分段错误：C++ 代码中的 11 和 malloc 错误

Question

好的，所以我知道这段代码中可能有很多错误。我对动态内存分配、指针等很陌生。

头文件account.h是我们教授给我们的。我们被告知不要对 .h 文件进行任何更改。

实现文件是我写的。主要功能仅用于基本的初始测试。我们得到了另一个文件来实际测试帐户类的实现。

如果我不注释掉 cout 名称行，我会收到 seg fault 11 错误。 如果我这样做，它会打印帐号，但会抛出此错误：

Test(29976) malloc: * 对象 0x62c1aa18c9d8374 的错误：未分配被释放的指针* 在 malloc_error_break 中设置断点以进行调试
中止陷阱：6

任何帮助都将不胜感激！

这是头文件：

class account
{
public:
    typedef char* string;
    static const size_t MAX_NAME_SIZE = 15;
    // CONSTRUCTOR
    account (char* i_name, size_t i_acnum, size_t i_hsize);
    account (const account& ac);
    // DESTRUCTOR
    ~account ( );
    // MODIFICATION MEMBER FUNCTIONS
    void set_name(char* new_name);
    void set_account_number(size_t new_acnum);
    void set_balance(double new_balance);
    void add_history(char* new_history);
    // CONSTANT MEMBER FUNCTIONS
    char* get_name ( ) const;
    size_t get_account_number ( ) const;
    double get_balance( ) const;
    size_t get_max_history_size( ) const;
    size_t get_current_history_size ( ) const;
    string* get_history( ) const;
    friend ostream& operator <<(ostream& outs, const account& target);
private:
    char name[MAX_NAME_SIZE+1]; //name of the account holder
    size_t ac_number; //account number
    double balance; //current account balance
    string *history; //Array to store history of transactions
    size_t history_size; //Maximum size of transaction history
    size_t history_count; //Current size of transaction history
};

这里是实现文件：

// File: account.cxx
// Author: Mike Travis
// Last Modified: Mar 3, 2012
// Description: implementation of Account class as prescribed by the file account.h

#include <cstdlib>
#include <stdio.h>
#include <iostream>
#include "account.h"

using namespace std;

//Constructor

account::account(char* i_name, size_t i_acnum, size_t i_hsize){
    string *d_history;
    d_history = new string[i_hsize];

    for(int i = 0; i<i_hsize; i++){
        name[i] = i_name[i];
    }
    ac_number = i_acnum;
    history_size = i_hsize;
    history_count = 0; 
}


account::account(const account& ac){
    string *d_history;
    d_history = new string[ac.history_size];

    for( int i=0; i<ac.get_current_history_size(); i++){
        strcpy(d_history[i], history[i]);
    }

    strcpy(name,ac.get_name());
    ac_number = ac.get_account_number();
    history_size = ac.get_max_history_size();
    history_count = ac.get_current_history_size();
}

account::~account(){    delete [] history;  }

void account::set_name(char* new_name){                 strcpy(name, new_name); }
void account::set_account_number(size_t new_acnum){     ac_number = new_acnum;  }
void account::set_balance(double new_balance){          balance = new_balance;  }
void account::add_history(char* new_history){
    strcpy(history[history_count], new_history);
    history_count++;
}

char* account::get_name() const {
    char* name_cpy;
    strcpy(name_cpy, name);
    return name_cpy;
}

size_t account::get_account_number() const{             return ac_number;       }
double account::get_balance() const{                    return balance;         }
size_t account::get_max_history_size() const{           return history_size;    }
size_t account::get_current_history_size() const{       return history_count;   }
//string* account::get_history() const{                         return *history;        }


int main(){

    account test1("mike travis", 12345, 20);
    //cout<<"\nname: "<< test1.get_name();

    cout<<"\n\nacnum: "<<test1.get_account_number()<<"\n\n";

    return 0;
}

Answer 1

在account 的析构函数中，删除history 数组。但是，在构造函数中，您分配（并泄漏）了一个存储在局部变量d_history 中的数组。您大概想将其分配给成员变量 history - 因为您没有，如果您到达析构函数，它会给您一个错误，说您正在释放 history 但从未分配过它。

