Question

我正在用C ++编写程序并遇到了最奇怪的错误。我的程序在main返回0之前崩溃。

我不明白程序在完成之后和返回零之前是如何崩溃的。

这怎么可能？

主要内容如下：

#include <iostream>
#include <iomanip>
#include <utility>
#include <ctime>
#include "Text.h"
#define TIME(start, end) double((end) - (start)) / CLOCKS_PER_SEC


int main(int argc, char* argv[]) {
    argv[1] = "gutenberg_shakespeare.txt";
    argc = 2;

    if (argc == 1) {
        std::cerr << argv[0] << ": missing file operand\n";
        return 1;
    }
    else if (argc != 2) {
        std::cerr << argv[0] << ": too many arguments\n";
        return 2;
    }

    std::clock_t cs, ce;
    std::cout << std::fixed << std::setprecision(3);

    cs = std::clock();
    w3::Text a;
    ce = std::clock();
    std::cout << "Constructor      " << TIME(cs, ce) << " seconds";
    std::cout << " - a.size = " << a.size() << std::endl;

    cs = std::clock();
    w3::Text b(argv[1]);
    ce = std::clock();
    std::cout << "Constructor      " << TIME(cs, ce) << " seconds";
    std::cout << " - b.size = " << b.size() << std::endl;

    cs = std::clock();
    a = b;
    ce = std::clock();
    std::cout << "Copy Assignment  " << TIME(cs, ce) << " seconds";
    std::cout << " - a.size = " << a.size() << std::endl;

    cs = std::clock();
    a = std::move(b);
    ce = std::clock();
    std::cout << "Move Assignment  " << TIME(cs, ce) << " seconds";
    std::cout << " - a.size = " << a.size() << std::endl;

    cs = std::clock();
    w3::Text c = a;
    ce = std::clock();
    std::cout << "Copy Constructor " << TIME(cs, ce) << " seconds";
    std::cout << " - c.size = " << c.size() << std::endl;

    cs = std::clock();
    w3::Text d = std::move(a);
    ce = std::clock();
    std::cout << "Move Constructor " << TIME(cs, ce) << " seconds";
    std::cout << " - d.size = " << d.size() << std::endl;

    cs = std::clock();
    ce = std::clock();
    std::cout << "Destructor       " << TIME(cs, ce) << " seconds\n";

    std::cout << "DONE";
    return 0;
}

文本cpp文件：

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

using namespace w3;

Text::Text() {

}

//MOVE Copy constructor
Text::Text(Text&& movefrom){
    std::cout << "MOE COPY CONSTRUCTOR" << std::endl;
    filename = movefrom.filename;
    entries  = movefrom.entries;
    data     = movefrom.data;

    movefrom.entries = 0;
    movefrom.data    = nullptr;
}

//move assig operator
Text&& Text::operator=(Text&& movefrom) {
    std::cout << "move assig operator" << std::endl;

    if (&movefrom != this) {
        filename = movefrom.filename;
        entries  = movefrom.entries;

        if (data != nullptr) {
            delete[] data;
            entries = 0;
        }

        movefrom.data = nullptr;
    }

    movefrom.entries = 0;
    return std::move(*this);
}

//constructor
Text::Text(const std::string& mystring) {
    std::cout << "Constructor" << std::endl;
    int count = 0;
    filename = mystring;

    std::string buffer;
    std::ifstream myfile(filename);

    if (!myfile.is_open()) {
        filename.clear();
    }

    if(myfile.is_open()) {

        while (getline(myfile, buffer)) { //Will fail at end of file
            //std::cout << buffer << std::endl;
            count++;
        }
        std::cout << "File is read";

        data = new std::string[count];

        myfile.clear();//.................reset file state
        myfile.seekg(0, myfile.beg);//....reset file position

        int x = 0;
        for (int i = 0; i < count; i++) {
            getline(myfile, data[i]);

        }

        std::cout << std::endl << "File is copied" << std::endl;

        entries = count;
        myfile.close();
    }   
}

//default constructor
Text::~Text() {
    if (data != nullptr) {
        delete[] data;
        entries = 0;
    }
    data = nullptr;
}

//copy constructor
Text::Text(const Text& copyfrom) {
    data  = nullptr;  //The object is empty
    *this = copyfrom;
}

const Text& Text::operator=(const Text& copyfrom) {
    std::cout << "copy assign operator" << std::endl;

    if (this != &copyfrom) {

        if (data != nullptr) {
            delete[] data;
            entries = 0;
        }
        filename = copyfrom.filename;
        entries = copyfrom.entries;
        if (copyfrom.data != nullptr) {  //If the object is not empty
            data = new std::string[entries];
            for (int i = 0; i < entries; i++) {
                data[i] = copyfrom.data[i];
            }
        }
        std::cout << "Data is assigned" << std::endl;
    }

    return *this;
}


size_t Text::size() const {
    return entries;

}

void Text::print() {

    for (int i = 0; i < entries; i++) {
        std::cout << data[i] << std::endl;
    }

}

编辑＆gt;＆gt;＆gt;头文件

#ifndef TEXT_H
#define TEXT_H


#define FILE_LENGTH 10

#include <string>
#include <iostream>


namespace w3 {

    class Text {

    private:
        std::string filename;
        std::string * data = nullptr;
        size_t entries;

    public:
        Text(Text&& movefrom);
        Text&& operator=(Text&& movefrom);

        Text();
        Text(const std::string& mystring);
        Text(const Text& copyfrom);
        ~Text();

        const Text& operator=(const Text& copyfrom);

        size_t size() const;

        void print();
    };
}

#endif

Answer 1

我不得不说，失败不是我所期待的。对此表示赞赏。我期望双删除，因为两个对象指向同一个池。所以这不是一般的Rule of Three violation;它有点不同。

快速浏览说复制逻辑是好的（如果可以的话，可以考虑使用std::vector来获取数据。如果你这样做，你可以丢掉大约1/4的代码。）而且最大的死亡点是不完整的默认构造函数。

w3::Text a;

将调用bare-bones默认构造函数

Text::Text() {

}

哪个不会将data初始化为nullptr。这会在const Text& Text::operator=(const Text& copyfrom)：

中导致问题

if (data != nullptr)
{
    delete[] data;
    entries = 0;
}

从未设置a=b; a.data时，不太可能是nullptr，并且会尝试释放它不拥有的存储空间。如果程序设法跛行通过它，它可以，它的状态现在无效，Crom只知道它什么时候会失败。

Text::Text(): entries(0), data(nullptr)
{

}

解决了这个问题。

也...

复制构造函数泄漏

Text::Text(const Text& copyfrom)
{
    data = nullptr; //The object is empty
    *this = copyfrom;
}

您如何知道数据是空的？没有测试，所以噗！如果那里有什么东西，现在就无法到达。但正如Paul McKenzie在上面指出的那样，根据Copy构造函数编写赋值运算符几乎总是更好。

移动赋值运算符有点难以理解。

Text&& Text::operator=(Text&& movefrom)

应该是

Text& Text::operator=(Text&& movefrom)

这意味着您不必使用this清除return std::move(*this);。只需return *this;

在析构函数中没有任何意义

data = nullptr;

该对象在该行之后立即被销毁，因此将data归零是浪费精力。

返回0之前主要崩溃

1 个答案: