c - 收到 SIGSEGV 错误。找不到负责的指针

Question

我刚刚开始研究 C 中的链表，我似乎在打印部分遇到了无限循环，尝试修复仍然遇到相同问题的所有 Unresolved 问题。我已经尝试调试多次，但始终是 SIGSEGV 错误。我使用过 DEV C++ 和 GCC 4.9.2。

#include<stdio.h>
#include<stdlib.h>

typedef struct node {
    int data;
    struct node *next;
}node;

void print();
node *clist(int n);
node *head = NULL;

int main() 
{
    int n;
    printf("Input the number of nodes for the Linked List.\n");
    scanf("%d", &n);

    clist(n);
    print();

    return 0;
}

void print() 
{
    node *show = NULL;
    show = head;
    while (show != NULL) {
        printf("%d => ", show->data);  
        show = (show->next);
    }

    printf("NULL");

}

node *clist(int n) 
{
    node *temp = NULL;
    node *p = NULL;
    int i;

    for (i = 0; i<n; i++)
    {
        temp = (node*)malloc(sizeof(node));

        printf("Enter the element %d of the list", i + 1);
        scanf("%d", &temp->data);

        if (head == NULL)
        {
            head = temp;

        }

        else { 
      p = head; 
      while( p->next ) 
           { 
              p = p->next; 
            } 
            p->next = temp; //UPDATE: SIGSSEGV ERROR HERE NOW 
            }
              }
    return head;
}

Answer 1

以下建议代码:

1. 干净地编译
2. 执行所需的功能
3. 正确检查并处理错误
4. 始终缩进
5. 自行清理
6. 避免语句中的冗余，例如:if( head == NULL )
7. 消除未使用的返回值
8. 正确声明不带参数的函数原型(prototype)
9. 为了便于阅读，使用适当的水平间距

现在，建议的代码:

#include <stdio.h>
#include <stdlib.h>

typedef struct snode
{
    int data;
    struct snode *next;
} node;

// prototypes
void  print( void );
void  clist( int n );
void  cleanup( void );

node *head = NULL;


int main( void )
{
    int n;

    printf( "Input the number of nodes for the Linked List.\n" );
    if( scanf( "%d", &n ) != 1 )
    {
        fprintf( stderr, "scanf for number of data points failed\n" );
        exit( EXIT_FAILURE );
    }

    clist( n );
    print();
    cleanup();
    return 0; // << optional in modern C
}


void print()
{   
    node *show = head;

    while( show )
    {
        printf( "%d => ", show->data );
        show = show->next;
    }

    puts( "" );
}


void clist( int n )
{
    node *temp = NULL;
    node *p = NULL;

    for( int i=0; i<n; i++ )
    {
        temp = malloc( sizeof( node ) );
        if( !temp )
        {
            perror( "malloc failed" );
            cleanup();
            exit( EXIT_FAILURE );
        }

        // EDIT:
        temp->next = NULL;
        // end EDIT:

        printf( "Enter the element %d of the list", i+1 );
        if( scanf( "%d", &temp->data ) != 1 )
        {
            fprintf( stderr, "scanf for a data failed\n" );
            cleanup();
            exit( EXIT_FAILURE );
        }

        if( !head )
        {  // list empty
            head = temp;
        }

        else
        {  // list already contains some nodes
            p = head;

            while( p->next )
            {
                p = p->next;
            }
            p->next = temp;
        }
    }
}


void cleanup()
{
    node *temp = head;
    node *current;

    while( temp )
    {
        current = temp;
        temp = temp->next;
        free( current );
    }
}

这是程序简单运行的输出:

Input the number of nodes for the Linked List.
2
Enter the element 1 of the list1
Enter the element 2 of the list2
1 => 2 => 

建议在输出中的节点数据值的用户输入之前放置一个空格