c - VALGRIND MALLOC 和寻找邪恶段错误的探索

Question

下面将是我的代码，然后是 Valgrind 的 txt。我不知道为什么它这么长，非常抱歉。我真的很新。请帮助我理解为什么在编译时没有错误消息但程序失败？我知道这是某个地方的内存泄漏，但我不知所措。我应该在下面的困惑中寻找什么？

#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;
}

样本输入

2
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 乙 99
300 3 C 98
400 4 D 97
500 5 东 96
600 6 华氏度 95

Answer 1

到达这条线时

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

您在队列中有一个指向 currnode 的实时指针.下次您调用队列函数时，它将尊重该指针。需要在 dequeue()中调整队列的内容.