瓦尔格林德·马洛克和寻找邪恶段错误的探索

Question

下面是我的代码，然后是Valgrind的txt。我不知道为什么这么久，超级抱歉。我真的是新人。请帮助我理解为什么编译时没有错误消息但程序失败？我知道这是某个地方的记忆泄漏，但我处于智慧的尽头。在下面的混乱中，我应该寻找什么？

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
// customer record
typedef char customerName[9];
typedef struct customer {
customerName name;                  // 1-9 upper case letters
int lineNumber;                     // line number customer gets on
int time;                           // arrival time at line
int numberItems;                    // number of items customer has
} customer;
// [singly linked] queue element
typedef customer *qitem;
typedef struct node {
qitem data;                         // pointer to actual data
struct node *next;                  // forward pointer to next item
} node;
// queue definition (singly linked list)
// NOTE:
typedef struct queue {
node *front;                        // pointer to first node in list ie front of line with cashier
} queue;
// qinit -- initialize/reset queue
void qinit(queue *q)
{
q->front = NULL;
}
// qempty -- returns 1 if empty or 0 if false
int qempty(queue *q)
{
return (q->front == NULL);
}
// enqueue -- append element to end of queue
void enqueue(queue *q, qitem data)
{
node *newnode;
node *prev;
newnode = malloc(sizeof(node));
newnode->next = NULL;
newnode->data = data;
// find the back of the queue with only a front pointer
prev = NULL;
for (node *cur = q->front;  cur != NULL;  cur = cur->next)
prev = cur;
// append to tail of list
if (prev != NULL)
prev->next = newnode;
// add to end of empty list
else
q->front = newnode;
}
// dequeue -- dequeue from the front of the queue
qitem dequeue(queue *q)
{
node *curnode;
qitem data;
do {
curnode = q->front;
// bug out if list is empty
if (curnode == NULL) {
data = NULL;
break;
}
// get node's data value (e.g. pointer to customer struct)
data = curnode->data;
// release the node's storage back to the heap
free(curnode);
} while (0);
return data;
}
// qfront -- peek at front of queue
qitem qfront(queue *q)
{
node *curnode;
qitem data;
curnode = q->front;
if (curnode != NULL)
data = curnode->data;
else
data = NULL;
return data;
}

int main(int argc, const char * argv[]) {
int testCases = 0;
scanf("%d", &testCases);
if(testCases > 0 && testCases <= 25){//shortcircuiting???
while (testCases--){
queue *q;
q = malloc(sizeof(queue));
qinit(q);// starting new queue
int numCustomers;
scanf("%d", &numCustomers);
if(numCustomers < 0 || numCustomers > 11){
return 0;
}
queue* customerArray = (queue*) malloc(sizeof(queue) * 12);
for ( int i = 0; i < numCustomers; i++){
customer* newCustomer = (customer*) malloc(sizeof(customer));
scanf("%d", &(newCustomer->time));
scanf("%d", &(newCustomer->lineNumber));
scanf("%s", newCustomer->name);
scanf("%d", &(newCustomer->numberItems));
enqueue(&customerArray[newCustomer->lineNumber - 1], newCustomer);
}

int totalTime = INT_MAX;
for(int i=0;i<12;i++)
{
customer* frontCustomer = qfront(&customerArray[i]);
if(totalTime < frontCustomer->time)
{
totalTime = frontCustomer->time;
}
free(frontCustomer);
}
while(numCustomers--) {
int customerToCheckOutLine = 0; int minNumberOfItems = INT_MAX;
for( int j=11 ; j>=0; j--){
customer* frontCustomer = qfront(&customerArray[j]);
if(frontCustomer->time <= totalTime)
{
if(frontCustomer->numberItems < minNumberOfItems)
{
customerToCheckOutLine = frontCustomer->lineNumber;
minNumberOfItems = frontCustomer->numberItems;
}
free(frontCustomer);
}
}

customer* customerToCheckOut = qfront(&customerArray[customerToCheckOutLine -1 ]);
totalTime += 30;
totalTime += (customerToCheckOut->numberItems) * 5;
dequeue(&customerArray[customerToCheckOutLine - 1]);
}
free(customerArray);
}
}
return 0;
}

样本在

阿拉伯数字 5 10 1史蒂文12 12 6 艾哈迈德 8 13 1珍妮40 22 6 杰梅因 39 100000 12 阿玛利亚 53 6 100 1 A 100 200 2 字节 99 300 3 C 98 400 4 D 97 500 5 E 96 600 6 F 95

Answer 1

到达这条线时

// release the node's storage back to the heap
free(curnode);

队列中有一个指向currnode的活动指针。下次调用队列函数时，它将尊重该指针。您需要在dequeue()中调整队列的内容。

Answer 2

我发现了两个错误：

queue* customerArray = (queue*) malloc(sizeof(queue) * 12);
for ( int i = 0; i < numCustomers; i++){
// ...
enqueue(&customerArray[newCustomer->lineNumber - 1], newCustomer);
}

customerArray中的队列永远不会初始化，因此它们的front指针可能包含垃圾，从而导致enqueue崩溃。

customer* frontCustomer = qfront(&customerArray[i]);
if(totalTime < frontCustomer->time)
{
totalTime = frontCustomer->time;
}
free(frontCustomer);
}

如果特定队列中没有元素，则frontCustomer可能为 null。 如果发生这种情况，frontCustomer->time将取消引用空指针并崩溃。