为什么会出现段错误？

lluct

该列队链接能正确的编译运行完，但在运行完之后出现一个"段错误"，为什么？

1. 
   
2. #include <stdio.h>
   
3. 
   
4. typedef struct linked_queue
   
5. {
   
6.   int data;
   
7.   struct linked_queue *next;
   
8. } LqueueTp;
   
9. 
   
10. typedef struct queueptr
    
11. {
    
12.   LqueueTp *front, *rear;
    
13. } QueptrTp;
    
14. 
    
15. int main()
    
16. {
    
17.   QueptrTp *lq;
    
18.   int input;
    
19.   int i = 0;
    
20.   int outnum;
    
21. 
    
22.   InitQueue(&lq);
    
23.   printf("请输入一些数字:");
    
24.   scanf("%d", &input);
    
25.   while (input != 0)
    
26.     {
    
27.       EnQueue(&lq, input);
    
28.       scanf("%d", &input);
    
29.     }
    
30.   GetHead(&lq, &input);
    
31.   printf("当前链接列队的队头为:%d", input);
    
32.   printf("\n请输入要出队的个数:");
    
33.   scanf("%d", &outnum);
    
34.   printf("依此出队的数为:");
    
35.   while (i < outnum)
    
36.     {
    
37.       OutQueue(&lq, &input);
    
38.       printf("%d ", input);
    
39.       i++;
    
40.     }
    
41.   printf("\n当前列队排列:");
    
42.   while (! EmptyQueue(&lq))
    
43.     {
    
44.       OutQueue(&lq, &input);
    
45.       printf("%d ", input);
    
46.     }
    
47.   printf("\n\n");
    
48. }
    
49. 
    
50. int InitQueue (QueptrTp **lq)
    
51. {
    
52.   LqueueTp *p;
    
53.   p = (LqueueTp *) malloc (sizeof(LqueueTp));
    
54.   (*lq) -> front = p;
    
55.   (*lq) -> rear = p;
    
56.   ((*lq) -> front)  -> next = NULL;
    
57. }
    
58. 
    
59. int EnQueue (QueptrTp **lq, int x)
    
60. {
    
61.   LqueueTp *p;
    
62.   p = (LqueueTp *) malloc (sizeof(LqueueTp));
    
63.   p -> data = x;
    
64.   p -> next = NULL;
    
65.   ((*lq) -> rear) -> next = p;
    
66.   (*lq) -> rear = p;
    
67. }
    
68. 
    
69. int OutQueue (QueptrTp **lq, int *x)
    
70. {
    
71.   LqueueTp *s;
    
72.   if ((*lq) -> front == (*lq) -> rear)
    
73.     {
    
74.       printf("队空!\n");
    
75.       return 0;
    
76.     }
    
77.   else
    
78.     {
    
79.     s = ((*lq) -> front) -> next;
    
80.     *x = s -> data;
    
81.     ((*lq) -> front) -> next = s -> next;
    
82.     if (s -> next == NULL)
    
83.       (*lq) -> rear = (*lq) -> front;
    
84.     free(s);
    
85.     return 1;
    
86.     }
    
87. }
    
88. 
    
89. int EmptyQueue (QueptrTp **lq)
    
90. {
    
91.   if (((*lq) -> rear) == ((*lq) -> front))
    
92.     return 1;
    
93.   else
    
94.     return 0;
    
95. }
    
96. 
    
97. int GetHead (QueptrTp **lq, int *x)
    
98. {
    
99.   LqueueTp *p;
    
100.   if ((*lq) -> rear == (*lq) -> front)
     
101.     return 0;
     
102.   else
     
103.     {
     
104.       p = ((*lq) -> front ) -> next;
     
105.       *x = p -> data;
     
106.       return 1;
     
107.     }
     
108. }
     
109. 
     

复制代码

pupilzeng

出现段错误是因为访问了不能访问的内存空间。

wide288

找找吧，内存，变量定义或使用的问题。等等

chice

i haven't compile your program,

but .... such code is dangerous, it may crash your program.
p = ((*lq) -> front ) -> next;

you should use the following code:
if( *lq )
  if( (*lq)->front )
     p = ((*lq) -> front ) -> next;

romy

QueptrTp *lq;
这个lq没初始化。

romy

另外：
InitQueue等函数的参数不必要使用QueptrTp **类型，
用QueptrTp * 就足够了

kj501

段错误是lq没有初始化就使用造成的。