Question

处理一个简单的基于C ++指针的堆栈程序。我试图打印一个字符串，它是NameItem类的一部分，PointerStack类将其用作项类型（请参阅代码）。每当我尝试在程序的main（）函数中打印字符串时，控制台会反复打印乱码和嘟嘟声。但是，当我调用PrintPointerStack函数时，没有错误，所有内容都按预期打印。

我试过更改类，重新排列代码，虽然我可以确定哪一行产生错误但我无法弄清楚原因。我完全迷失在这里，之前从未见过这样的事情，所以如果答案很简单并且在谷歌搜索中找到，我很抱歉，但我已经去了几个小时，只是不知道该搜索什么。< / p>

代码如下：

#include <iostream>
#include <string>
#include <stack>
#include <cstddef>
#include <new>
using namespace std;

#include "NameItem.cpp"
#include "Stack.cpp"
#include "PointerStack.cpp"

void PrintPointerStack(PointerStack printer){
    NameItem temp;
    while(!printer.IsEmpty()){
        temp = printer.Top();
        printer.Pop();
        temp.Print();
    }
    cout << endl;
}

int main(){

    string initNames[] = {"Michael","Charlie","Susan","Alexa",
                          "Jason","Candice","Beatrice","Lois",
                          "Peter","Matthew"};
    int initNamesLen = 10;

    PointerStack PStacker, tempPStacker;

    NameItem filler;

    for(int i = 0; i < initNamesLen; i++){
        filler.Init(initNames[i]);
        PStacker.Push(filler);
    }
    cout << endl << "---------- Pointer-based Stack ----------" << endl << endl;

    PrintPointerStack(PStacker);

    cout << "Top: ";
    (PStacker.Top()).Print(); //This is where the program errors. I've tried creating a
                              //temp variable like in the function above, and I've
                              //tried accessing the string directly and printing it
                              //from main() using cout, which produce the same results.
                              //So the error is caused specifically by the cout <<
                              //string statement, when I try to use that statement
                              //within the bounds of the main function.  
    cout << endl;

    PrintPointerStack(PStacker);

    cout << endl << "Popped: ";
    (PStacker.Top()).Print();
    PStacker.Pop();
    (PStacker.Top()).Print();
    PStacker.Pop();
    cout << endl;

    PrintPointerStack(PStacker);

    cout << endl << "Pushed: Sammy Valerie" << endl;
    filler.Init("Sammy");
    PStacker.Push(filler);
    filler.Init("Valerie");
    PStacker.Push(filler);

    PrintPointerStack(PStacker);

    try{
        PStacker.Push(filler);
    }
    catch(FullStack){
        cout << endl << "Stack is full, name not pushed" << endl;
    }

    cout << endl << "Popped: ";
    while(!PStacker.IsEmpty()){
        filler = PStacker.Top();
        PStacker.Pop();
        filler.Print();
    }
    try{
        PStacker.Pop();
    }
    catch(EmptyStack){
        cout << endl << "Stack is empty, name not popped" << endl;
    }

    return 0;
}

PointerStack类

#include "PointerStack.h"

PointerStack::PointerStack(){
    top = NULL;
}

/*PointerStack::~PointerStack(){
    Node* temp;

    while(top != NULL){
        temp = top;
        top = top->next;
        delete temp;
    }
}*/

void PointerStack::Push(NameItem item){
    if(IsFull())
        throw FullStack();
    else{
        Node* location;
        location = new Node;
        location->data = item;
        location->next = top;
        top = location;
    }
}

void PointerStack::Pop(){
    if(IsEmpty())
        throw EmptyStack();
    else{
        Node* temp;
        temp = top;
        top = top->next;
        delete temp;
    }
}

NameItem PointerStack::Top(){
    if(IsEmpty())
        throw EmptyStack();
    else{
        return top->data;
    }
}

bool PointerStack::IsEmpty() const{
    return (top == NULL);
}

bool PointerStack::IsFull() const{
    Node* location;
    try{
        location = new Node;
        delete location;
        return false;
    }
    catch(std::bad_alloc& exception){
        return true;
    }
}

NameItem类

#include <fstream>
#include "NameItem.h"

NameItem::NameItem()
{
    name = " ";
}
RelationType NameItem::ComparedTo(NameItem otherItem) const
{
    if (name < otherItem.name)
        return LESS;
    else if (name > otherItem.name)
        return GREATER;
    else 
        return EQUAL;
}
void NameItem::Init(string value)
{
    name = value;
}
void NameItem::Print() const
{
    cout << name << " ";
}

最后请注意，主程序有更多代码用于测试程序中包含的Stack类。我删除了代码，因为它与错误无关，程序仍然崩溃，但它会立即崩溃，出现一个Windows错误框，而不是控制台乱码/嘟嘟声。不确定这是否相关......

Answer 1

问题是双重的。

首先，您要清空PStacker中的PrintPointerStack()对象，然后尝试访问该空堆栈的顶部元素。这应该抛出EmptyStack。没有发生这种情况的事实也表明了另一个问题（见下文）。

其次，打印giberish（有时）的事实表明您试图通过无效的对象/指针访问数据。实际上，因为您通过pass-by-value传递PrintPointerStack()的参数，所以调用默认的复制构造函数，盲目地复制top指针的值。然后继续删除对象，但原始top中的PStacker指针未更改，因此现在无效。因此你的问题。

要修复，您需要通过指针/引用将参数传递给PrintPointerStack()，或者提供一个更好的适合复制构造函数来执行深层复制（而不是默认复制构造函数提供的浅复制）

运行时错误打印字符串，即使它在函数中工作正常

1 个答案: