c++ - c++ 中重新定义的 << 运算符的奇数输出

Question

我有一个运行时错误，我这辈子都无法解决。我的程序几乎完成了我想要的，但是有一些损坏的字符打印为乱码。该程序应该接收一个代表森林的文本文件，构建森林，然后遍历森林以将其打印出来。树可以任意大，每个节点可以有任意多个子节点。森林在文本文件中表示如下:

a  
  b  
    c  
  d  
    e  
    z  
f  
  g  
    h  
  i  
    j  

并且将转换为以下两棵树的森林:

    a     
   / \  
  b   d  
 /   / \  
c   e   z  

    f      
   / \  
  g   i  
 /   /  
h   j  

代码中被注释掉的行是我测试时遗留下来的，以确保文件被正确读取并且我创建的节点被正确标记和指向。

我的代码如下:

(文件节点.h)

#ifndef NODE_H
#define NODE_H


template<typename NODETYPE> class Forest;

template<typename NODETYPE> class ForestNode
{
    friend class Forest<NODETYPE>;

    public:
        ForestNode();

        NODETYPE getTag() const;
        ForestNode<NODETYPE> * getLeftChild() const;
        ForestNode<NODETYPE> * getSibling() const;
        void setTag(NODETYPE);
        void setLeftChild(ForestNode<NODETYPE>*);
        void setSibling(ForestNode<NODETYPE>*);
    private:
        NODETYPE tag;
        ForestNode<NODETYPE> * leftChild;
        ForestNode<NODETYPE> * sibling;
};

template<typename NODETYPE> ForestNode<NODETYPE>::ForestNode()
    : tag(0), leftChild(NULL), sibling(NULL)
{

}

template<typename NODETYPE> NODETYPE ForestNode<NODETYPE>::getTag() const
{
    return tag;
}

template<typename NODETYPE> ForestNode<NODETYPE>* ForestNode<NODETYPE>::getLeftChild() const
{
    return leftChild;
}

template<typename NODETYPE> ForestNode<NODETYPE>* ForestNode<NODETYPE>::getSibling() const
{
    return sibling;
}

template<typename NODETYPE> void ForestNode<NODETYPE>::setTag(NODETYPE info)
{
    this->tag = info;
}
template<typename NODETYPE> void ForestNode<NODETYPE>::setLeftChild(ForestNode<NODETYPE>* info)
{
    leftChild = info;
}
template<typename NODETYPE> void ForestNode<NODETYPE>::setSibling(ForestNode<NODETYPE>* info)
{
    sibling = info;
}


#endif // NODE_H

(文件forest.h)

#ifndef FOREST_H
#define FOREST_H

#include <iostream>
#include <cstdlib>
#include <string>
#include "node.h"

using namespace std;

template<typename NODETYPE> class Forest
{


    template<NODETYPE> friend ostream& operator<<(ostream& output, const Forest<NODETYPE>& f1);

    template<NODETYPE> friend void outputHelper(ostream& output, const ForestNode<NODETYPE>& currentNode, int depth);

    friend void inputHelper(istream& file, int previousDepth, ForestNode<char*>& previousNode, ForestNode<char*>* *nodeArray, int& nodeCount);

    friend istream& operator>>(istream& file, Forest<char*>& f1);

    public:

        Forest();
        Forest( const Forest& otherForest);
        void nodes(int&) const;

        ForestNode<NODETYPE> * root;

};

template<typename NODETYPE>ostream& operator<<(ostream& output, const Forest<NODETYPE>& f1)
{
    int depth = 0;

    output << f1.root->getTag();
    outputHelper(output, f1.root, depth);

    return output;
}

void outputHelper(ostream& output, const ForestNode<char*> *currentNode, int depth)
{
    for(int i = 0; i < depth; i++)
    {
        output << ' ' << ' ';
    }

    output << currentNode->getTag();
    output << endl;

    if(currentNode->getLeftChild() != NULL)
    {
        outputHelper(output, currentNode->getLeftChild(), depth+1);
    }

    if(currentNode->getSibling() != NULL)
    {
        outputHelper(output, currentNode->getSibling(), depth);
    }

}


void inputHelper(istream& file, int previousDepth, ForestNode<char*>* previousNode, ForestNode<char*> ** nodeArray, int& nodeCount)
{
    int spaceCounter = 0;

    while(file.peek() == ' ')
    {
        spaceCounter++;
        file.ignore(1);
    }


