C++ Pascal 字符串错误。我在代码中找不到错误

Question

下面是我的代码，然后是错误消息。我将不胜感激任何帮助。谢谢你。作业如下：

” 修改提供的 String 类以在内部存储 Pascal 字符串，这些字符串是字符数组，以字符串中的多个字符开头，后跟这些字符，no 终止空字符。那就是：

• str 应该包含一个 Pascal 字符串。
• 应该包括在您的 Pascal 字符串实验室中创建的构造函数。 还应包含普通的 C 字符串构造函数，并且必须转换为 Pascal 字符串。
• c_str 函数必须转换回 C 字符串以向用户提供 C 字符串。在这个函数中为字符串分配内存是可以的。
• 考虑到内部字符串格式的更改，所有其他函数必须正确执行。
• 您可以不在内部将 C 字符串与 Pascal 字符串一起存储。

帕斯卡.cpp

// Pascal Main cpp


#include <iostream>
#include <algorithm>
#include "Pascal.h"
#include <exception>
using namespace std;
// Default constructor
String::String() {
    arr = new char[1];
    arr[0] = '\0';
    len = 0;
}

// Constructor. Converts a C-string to a String object
String::String(const char *s) {
    len = strlen(s);
    arr = new char[len + 1];
    std::copy(s, s + len + 1, arr);
}

// Copy constructor.
String::String(const String &obj) {
    len = obj.len;
    arr = new char[len + 1];
    std::copy(obj.arr, obj.arr + len + 1, arr);
}

// Move constructor.
String::String(String &&obj) {
    len = obj.len;
    arr = obj.arr;
    obj.arr = nullptr;
}

String::String(const char *str, bool pascal) {
    judge = pascal;
    if (judge) {
        len = strlen(str) - 1;
        const char *temp = str;
        arr = new char[len + 1];
        arr[0] = len + '0';
        for (int i = 1; i <= len; i++) {
            arr[i] = temp[i];
        }

    }
    else {
        len = strlen(str);
        arr = new char[len + 1];
        std::copy(str, str + len + 1, arr);
    }
}

// Destructor
String::~String() {
    if (arr != nullptr)
        delete[] arr;
}

// Assignment operator
String &String::operator=(const String &rhs) {
    delete[] arr;
    len = rhs.len;
    arr = new char[len + 1];
    std::copy(rhs.arr, rhs.arr + len + 1, arr);
    return *this;
}

// Move assignment operator
String &String::operator=(String &&rhs) {
    delete[] arr;
    len = rhs.len;
    arr = rhs.arr;
    rhs.arr = nullptr;
    return *this;
}


// Mutator operator[]
char &String::operator[](int index) {
    // check whether the index is within bounds
    if (index > len || index < 0)
        throw std::out_of_range("Index out of range");
    return arr[index];
}

// Accessor operator[]
char String::operator[](int index) const {
    // check whether the index is within bounds
    if (index > len || index < 0)
        throw std::out_of_range("Index out of range");
    return arr[index];
}

// Get the length (number of characters) of a String object
int String::length() const {
    return len;
}

bool operator==(const String &lhs, const String &rhs) {
    if (lhs.judge != rhs.judge) {
        cout << "can't compare";
    }
    return strcmp(lhs.arr, rhs.arr) == 0;
}

bool operator<(const String &lhs, const String &rhs) {
    if (lhs.judge != rhs.judge) {
        cout << "can't compare";
    }
    return strcmp(lhs.arr, rhs.arr) < 0;
}

// Friend functions for > comparison
bool operator>(const String &lhs, const String &rhs) {
    if (lhs.judge != rhs.judge) {
        cout << "can't compare";
    }
    return rhs < lhs;
}

// Friend functions for <= comparison
bool operator<=(const String &lhs, const String &rhs) {
    if (lhs.judge != rhs.judge) {
        cout << "can't compare";
    }
    return !(rhs < lhs);
}

// Friend functions for >= comparison
bool operator>=(const String &lhs, const String &rhs) {
    if (lhs.judge != rhs.judge) {
        cout << "can't compare";
    }
    return !(lhs  < rhs);
}

// Friend functions for != comparison
bool operator!=(const String &lhs, const String &rhs) {
    if (lhs.judge != rhs.judge) {
        cout << "can't compare";
    }
    return !(lhs == rhs);
}

//  Friend function for string concatination
String operator+(const String &lhs, const String &rhs) {
    if (lhs.judge == rhs.judge && lhs.judge == false) {
        int strLength = lhs.len + rhs.len + 1;
        char *tmpStr = new char[strLength];
        for (auto i = 0; i < lhs.len; ++i)
            tmpStr[i] = lhs.arr[i];
        for (auto i = 0; i <= rhs.len; ++i)
            tmpStr[lhs.len + i] = rhs.arr[i];
        String retStr(tmpStr);
        delete[] tmpStr;
        return retStr;
    }
    else if (lhs.judge == rhs.judge && lhs.judge == true) {
        int strLength = lhs.len + rhs.len + 1;
        char *tmp = new char[strLength];
        for (auto i = 1; i <= lhs.len; ++i)
            tmp[i] = lhs.arr[i];
        for (auto i = 1; i <= rhs.len; ++i)
            tmp[lhs.len + i] = rhs.arr[i];
        tmp[0] = (lhs.len + rhs.len) + '0';
        String retStr(tmp);
        delete[] tmp;
        return retStr;
    }
    else {
        return String("can't do that");
    }
}

