c++ - valgrind 在单链接列表示例中显示内存泄漏

Question

Here is my code.

#include <bits/stdc++.h> 
using namespace std; 

class Node { 
public: 
    int data; 
    Node* next; 
}; 

void printList(Node* n) 
{ 
    while (n != NULL) { 
        cout << n->data << " "; 
        n = n->next; 
    } 
} 

void delete_list(Node *n)
{
    Node *tmp = NULL;
    tmp = new Node();
    while (n != NULL){
        tmp=n->next;
        delete (Node *)n;
        n=tmp;
    }
    delete (Node *)tmp;
}


int main() 
{ 
    Node* head = NULL; 
    Node* second = NULL; 
    Node* third = NULL; 

    head = new Node(); 
    second = new Node(); 
    third = new Node(); 

    head->data = 1; 
    head->next = second;

    second->data = 2;
    second->next = third; 

    third->data = 3;
    third->next = NULL; 

    printList(head); 

    // Delete the entire list
    delete_list(head);

    return 0; 
} 

• 堆摘要:在此处输入代码 在导出处使用:1 个 block 中的 16 个字节 堆总使用量:6 次分配，5 次释放，分配了 73,792 字节 1个 block 中的16个字节肯定丢失在丢失记录1 of 1中 在 0x4C3017F:operator new(unsigned long)(在/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so 中) 通过 0x10895E: delete_list(Node*) (demo.cpp:24) 通过 0x108A87: main (demo.cpp:58) 泄漏总结: 绝对丢失:1 个 block 中的 16 个字节 间接丢失:0 个 block 中的 0 个字节 可能丢失:0 个 block 中的 0 个字节 仍然可达:0 个 block 中的 0 个字节 抑制:0 个 block 中的 0 个字节 对于检测到的和抑制的错误的计数，重新运行:-v 错误摘要:1 个上下文中的 1 个错误(抑制:0 个中的 0 个)

Answer 1

void delete_list(Node *n)
{
    Node *tmp = NULL;

    // this is your memory leak:
    // you just created a new node ...
    tmp = new Node();

    while (n != NULL)
    {
        // ... and very first thing you do is assigning another node to the only
        // pointer holding the node created just before
        tmp = n->next;

        delete (Node *)n;
        n = tmp;
    }

    // apart from cast being obsolete (tmp HAS appropriate type!)
    // tmp is already nullptr and you don't delete anything at all
    delete (Node *)tmp;
}

这个例子很好地展示了为什么尽可能保持局部变量是个好主意:

while (n != NULL)
{
    Node* tmp = n->next;
    delete (Node *)n;
    n = tmp;
}

你根本无法在不需要的情况下分配任何东西(甚至创建不相关的对象)或试图删除不再存在的东西......