    ForestNode<char*>* currentNode = new ForestNode<char*>();

    char bar[100];
    file.getline(bar, 100);
//        cout << bar << endl;

    currentNode->setTag(bar);
//        cout << currentNode->getTag();

    if(spaceCounter/2 < previousDepth)
    {
        for(int i = (spaceCounter/2)+1; i < nodeCount; i++)
        {
            nodeArray[i] = NULL;
        }
    }

    cout << "array:";


    for(int i = 0; i < spaceCounter/2; i++)
    {
        cout << nodeArray[i]->getTag();
    }

//        cout << endl;

//        cout << spaceCounter/2 << ':';

    if(spaceCounter/2 == previousDepth+1)
    {
        previousNode->setLeftChild(currentNode);
//      cout << "i'm a child:" << previousNode->getLeftChild()->getTag() << " and my parent is:" << nodeArray[(spaceCounter/2)-1]->getTag();
        nodeArray[spaceCounter/2] = currentNode;
    }
    else
    {
        if(!(nodeArray[spaceCounter/2] == NULL))
        {
        nodeArray[spaceCounter/2]->setSibling(currentNode);
//      cout << "I'm a sibling:" << nodeArray[spaceCounter/2]->getSibling()->getTag() << " and my older sibling is:" << nodeArray[spaceCounter/2]->getTag();
        nodeArray[spaceCounter/2] = currentNode;
        }

    }

//        cout << endl;

//        cout << currentNode->getTag();

    if(!file.eof())
    {
    inputHelper(file, spaceCounter/2, currentNode, nodeArray, nodeCount);
    }


}

istream& operator>>(istream& file, Forest<char*>& f1)
{
    int charCount = 0;
    int nodeCount = 0;

    file.seekg(0, ios_base::end);

    charCount = file.tellg();

    file.seekg(0, ios_base::beg);

    for(int i=0; i <= charCount; i++)
    {
//            cout << i << ':' << file.peek() << endl;
        if(file.peek() == '\n')
        {
            nodeCount++;
        }
        file.seekg(i);
    }

    file.seekg(0, ios_base::beg);

    nodeCount = nodeCount/2;
    nodeCount = nodeCount + 1;

    ForestNode<char*>* forestNodeArray[nodeCount];//holds pointers to last node of depth i

    char bar[100];
    file.getline(bar, 100);
    cout << bar << endl;

    ForestNode<char*>* foo = new ForestNode<char*>();
    f1.root = foo;
    f1.root->setTag(bar);

    forestNodeArray[0] = f1.root;
    inputHelper(file, 0, f1.root, forestNodeArray, nodeCount);

    return file;
}

结束

(文件 main.h)

#include <iostream>
#include <fstream>
#include "forest.h"

using namespace std;

int main()
{
    Forest<char*> forest;
    filebuf fb;
    fb.open ("forest1.txt",ios::in);
    istream is(&fb);

    is >> forest;

    fb.close();

    cout << forest;
}

我正在使用以下文本文件:

a
  z
    c
      d
    e
      f
  g
    h
  i
    y
x
  w
    m
      n
    o
      p
  q
    r
  s
    t

我的输出如下:

└@GƒtF
  ░≥9
    c
      d
    e
      f
  g
    h
  i
    Eⁿ(
☺
  L⌡(
    m
      n
    o
      p
  q
    r
  s
    t

进程返回 0 (0x0) 执行时间:0.092 秒按任意键继续。

如您所见，输出非常接近应有的结果，但是 ForestNodes 中包含的某些字符或标签已损坏，我终究无法弄清楚原因。任何帮助将不胜感激，我将把你视为人中之神。

Answer 1

据我所知，您的节点包含指向函数 inputHelper() 中的本地缓冲区 bar 的指针。当您在调用 setTag() 后立即打印 getTag() 的结果(注释掉)时，缓冲区仍然有效。但是，一旦函数返回，您的代码就会导致未定义的行为，因为您指的是堆栈中不再有效的某个位置。

您是否考虑过使用 std::string 而不是 char 缓冲区和 char*？ std::string 的自动内存管理和复制语义将解决您的问题。

编辑:输出乱码的原因是较低的堆栈帧被其他一些函数调用覆盖了。树中的 Deper 节点恰好是指距离较远且不太可能被覆盖的内存，这就是为什么它们的值可以正确输出的原因。