C++在while循环后加一行代码报错

Question

我已尽力寻找能够解决我的具体问题的答案，但不幸的是，我找不到满足我需求的答案。

我正在用 c++ 为我编写的语言编写汇编程序。编写汇编程序涉及两个 classes，它们一直在导致问题，这些问题确实很难调试。我的调试技术已经转移到添加和删除输出流命令，如

std::cout << "TEST";

这最终会破坏或修复程序。我使用的 IDE 是 Xcode.

我正在处理的两个 class 是一个 LinkedList class 和一个 SymbolTable class，我将它们用作符号解析的散列 table .

LinkedList.h

#include <iostream>
using namespace std;

struct Node{
    string data;
    int address;
    Node* next = nullptr;
};

class LinkedList{
private:
    Node* main_ptr;
    int length;
public:
    LinkedList();

    void insertNode(string, int);
    void deleteNode(string);
    void displayList();

    bool contains(string, int* = nullptr);
    int getLength();

    ~LinkedList();
};

LinkedList.cpp

#include "LinkedList.h"

LinkedList::LinkedList(){
    main_ptr = nullptr;
    length = 0;
}

void LinkedList::insertNode(string data, int address){
    Node* newNode = new Node;
    newNode->data = data;
    newNode->address = address;

    if (!main_ptr){
        main_ptr = newNode;
    } else {
        newNode->next = main_ptr;
        main_ptr = newNode;
    }
    length++;
}

void LinkedList::deleteNode(string data){
    if (main_ptr){
        int current_length = length;
        if (main_ptr->data == data){
            main_ptr = main_ptr->next;
            return;
        }
        Node* q = main_ptr;
        Node* p = q;
        q = q->next;
        while (q){
            if (q->data == data){
                p->next = q->next;
                length--;
                return;
            }
            p = q;
            q = q->next;
        }
        if (current_length == length) cout << "Node was not found" << endl;
    } else {
        cout << "List is empty, cannot delete node!" << endl;
    }
}

void LinkedList::displayList(){
    if (!main_ptr){
        cout << "List is empty!\n";
    } else {
        Node* temp = main_ptr;
        while (temp){
            cout << temp->data;
            temp = temp->next;
        }
        cout << endl;
    }
}

bool LinkedList::contains(string data, int* address){
    if (main_ptr == nullptr) return false;
    else {
        Node* temp = main_ptr;
        while(temp != nullptr){
            if (temp->data == data) {
                address = &(temp->address);
                return true;
            }
            temp = temp->next;
        }
        return false;
    }
}

int LinkedList::getLength(){
    return length;
}

LinkedList::~LinkedList(){
    if (main_ptr){
        Node* q = main_ptr;
        Node* p = q;
        while (q){
            q = q->next;
            delete p;
            p = q;
        }
    }
}

SymbolTable.h

#include "LinkedList.h"
#include <iostream>

class SymbolTable{
private:
    LinkedList table[701];
public:
    SymbolTable();

    void addEntry(string, int);
    void printTable();
    bool contains(string, int*);

    int convertName(string);
};

SymbolTable.cpp

#include "SymbolTable.h"

SymbolTable::SymbolTable(){
}

void SymbolTable::addEntry(string name, int memory){
    int address = convertName(name);
    table[address].insertNode(name, memory);
}

void SymbolTable::printTable(){
    for (int i = 0; i < 701; i++)
        table[i].displayList();
}

bool SymbolTable::contains(string name, int* memory){
    return table[convertName(name)].contains(name, memory);
}

int SymbolTable::convertName(string name){
    int aggregate = 1;
    const char* c_name = name.c_str();
    for (int i = 0; i < name.length(); i++){
        aggregate *= (int)c_name[i];
    }
    return aggregate%701;
}

现在是我的实际问题。以下是主要功能：

#include "Parser.h"
#include "SymbolTable.h"

using namespace std;

int main(int argc, const char * argv[]) {

    ifstream inputFile;
    ofstream outputFile;

    inputFile.open("/Users/Azaldin/Desktop/nand2tetris/projects/06/max/Max.asm");
    outputFile.open("/Users/Azaldin/Desktop/nand2tetris/projects/06/max/Max.hack");

    Parser a(inputFile);
    SymbolTable s;

    int commandType = -1;
    string command;
    int a_position = 16;
    int currentLine = 0;

    while (a.hasMoreCommands()){
        a.advance();
        commandType = a.commandType();
        command = a.symbol();

        if (commandType == 0){
            if (!s.contains(command, nullptr)){
                s.addEntry(command, a_position);
                a_position++;
            }
        }

        if (commandType == 2){
            //cout << command << endl;
            if (!s.contains(command, nullptr)){
                s.addEntry(command, currentLine);
                //cout << command << endl;
            }
        }

        currentLine++;
    }

    string x;  //<<<<<<<<<< ADDING THIS LINE BREAKS THE PROGRAM
    cout << "Hi";

    inputFile.close();
    outputFile.close();

    return 0;
}

在主函数中添加上面指向的行后，程序中断。经调试，主线程出现如下问题：

Thread 1:EXC_BAD_ACCESS (code = 1, address=0x25fbfef80)

导致此问题的命令链：

if (!s.contains(command, nullptr)){ 来自主函数
return table[convertName(name)].contains(name, memory); 来自 SymbolTable.cpp "contains" 函数
if (temp->data == data) { 来自 LinkedList.cpp "contains" 函数

链命令的其余部分指向字符串 class == 运算符，然后指向左侧的 .size() 函数。

谢谢！

Answer 1

PaulMcKenzie 的以下评论帮助解决了问题：

Also, aggregate *= (int)c_name[i]; -- there is no guarantee that this will be a positive number, since a character may be signed, thus giving you values of -1 and below. Thus your return of return aggregate%701; isn't going to return what you expected (a number >= 0).

事实证明，传递给 SymbolTable class 中的 convertName 函数的参数之一导致程序损坏了内存。我添加了一个 if 语句来解决问题。

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