃；单词：
struct node **p_list = &list, *new_word;
//Get words from user
while(1)
{
printf("Enter word: ");
//Allocate memory of size about struct node + 10 bytes
if((new_word = (struct node *)malloc(sizeof(struct node))) == NULL)
{
printf("Error: malloc failed.");
exit(EXIT_FAILURE);
}
//Read word
(read_line(new_word->word, 10));
if(!strlen(new_word->word)) { //If 'n' is detected without reading character.
free(new_word);
break;
}
new_word->next = NULL;
指针就是所需的全部str没有分配内存，char str[21];将工作read_line()需要使用if (i < n - 1)来确保终止零点在数组边界内
为了简单起见，每个新词都会添加到列表的开头。
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
struct node
{
char word[21];
struct node *next;
};
int read_line(char str[], int n);
int main(void)
{
printf("++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++n");
printf("File: %s, C Version: %ld, Date: %s, Time: %snn", __FILE__, __STDC_VERSION__, __DATE__, __TIME__);
char str[21];
struct node *p_list = NULL;
struct node *new_word = NULL;
//Get words from user
while(1)
{
printf("Enter word: ");
//Read word
read_line ( str, 21);
if ( ! strlen ( str)) { //If 'n' is detected without reading character.
break;
}
if ( ( new_word = malloc ( sizeof *new_word)) == NULL)
{
printf("Error: malloc failed.");
exit(EXIT_FAILURE);
}
//Read word is stored to node.
strcpy ( new_word->word, str);
//Load the node to beginning of list
new_word->next = p_list;
p_list = new_word;
}
//Print words in the reversed order they entered
printf("nIn Unsorted order: ");
new_word = p_list;
while ( new_word)
{
printf("%s ", new_word->word);
new_word = new_word->next;
}
printf("n");
//Sorting
struct node *p_list2 = p_list;
struct node *p_list3 = p_list;
struct node *sort = p_list;
while ( sort->next != NULL) //Start [[WHILE1]]
{
p_list2 = sort->next;
while ( p_list2 != NULL) //start [[WHILE2]]
{
printf("%s %s %pn", sort->word, p_list2->word, (void *)p_list3);
p_list2 = p_list2->next;
} //End [[WHILE2]]
sort = sort->next;
p_list3 = sort;
} //End [[WHILE1]]
printf("nIn sorted order: ");
new_word = p_list;
while( new_word)
{
printf("%s ", new_word->word);
new_word = new_word->next;
}
new_word = p_list;
while( new_word) {
p_list = new_word;
new_word = p_list->next;
//free the memory.
free( p_list);
}
printf("n++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++n");
return 0;
}
//-------------------------END OF MAIN()---------------------------------------
int read_line(char str[], int n)
{
int ch, i = 0;
while ( ( ch = getchar ( )) != 'n' && ch != EOF) {
if (i < n - 1) {// - 1 to provide for terminating zero
str[i++] = ch;
}
}
str[i] = ' ';
return i;
}