Question

我编译了一次文件，并使用相同的输出运行它，并且我只有大约20-30％的时间得到分段错误。我只是通过电子邮件发送给我的教授，但她正在服用。我真的不知道为什么，特别是因为错误不会一直发生，但有时只有完全相同的a.out文件。我确切地知道错误发生的位置，来自if（sDB [index] == 0）。

感谢您的帮助，

如果需要更多代码来解决问题，请告诉我。

* sDB是我的构造函数中初始化的指针数组：

*sDB = new HashElem[MAX];

结构：

struct Elem { 
    student *info;
    Elem *next;
};

struct HashElem {
    student *info;
    HashElem *next; 
};

我的代码片段：

void studentsDB::push( student *std ) {

Elem *e = new Elem;
e->info = std;

Elem *cur = head;
while( cur->next != 0 ) 
    cur = cur->next;

cur->next = e;
e->next = 0;

int index = std->hash( );

HashElem *h = new HashElem;
h->info = std;;
if( sDB[index] == 0 ) { //<<< THIS LINE CAUSES THE ERROR
    sDB[index] = h; 
    h->next = 0;
}
else {
    HashElem *ha = sDB[index];
    while( ha->next != 0 ) {
        ha = ha->next;
    }
    ha->next = h;
}

size++;
}

散列（）：

int student::hash( ) {
int ret = 0;
string s = id;

for( int i = 0; i < s.length( ); i++ )
    ret = 33 * ret + s[i];

return ret % MAX;
}

输出：

bash-4.2$ g++ *.cpp
bash-4.2$ ./a.out students.dat courses.dat 
begin
objects created
+++ Before the if statement +++
+++ 548 +++
Segmentation fault

bash-4.2$ ./a.out students.dat courses.dat 
begin
objects created
+++ Before the if statement +++
+++ 548 +++
Segmentation fault

bash-4.2$ ./a.out students.dat courses.dat 
begin
objects created
+++ Before the if statement +++
+++ 548 +++
+++ After +++
+++ Before the if statement +++
+++ 626 +++
+++ After +++
+++ Before the if statement +++
+++ 605 +++
+++ After +++
+++ Before the if statement +++
+++ 915 +++
+++ After +++
+++ Before the if statement +++
+++ 915 +++
printList
Flintstone, Fred 000-12SA 3 121314 12333 12116 
Flintstone, Wilma 000-45SA 2 12332 12111 
Glotz, Joe Q 901-9984 3 12332 12116 12111 
Rubble, Barney 001-01SA 3 121314 12111 12116 
CS001 1 12111 1 10 3 000-45SA 901-9984 001-01SA 
CS515 2 121314 4 45 2 000-12SA 001-01SA 
CH302 1 12116 5 15 3 000-12SA 901-9984 001-01SA 
MA111 1 12333 4 15 1 000-12SA 
PH999 1 12999 2 10 0000-12SA901-9984 
PY000 3 12332 6 5 2 000-45SA 901-9984 

bash-4.2$ ./a.out students.dat courses.dat 
begin
objects created
+++ Before the if statement +++
+++ 548 +++
Segmentation fault

bash-4.2$ ./a.out students.dat courses.dat 
begin
objects created
+++ Before the if statement +++
+++ 548 +++
Segmentation fault

bash-4.2$ ./a.out students.dat courses.dat 
begin
objects created
+++ Before the if statement +++
+++ 548 +++
+++ After +++
+++ Before the if statement +++
+++ 626 +++
+++ After +++
+++ Before the if statement +++
+++ 605 +++
+++ After +++
+++ Before the if statement +++
+++ 915 +++
+++ After +++
+++ Before the if statement +++
+++ 915 +++
printList
Flintstone, Fred 000-12SA 3 121314 12333 12116 
Flintstone, Wilma 000-45SA 2 12332 12111 
Glotz, Joe Q 901-9984 3 12332 12116 12111 
Rubble, Barney 001-01SA 3 121314 12111 12116 
CS001 1 12111 1 10 3 000-45SA 901-9984 001-01SA 
CS515 2 121314 4 45 2 000-12SA 001-01SA 
CH302 1 12116 5 15 3 000-12SA 901-9984 001-01SA 
MA111 1 12333 4 15 1 000-12SA 
PH999 1 12999 2 10 0000-12SA901-9984 
PY000 3 12332 6 5 2 000-45SA 901-9984 

bash-4.2$ ./a.out students.dat courses.dat 
begin
objects created
+++ Before the if statement +++
+++ 548 +++
+++ After +++
+++ Before the if statement +++
+++ 626 +++
+++ After +++
+++ Before the if statement +++
+++ 605 +++
+++ After +++
+++ Before the if statement +++
+++ 915 +++
Segmentation fault

gdb输出：

Starting program: /home/csu/dtk24/cs515/prog11/a.out students.dat courses.dat
begin
objects created
+++ Before the if statement +++
+++ 548 +++

Program received signal SIGSEGV, Segmentation fault.
0x0804b2a0 in studentsDB::push (this=0xbffff78c, std=0x8054120)
    at studentsDB.cpp:130
130     if( sDB[index] == 0 ) {

Answer 1

您的问题中没有足够的代码可以确定问题是什么。

然而，如果我冒险猜测，那么问题很可能是在hash（）中 - 这取决于你如何进行计算最终得到一个负数，或者一个大于哈希表的最大值的数< / p>

Answer 2

你写了一个双“;”字符。错误是在if。之前的行引起的。

随机分段故障C ++

2 个答案: