代码如下:

#pragma once
#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <assert.h>
#include <cstring>
using namespace std;class String
{
public:String(const char *str = ""){assert(str != nullptr);_size = strlen(str);_str = new char[_size + 1];_capacity = _size;strcpy(_str, str);}String(const String &s) :_str(nullptr), _size(0), _capacity(0){String tmp(s._str);Swap(tmp);}void Swap(String &s){swap(_str, s._str);swap(_size, s._size);swap(_capacity, s._capacity);}String &operator=(String s){if (this != &s){Swap(s);}return *this;}~String(){if (_str != nullptr){delete[]_str;_str = nullptr;}}size_t size() const{return _size;}size_t capacity()const{return _capacity;}char &operator[](size_t pos){assert(pos < _size);return _str[pos];}const char &operator[](size_t pos) const{assert(pos < _size);return _str[pos];}typedef char *iterator;typedef const char *const_iterator;iterator begin(){return _str;}iterator end(){return _str + _size;}const_iterator begin()const{return _str;}const_iterator end()const{return _str + _size;}void reserve(size_t n){if (n > _capacity){char *tmp = new char[n + 1];strcpy(tmp, _str);delete[] _str;_str = tmp;_capacity = n;}}void push_back(const char &ch){if (_size == _capacity){size_t newCapcity = _capacity == 0 ? 15 : 2 * _capacity;reserve(newCapcity);}_str[_size++] = ch;_str[_size] = '\0';}void resize(size_t n, const char &ch = '\0'){if (n > _capacity){reserve(n);}if (n > _size)memset(_str + _size, ch, (n - _size) * sizeof(char));_size = n;_str[_size] = '\0';}void append(const char *str){int len = strlen(str);if (_size + len > _capacity){reserve(_size + len);}memcpy(_str + _size, str, sizeof(char)*len);_size += len;_str[_size] = '\0';}String &operator+=(const String &str){append(str._str);return *this;}String &operator+=(const char *str){append(str);return *this;}String &operator+=(const char ch){push_back(ch);return *this;}void insert(size_t pos, const char &ch){assert(pos <= _size);if (_size == _capacity){size_t newCapacity = _capacity == 0 ? 15 : 2 * _capacity;reserve(newCapacity);}size_t end = _size + 1;while (end > pos){_str[end] = _str[end - 1];--end;}_str[pos] = ch;++_size;}void insert(size_t pos, const char *str){assert(pos <= _size);int len = strlen(str);if (_size + len >= _capacity){reserve(_size + len);}size_t end = _size + len;while (end > pos + len - 1){_str[end] = _str[end - len];--end;}memcpy(_str + pos, str, sizeof(char)*len);_size += len;}void erase(size_t pos, size_t len){assert(pos < _size);if (pos + len >= _size){_size = pos;_str[_size] = '\0';}else{size_t start = pos + len;while (start <= _size){_str[pos++] = _str[start];++start;}_size -= len;}}size_t find(const char &ch, size_t pos = 0){assert(pos < _size);for (size_t i = pos; i < _size; i++){if (_str[i] == ch){return i;}}return npos;}size_t find(const char *str, size_t pos = 0){char *ptr = strstr(_str, str);if (ptr != nullptr){return ptr - _str;}return npos;}private:char *_str;size_t _size;size_t _capacity;static const size_t npos;
};const size_t String::npos = -1;String  operator+(const String &str1, const String &str2)
{String tmp = str1;tmp += str2;return tmp;
}String  operator+(const String &str1, const char *str2)
{String tmp = str1;tmp += str2;return tmp;
}String operator+(const char &ch, const String &str1)
{String tmp = str1;tmp += ch;return tmp;
}ostream &operator<<(ostream &out, const String &str)
{for (const auto &ch : str){cout << ch;}return out;
}istream &operator>>(istream &in, String &str)
{char ch;while (ch = getchar()){if (ch == ' ' || ch == '\n' || ch == '\t'){break;}str += ch;}return in;
}

测试代码如下:

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include "String.h"using namespace std;int main(){String str = ("Hello Wecccccccc");cout << str << endl;String str1 = str;cout << str1 << endl;for (int i = 0; i < str1.size(); i++){cout << str[i] << " ";}cout << endl;for (const auto&ch : str){cout << ch << " ";}cout << endl;String::iterator it = str.begin();while (it != str.end()){cout << *it << " ";it++;}cout << endl;cout << "str size = " << str.size() << " " << "str capacity = " << str.capacity() << endl;str.reserve(20);cout << "str size = " << str.size() << " " << "str capacity = " << str.capacity() << endl;str.push_back('N');str.push_back('N');str.push_back('N');str.push_back('N');str.push_back('N');cout << str << endl;String str3 = "Weccccc";str3.resize(3);cout << str3 << endl;str3.resize(5, 'a');cout << str3 << endl;str3.resize(10, 'b');cout << str3 << endl;str3.append(" hello");cout << str3 << endl;String str4 = "We";String str5 = "cccccccc";str4 += str5;cout << str4 << endl;cout << str4 + str5 << endl;String str6;str6 = 'W' + str4+"123";cout << str6 << endl;String str7 = "abc";str7.insert(0, '1');cout << str7 << endl;str7.insert(1, '2');cout << str7 << endl;str7.insert(5, "35");cout << str7 << endl;str7.erase(0, 2);cout << str7 << endl;str7.erase(4, 1);cout << str7 << endl;str7.erase(1, 2);cout << str7 << endl;int pos = str7.find('3');cout << pos << endl;pos = str7.find('b');cout << pos << endl;return 0;}

测试结果: