c - 队列 valgrind 错误

Question

此代码似乎有效。但是，我收到此代码的 Valgrind 错误:

#include <stdlib.h>
#include "queue.h"
#include "queuepriv.h"
#include <string.h>

Queue *Queue_init(void)
{
    Queue *q = calloc(1, sizeof(Queue));
    return q;
}

int Queue_enqueue(Queue *q, const char *id, const char *name)
{
    // implement this function
    struct student *new = calloc(1, sizeof(struct student));
    if (strlen(id) <= 6) {
      strcpy(new->id, id);
      new->name = malloc(strlen(name) + 1);
      strcpy(new->name, name);
      new->name[strlen(name)] = '\0';
      if (q->last)
        q->last->next = new;
      q->last = new;
      q->last->next = NULL;

      if (!q->first)
        q->first = q->last;
      return 1;
    } else {
      return 0;
    }

}

char *Queue_firstID(Queue *q)
{
    if (q && q->first)
        return q->first->id;
    else
        return NULL;
}

char *Queue_firstName(Queue *q)
{
    if (q && q->first)
        return q->first->name;
    else
        return NULL;
}

int Queue_dequeue(Queue *q)
{
    // implement this function
    if (q->first) {
      struct student *fst = q->first;
      struct student *nxt = fst->next;
      free(fst->name);
      free(fst);
      q->first = nxt;
      if (!q->first)
        q->last = NULL;
      return 1;
    } else {
      return 0;
    }
}

int Queue_drop(Queue *q, const char *id)
{
    // implement this function
    struct student *current = q->first;
    struct student *previous = NULL;

    while(current) {
      if (!strcmp(id, current->id)) {
        if(current == q->first) {
          q->first = current->next;
        } else if(current == q->last) {
          q->last = previous;
          q->last->next = NULL;
        } else {
          previous->next = current->next;
        }
        free(current->name);
        free(current);
        return 1;
      }
      previous = current;
      current = current->next;
    }
    return 0;
}

void Queue_delete(Queue *q)
{
    if (q) {
        while(Queue_dequeue(q));
        free(q);
    }
}

queuepriv.h:

#ifndef QUEUEPRIV_H
#define QUEUEPRIV_H

#include "queue.h"

/* One student in linked list*/
struct student {
    char id[7];  // student ID: 6 characters + '\0'
    char *name;  // Name of student, allocated dynamically
    struct student *next;  // next student in linked list
};

/* For storing the first and last item in linked list
 * If list is empty, both <first> and <last> are NULL
 * If list has one element, <first> and <last> point to the same place
 */
struct queue {
    struct student *first;
    struct student *last;
};

#endif

Valgrind 输出:

==16237== 24 bytes in 1 blocks are definitely lost in loss record 48 of 61
==16237==    at 0x4C2FB55: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==16237==    by 0x4034F4: Queue_enqueue (queue.c.nomain.c:15)
==16237==    by 0x4021DD: test_Queue_enqueue (test_source.c:104)
==16237==    by 0x407542: srunner_run (in /tmp/user/867402f030a5e9991da6016803cf05863b3e7662e8f00ef3ced1e3ca2e2ded8c/c-kurssi/Module_3/07_queue/test/test)
==16237==    by 0x402E4B: tmc_run_tests (tmc-check.c:122)
==16237==    by 0x402B06: main (test_source.c:226)
==16237== 
==16238== 24 bytes in 1 blocks are definitely lost in loss record 50 of 64
==16238==    at 0x4C2FB55: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==16238==    by 0x4034F4: Queue_enqueue (queue.c.nomain.c:15)
==16238==    by 0x402449: test_Queue_dequeue (test_source.c:135)
==16238==    by 0x407542: srunner_run (in /tmp/user/867402f030a5e9991da6016803cf05863b3e7662e8f00ef3ced1e3ca2e2ded8c/c-kurssi/Module_3/07_queue/test/test)
==16238==    by 0x402E4B: tmc_run_tests (tmc-check.c:122)
==16238==    by 0x402B06: main (test_source.c:226)
==16238== 
==16239== 24 bytes in 1 blocks are definitely lost in loss record 49 of 64
==16239==    at 0x4C2FB55: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==16239==    by 0x4034F4: Queue_enqueue (queue.c.nomain.c:15)
==16239==    by 0x4027C1: test_Queue_drop (test_source.c:182)
==16239==    by 0x407542: srunner_run (in /tmp/user/867402f030a5e9991da6016803cf05863b3e7662e8f00ef3ced1e3ca2e2ded8c/c-kurssi/Module_3/07_queue/test/test)
==16239==    by 0x402E4B: tmc_run_tests (tmc-check.c:122)
==16239==    by 0x402B06: main (test_source.c:226)
==16239== 

我无法弄清楚内存泄漏在哪里，因为我认为我释放了出列和删除函数中的所有内存。

提前谢谢你。

Answer 1

在这段代码中

int Queue_enqueue(Queue *q, const char *id, const char *name)
{
    // implement this function
    struct student *new = calloc(1, sizeof(struct student));
    if (strlen(id) <= 6) {
      strcpy(new->id, id);
      new->name = malloc(strlen(name) + 1);
      strcpy(new->name, name);
      new->name[strlen(name)] = '\0';
      if (q->last)
        q->last->next = new;
      q->last = new;
      q->last->next = NULL;

      if (!q->first)
        q->first = q->last;
      return 1;
    } else {
      return 0;
    }

}

strlen(id) > 6 时内存泄漏。

在这种情况下，您可以:

int Queue_enqueue(Queue *q, const char *id, const char *name)
{
    // implement this function
    struct student *new = calloc(1, sizeof(struct student));
    if (strlen(id) <= 6) {
        //don't get in here
        ....
    } else {
      // get in here and leak the memory assigned to new
      return 0;
    }

}

也许你应该把它改成:

int Queue_enqueue(Queue *q, const char *id, const char *name)
{
    // implement this function
    struct student *new = calloc(1, sizeof(struct student));
    if (strlen(id) <= 6) {
        ....
    } else {
      free(new);   // Free the memory
      return 0;
    }

}