Question

每当我尝试删除一个HashMap的元素时，我在C ++代码中得到一个错误（不是我的代码...... C ++人的代码 - 特别是xmemory0）。我确定错误在我的最后，但我不知道在哪里，因为调试器告诉我它在其他地方。我的HashMap已经过全面测试，除了当我尝试删除HashElement时，它似乎运行正常。我很确定在删除之前没有任何东西指向HashElement（我认为这是第一个猜测）。当我尝试删除HashElement时，有人可以告诉我为什么会收到错误吗？这是我的堆栈跟踪：

    msvcr120d.dll!operator delete(void *)   Unknown
>   MyProgram.exe!std::allocator<char>::deallocate(char * _Ptr, unsigned int __formal) Line 573 C++
    MyProgram.exe!std::_Wrap_alloc<std::allocator<char> >::deallocate(char * _Ptr, unsigned int _Count) Line 859    C++
    MyProgram.exe!std::basic_string<char,std::char_traits<char>,std::allocator<char> >::_Tidy(bool _Built, unsigned int _Newsize) Line 2284 C++
    MyProgram.exe!std::basic_string<char,std::char_traits<char>,std::allocator<char> >::~basic_string<char,std::char_traits<char>,std::allocator<char> >() Line 992 C++
    MyProgram.exe!HashElement::~HashElement() Line 12   C++

以下是代码：

HashElement.h

#pragma once

#include <string>

class HashElement
{
private:
    int key_;
    std::string value_;
public:
    HashElement(int, std::string);
    ~HashElement();
    HashElement *next_element_;
    int GetKey();
    std::string GetValue();
};

HashElement.cpp

#include "HashElement.h"

HashElement::HashElement(int key, std::string value)
{
    key_ = key;
    value_ = value;
    next_element_ = nullptr;
}

HashElement::~HashElement()
{
}  //This is the last line before it goes off into not my code

int HashElement::GetKey(){
    return key_;
}

std::string HashElement::GetValue(){
    return value_;
}

我也很乐意发布HashMap本身，但我不认为错误与实际的HashMap代码有关，所以我暂时不讨论它以使这篇文章更具可读性。

编辑：

刚刚发现该bug确实存在于我的HashMap中。不知道在哪里。我在想这个，因为简单地创建和删除HashElement并没有重现错误。但这是代码：

HashMap.h

#pragma once
#include <string>

#include "HashElement.h"

class HashMap
{
private:
    HashElement **map_;
    int size_;
    int count_;
public:
    HashMap(int);
    ~HashMap();
    int GetHash(int);
    void Put(int, std::string);
    std::string GetElement(int);
    bool Contains(int);
    void Remove(int);
    int GetCount();
};

HashMap.cpp

#include "HashMap.h"

HashMap::HashMap(int size)
{
    size_ = size;
    map_ = new HashElement*[size_]();
}

HashMap::~HashMap()
{
    for (int i = 0; i < size_; i++){
        int hash = GetHash(i);
        if (!map_[hash]){
            continue;
        }
        HashElement *currentElement = map_[hash];
        HashElement *nextElement = map_[hash];
        while (nextElement->next_element_){
            nextElement = nextElement->next_element_;
            delete currentElement;
            currentElement = nextElement;
        }
        delete currentElement;
    }
}

int HashMap::GetHash(int key){
    return key % size_;
}

void HashMap::Put(int key, std::string value){
    int hash = GetHash(key);
    if (!map_[hash]){
        map_[hash] = new HashElement(key, value);
    }
    else{
        HashElement *lastElement = map_[hash];
        while (lastElement->next_element_){
            lastElement = lastElement->next_element_;
        }
        lastElement->next_element_ = new HashElement(key, value);
    }
    count_++;
}

std::string HashMap::GetElement(int key){
    int hash = GetHash(key);
    if (map_[hash]){
        HashElement *currentElement = map_[hash];
        while (currentElement->GetKey() != key && currentElement->next_element_){
            currentElement = currentElement->next_element_;
        }
        return currentElement->GetValue();
    }
    return nullptr;
}

bool HashMap::Contains(int key){
    int hash = GetHash(key);
    if (map_[hash]){
        HashElement *currentElement = map_[hash];
        while (currentElement->GetKey() != key && currentElement->next_element_){
            currentElement = currentElement->next_element_;
        }
        if (currentElement->GetKey() == key){
            return true;
        }
    }
    return false;
}

void HashMap::Remove(int key){
    if (!Contains(key)){
        return;
    }
    int hash = GetHash(key);
    HashElement *currentElement = map_[hash];
    if (!currentElement->GetKey() == key){
        HashElement *previousElement = currentElement;
        currentElement = currentElement->next_element_;
        while (currentElement->GetKey() != key){
            previousElement = currentElement;
            currentElement = currentElement->next_element_;
        }
        if (currentElement->next_element_){
            previousElement->next_element_ = currentElement->next_element_;
        }
    }
    delete currentElement;
    count_--;
}

int HashMap::GetCount(){
    return count_;
}

Answer 1

我收到了外界帮助，然后在@leewangzhong的评论中给予了帮助。问题出在Remove() HashMap.cpp方法中。我确实有一个悬垂的指针。以下是更正后的方法：

void HashMap::Remove(int key){
    if (!Contains(key)){
        return;
    }
    int hash = GetHash(key);
    HashElement *currentElement = map_[hash];
    if (currentElement->GetKey() == key){
        delete currentElement;
        map_[hash] = nullptr;
    }
    else{
        HashElement *previousElement = currentElement;
        currentElement = currentElement->next_element_;
        while (currentElement->GetKey() != key){
            previousElement = currentElement;
            currentElement = currentElement->next_element_;
        }
        previousElement->next_element_ = currentElement->next_element_;
        delete currentElement;
    }
    count_--;
}

在xmemory0中删除HashMap元素时出错

1 个答案: