代码如下:

#include<iostream>
#include <cstring>
#define _CRT_SECURE_NO_WARNINGS
using namespace std;class String
{
public:String(){size = 0;str = new char[size + 1];str[0] = '\0';}String(const String &obj){size = obj.size;str = new char[size + 1];if (str == nullptr){cout << "Failed to apply for space" << endl;exit(1);}strcpy(str, obj.str);}String(const char *s){size = strlen(s);str = new char[size + 1];if (str == nullptr){cout << "Failed to apply for space" << endl;exit(1);}strcpy(str, s);}String substr(int pos, int length){String tmp;int len = size - pos >= length ? length : size - pos;tmp.size = len;tmp.str = new char[len + 1];for (int i = 0; i < len; i++){tmp.str[i] = str[i + pos];}tmp.str[len] = '\0';return tmp;}void insert(const String &obj, int pos){String tmp;tmp.size = obj.size + size;tmp.str = new char[tmp.size + 1];for (int i = 0; i < pos; i++){tmp.str[i] = str[i];}for (int i = pos; i < pos + obj.size; i++){tmp.str[i] = obj.str[i - pos];}for (int i = 0; i < size - pos; i++){tmp.str[i+pos + obj.size] = str[pos + i];}tmp.str[tmp.size] = '\0';delete[] str;str = tmp.str;size = tmp.size;tmp.str = nullptr;}void Delete(int pos, int length){String tmp;int len = size - pos >= length ? length : size - pos;tmp.size = size-len;tmp.str = new char[tmp.size + 1];int i = 0;while (i < pos){tmp.str[i] = str[i];i++;}int j = pos + len;while (j < size){tmp.str[i] = str[j];i++;j++;}tmp.str[i] = '\0';delete[] str;str = tmp.str;size = tmp.size;tmp.str = nullptr;}int strsize(){return size;}String &operator=(String obj){if (this->str == obj.str) return *this;if (str != nullptr) delete[] str;size = obj.size;str = new char[size + 1];strcpy(str, obj.str);return *this;}String &operator=(const char *s){if (this->str == s) return *this;if (str != nullptr) delete[] str;size = strlen(s);str = new char[size + 1];strcpy(str, s);return *this;}String operator+(String &obj){String tmp;tmp.size = size + obj.size;tmp.str = new char[tmp.size + 1];for (int i = 0; i < size; i++){tmp.str[i] = str[i];}for (int i = size; i < tmp.size; i++){tmp.str[i] = obj.str[i - size];}tmp.str[tmp.size] = '\0';return tmp;}String operator+(const char *s){String tmp;tmp.size = strlen(s) + size;tmp.str = new char[tmp.size + 1];for (int i = 0; i < size; i++){tmp.str[i] = str[i];}for (int i = size; i < tmp.size; i++){tmp.str[i] = s[i - size];}tmp.str[tmp.size] = '\0';return tmp;}friend String operator+(const char *s, String &obj);friend ostream &operator<<(ostream &os, const String &obj);friend istream &operator>>(istream &is, String &obj);bool operator ==(const String &b){if (size != b.size) return false;for (int i = 0; i < size; i++){if (str[i] != b.str[i]) return false;}return true;}bool operator !=(const String &b){if (*this == b) return false;return true;}char &operator[](int x){if ( x> size) {cout << "The value passed in is out of bounds" << endl;exit(1);}return str[x];}const char &operator[](int x) const{if (x > size){cout << "The value passed in is out of bounds" << endl;exit(1);}return str[x];}~String(){if (str != nullptr)delete[] str;}char *str;int size;
};String operator+(const char *s, String &obj)
{String tmp;int len = strlen(s);tmp.size = strlen(s) + obj.size;tmp.str = new char[tmp.size + 1];for (int i = 0; i < len; i++){tmp.str[i] = s[i];}for (int i = len; i < tmp.size; i++){tmp.str[i] = obj.str[i - len];}tmp.str[tmp.size] = '\0';return tmp;
}ostream &operator<<(ostream &os, const String &obj)
{os << obj.str;return os;
}int main()
{String s("hello");String s1(s);cout << s1.strsize() << endl;cout << s1 << endl;s1.Delete(2, 3);cout << s1 << endl;s1.insert("llo", 2);cout << s1 << endl;cout << s1 + s << endl;cout << s[1] << endl;return 0;
}

测试结果: