C++自己封装一个简易的String类

C++面试题（二）——自己实现一个String类_普通网友的博客-CSDN博客

关于C++ 友元函数重载cin,cout,和+运算符的方法_jacka03的博客-CSDN博客

C++ 重载cout_快乐的提千万的博客-CSDN博客_重载cout

C++ getline函数用法_临渊慎行的博客-CSDN博客_c++ getline

c++中getline的用法_IT_xiaolaoshu的博客-CSDN博客_c++ getline

包含：

拷贝构造函数、析构函数、拷贝赋值函数、

重载 +=运算符、数组索引运算符[]、输入输出运算符、

实现size()函数、

#pragma once
//String.h
#include 
using namespace std;
class String {
public:
    String(const String& str) :capacity(str.capacity), length(str.length) {//拷贝构造函数1
        s = new char[capacity+4];
        memcpy(s, str.s, length);
    }

    String(const char* ch) :capacity(defaultCapacity), length(strlen(ch)) {//拷贝构造函数2
        //cout << length << endl;
        if (length > capacity) {
            capacity = length * 2;
        }
        s = new char[capacity + 4];
        memcpy(s, ch, length);
    }
    String() :String(""){
    }
    ~String() {
        try {
            delete[] s;
        }
        catch (exception e) {
            cerr << e.what() << endl;
        }
        
    }
    String& operator=(String& str) {//拷贝赋值函数1
        length = str.length;
        if (length >= capacity) {
            capacity = length * 2;
            delete[] s;
            s = new char[capacity + 4];
        }
        memcpy(s, str.s, length);
        return *this;
    }
    String& operator=(const char* ch) {//拷贝赋值函数2
        length = strlen(ch);
        if (length >= capacity) {
            capacity = length * 2;
            delete[] s;
            s = new char[capacity+4];
        }
        memcpy(s, ch, length);
        return *this;
    }
    
    String& operator+=(String& str) {
        length += str.length;
        if (length >= capacity) {
            capacity = length * 2;
            char* temp = s;
            s = new char[capacity + 4];
            memcpy(s, temp, length);
            delete[] temp;
        }
        memcpy(s + length - str.length, str.s, length);
        return *this;
    }
    
    String& operator+=(const char* ch) {
        return *this += String(ch);
    }
    char operator[](int i) {//数组索引运算符
        if (i >= length) {
            throw runtime_error("越界");
        }
        return s[i];
    }
    int size() {//字符串长度
        return length;
    }

private:
    int length;
    int capacity;
    char* s;
    int defaultCapacity = 2;//默认字符串容量
    friend ostream& operator<<(ostream& out, String& str) {// ostream是系统自带cout的类型
        for (int i = 0; i < str.length; ++i) {
            out << str[i];
        }
        return out;
    }
    friend istream& operator>>(istream& in, String& str) {// istream是系统自带cin的类型
        //char* ch = new char[1024]{};
        char ch[1024]{};
        in.getline(ch, 1024);
        int len = 0;
        for (int i = 0; i < 1024; ++i) {
            if (ch[i] == 0) {//读取输入长度
                len = i+1;
                break;
            }
        }
       // char* temp = new char[len+1];
        char temp[1024];       
        try {
            memcpy(temp, ch, len);//加这个可以使strlen读到正确的字符串长度
            str = temp;//赋值给str
        }
        catch (exception e) {
            cout << e.what()< 
#include 
#include "String.h"
using namespace std;

int main()
{
    String s= "123123";// = new char[6];//测试拷贝构造函数
    cout << s.size() << endl;//测试容量
    cout << sizeof("123") << endl;
    cout << s[2] << endl;//测试数组索引函数
    cout << s << endl;
    s += "098";//测试+=函数
    cout << s << endl;
    s = "333334";//测试拷贝赋值函数
    cout << s << endl;
    cin >> s;//测试输入函数
    cout << s << endl;
    s += "098";//测试+=函数
    cout << s << endl;
    return 0;
}
 
 
在实现的过程中还遇到了HEAP CORRUPTION DETECTED的错误的错误，参考了：
 
Heap Corruption Detected解决方法__北方的雪_的博客-CSDN博客
 
C++调试遇到HEAP CORRUPTION DETECTED的错误与解决方法_BlueBallonBird的博客-CSDN博客
 
然后在new的时候将capacity改成capacity+4便解决问题了，具体原因还未查出,应该是没考虑全字符串的尾巴还有给空格的问题。
 
改进后：
 
#pragma once
//String.h
#include 
using namespace std;
class String {
public:
    String(const String& str) :capacity(str.capacity), length(str.length) {//拷贝构造函数1
        s = new char[capacity];
        memcpy(s, str.s, length);
    }

    String(const char* ch) :capacity(defaultCapacity), length(strlen(ch)) {//拷贝构造函数2
        //cout << length << endl;
      //  cout << defaultCapacity << endl;
        if (length +1>= capacity) {
            capacity = (length + 1) * 2;
        }
        s = new char[capacity];
        memcpy(s, ch, length);
    }
    String() :String(""){
    }
    ~String() {
        try {
            delete[] s;
        }
        catch (exception e) {
            cerr << e.what() << endl;
        }
        
    }
    String& operator=(String& str) {//拷贝赋值函数1
        length = str.length;
        if (length + 1 >= capacity) {
            capacity = (length+1) * 2;
            delete[] s;
            s = new char[capacity];
        }
        memcpy(s, str.s, length);
        return *this;
    }
    String& operator=(const char* ch) {//拷贝赋值函数2
        length = strlen(ch);
        if (length +1>= capacity) {
            capacity = (length + 1) * 2;
            delete[] s;
            cout << length <<"aaaa" <= capacity) {
            capacity = (length + 1) * 2;
            char* temp = s;
            s = new char[capacity];/
            memcpy(s, temp, length);
            delete[] temp;
        }
        memcpy(s + length - str.length, str.s, length);
        return *this;
    }
    
    String& operator+=(const char* ch) {
        return *this += String(ch);
    }
    char operator[](int i) {//数组索引运算符
        if (i >= length) {
            throw runtime_error("越界");
        }
        return s[i];
    }
    int size() {//字符串长度
        return length;
    }

private:
    int length;
    int capacity;
    char* s;
    int defaultCapacity = 3;//默认字符串容量
    friend ostream& operator<<(ostream& out, String& str) {// ostream是系统自带cout的类型
        for (int i = 0; i < str.length; ++i) {
            out << str[i];
        }
        return out;
    }
    friend istream& operator>>(istream& in, String& str) {// istream是系统自带cin的类型
        //char* ch = new char[1024]{};
        char ch[1024]{};
        in.getline(ch, 1024);
        int len = 0;
        for (int i = 0; i < 1023; ++i) {//最后一位为空格
            if (ch[i] == 0) {//读取输入长度
                len = i+1;
                break;
            }
        }
       // char* temp = new char[len+1];
        char temp[1024];       
        try {
            memcpy(temp, ch, len);//加这个可以使strlen读到正确的字符串长度,注意-1
            str = temp;//赋值给str
        }
        catch (exception e) {
            cout << e.what()<