// Return C style character string
const char* String::c_str() const {
    return arr;
}

//  Friend function for output
std::ostream& operator<<(std::ostream &out, const String &obj) {
    return out << obj.c_str();
}

帕斯卡.h

// Pascal Header File

#pragma once
#ifndef __MYSTRING_H__
#define __MYSTRING_H__

#include <iostream>

class String {
public:
    // Usage: String aStringObj; or String aStringObj();
    String();

    // Constructor. Converts a char* object to a String  object
    // Usage: String aStringObj("hello"); or String aStringObj = "hello";
    String(const char *s);

    // Copy and move constructors.
    // Usage: String aStringObject(anotherStringObj); or
    // String aStringObject = anotherStringObj;
    String(const String &s);
    String(const char *str, bool pascal);
    String(String&& obj);

    // Destructor
    ~String();

    // Assignment operator
    // Usage: aStringObject = anotherStringObj; or
    // aStringObject.operator=(anotherStringObj);
    String &operator=(const String &rhsObject);
    String& operator=(String&& rhs);

    // Mutator operator[]
    // Usage: aStringObject[1] = ’M’;
    char &operator[] (int index);

    // Accessor operator[]
    // Usage: char ch = aStringObject[1];
    char operator[] (int index) const;

    // Get the length (number of characters) of a String object
    // Usage: int len = aStringObject.Length();
    int length() const;

    // Friend functions for == comparison
    // Usage: if (aStringObject == anotherStringObj) {...} or
    //        if (aStringObject == "hello") {...} or
    //        if ("hello" == aStringObj) {...} or
    friend bool operator==(const String &lhsObject, const String &rhsObject);

    // The other five comparison operators
    // !=, <, >, <=, >= are similarly handled as in line 13.

    friend bool operator<(const String &lhsObject, const String &rhsObject);
    friend bool operator>(const String &lhsObject, const String &rhsObject);
    friend bool operator<=(const String &lhsObject, const String &rhsObject);
    friend bool operator>=(const String &lhsObject, const String &rhsObject);
    friend bool operator!=(const String &lhsObject, const String &rhsObject);

    // Friend function for string concatenation
    // Usage: StringOne = StringTwo + StringThree  or
    //        StringOne = "hello" + StringTwo  or
    //        StringOne = StringTwo + "hello"
    friend String operator+(const String &lhs, const String &rhs);

    // Return C style character string
    // Usage: const char *str = aStringObj.C_str();
    const char *c_str() const;

    // Friend function for output
    // Usage: cout << aStringObj;
    friend std::ostream &operator<<(std::ostream &out, const String &obj);

private:
    // arr implements the String object as a dynamic array
    char *arr;

    // len keeps track of the length
    int len;

    // judge weather the String is a c_string or a pascal_string
    bool judge;
};

#endif

编译时出现以下警告和错误：

严重性代码 描述 项目文件行抑制状态 警告 C4996 'std::_Copy_impl'：带有可能不安全的参数的函数调用 - 此调用依赖于调用者检查传递的值是否正确。要禁用此警告，请使用 -D_SCL_SECURE_NO_WARNINGS。请参阅有关如何使用 Visual C++ 'Checked Iterators' Pascal Assignment c:\program files (x86)\microsoft visual studio 14.0\vc\include\xutility 2229 的文档 严重性代码 描述 项目文件行抑制状态 错误 LNK1120 1 未解决的外部 Pascal 分配 C:\Users\Danielle\Documents\Visual Studio 2015\Projects\Pascal Assignment\Debug\Pascal Assignment.exe 1 严重性代码 描述 项目文件行抑制状态 错误 LNK2019 未解析的外部符号 _main 在函数“int __cdecl invoke_main(void)”(?invoke_main@@YAHXZ) Pascal 分配 C:\Users\Danielle\Documents\Visual Studio 2015\Projects\Pascal Assignment\MSVCRTD.lib(exe_main.对象）1

Answer 1

缺少 main 函数是因为您还没有定义一个函数，并且您正在编译为一个程序。这应该是一个库项目，或者应该有一个main 函数。 代码末尾的#endif 表示这是一个没有显示开头的标题。如果是这样，那么 y您需要一个单独的 .cpp 文件（例如）将您的 main 放入。

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在其他新闻中：

• 包含两个连续下划线的标识符，如 __MYSTRING_H__，是 保留 实现的，因此可能会导致问题。此外，保留以下划线后跟大写字母开头的标识符。使用例如只是MYSTRING_H。但是：

• 当您使用#pragma once 时，您不需要包含保护符号。

• 我还没有真正研究过代码，但除非你使用像 << 这样的操作，或者例如endl，在标题中，那么您不需要在标题中包含整个<iostream>。包含<iosfwd> 就足够了。这就是它的用途：精益且仅意味着相关类型的声明。您仍然需要在使用标准流的地方包含<iostream>，即在您的实现文件中。但此费用不计入客户端代码。