复制构造函数中也有类似的错误。

您的代码中还有其他错误，我假设您会在执行过程中发现这些错误 - 例如，get_name() 将无法正常工作。我怀疑头文件在这里没有帮助，但如果你不应该改变它，那就没什么可做的了。

Answer 2

我已经为您编写了一些代码并纠正了史诗般的错误（即使是在头文件中，抱歉 ;)）。它仍然非常丑陋和 c-ish，但也许你可以通过阅读它学到一些东西：

#include <cstddef>
#include <ostream>

class account
{
    // The whole class makes no sense, since it has no useful
    // member function or anything like this.
    // Furthermore, the class provides almost full access to all its member variables.
    // At this point one could just make everything public.

    // This is not even exception safe when the constructor throws.
    // A good implementation would use history_entry and history classes, 
    // together with std::string and std::vector/std::deque
    // And it would provide some sort of functionality. ;)

public:
  account(const char* name, unsigned number, std::size_t history_max_size);
  account(const account& other);
  ~account();

    const char* name() const;
  unsigned number() const;
  double balance() const;
    const char* const* history() const;
    std::size_t history_size() const;
  unsigned history_max_size() const;

  void set_name(const char* new_name);
  void set_number(unsigned new_number);
  void set_balance(double new_balance);
  void add_history(const char* new_history);

private:
  char* name_;
  unsigned number_;
  double balance_;
  char** history_;
    std::size_t history_size_;
    const std::size_t history_max_size_;
};

std::ostream& operator << (std::ostream& stream, const account& a);


#include <cassert>
#include <cstring>

account::account(const char* name, unsigned number, std::size_t history_max_size)
    : name_(0)
    , number_(number)
    , balance_(0.0)
    , history_(new char*[history_max_size])
    , history_size_(0)
    , history_max_size_(history_max_size)
{
    assert(name != 0);
    assert(history_max_size != 0);
    set_name(name);
}

account::account(const account& other)
    : name_(0)
    , number_(other.number_)
    , balance_(other.balance_)
    , history_(new char*[other.history_max_size_])
    , history_size_(other.history_size_)
    , history_max_size_(other.history_max_size_)
{
    set_name(other.name_);
    for (std::size_t i = 0; i != other.history_size_; ++i)
    {
        history_[i] = new char[std::strlen(other.history_[i]) + 1];
        strcpy(history_[i], other.history_[i]);
    }
}

account::~account()
{
    delete[] name_;

    for (std::size_t i = 0; i != history_size_; ++i)
        delete[] history_[i];
    delete[] history_;
}

const char* account::name() const
{
    return name_;
}

unsigned account::number() const
{
    return number_;
}

double account::balance() const
{
    return balance_;
}

const char* const* account::history() const
{
    return history_;
}

std::size_t account::history_size() const
{
    return history_size_;
}

unsigned account::history_max_size() const
{
    return history_max_size_;
}

void account::set_name(const char* new_name)
{
    if (name_)
        delete[] name_;

    name_ = new char[std::strlen(new_name) + 1];
    std::strcpy(name_, new_name);
}

void account::set_number(unsigned new_number)
{
    number_ = new_number;
}

void account::set_balance(double new_balance)
{
    balance_ = new_balance;
}

void account::add_history(const char* new_history)
{
    if (history_size_ == history_max_size_)
    {
        delete[] history_[0]; // delete oldest entry
        for (std::size_t i = 0; i != history_size_ - 1; ++i)
            history_[i] = history_[i + 1];
        --history_size_;
    }

    history_[history_size_] = new char[strlen(new_history) + 1];
    std::strcpy(history_[history_size_], new_history);
    ++history_size_;
}

std::ostream& operator << (std::ostream& stream, const account& a)
{
    return stream << "account [name: " << a.name() << ", number: " 
        << a.number() << ", balance: " << a.balance() << ']';
}


#include <iostream>

int main()
{
    account a("Hello!", 500, 5);
    a.set_balance(12.546);
    for (int i = 50; i--; )
        a.add_history("Yaaay..");
    //account b = a;
    std::cout << a << '\n';
}