【C++】string类中常用函数的模拟实现

1. string.h

#include<assert.h>namespace wch
{class string{public: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;}//若使用初始化列表初始化要注意：初始化顺序为声明顺序//构造函数无参对象初始化 string str;string(const char* str = "")//string(const char* str = "\0"){_size = strlen(str);_capacity = _size;_str = new char[_capacity + 1];strcpy(_str, str);}string(const string& s)//构造函数有参对象初始化 string str("abc");{_str = new char[s._capacity + 1];strcpy(_str, s._str);_size = s._size;_capacity = s._capacity;}~string(){delete[] _str;_str = nullptr;_size = _capacity = 0;}const char* c_str() const{return _str;}size_t size() const{return _size;}char& operator[](size_t pos){assert(pos < _size);return _str[pos];}const char& operator[](size_t pos) const{assert(pos < _size);return _str[pos];}void reserve(size_t n){//要加判断条件，因为当n <= _capacity时不做任何处理if (n > _capacity){char* tmp = new char[n + 1];strcpy(tmp, _str);delete[] _str;_str = tmp;_capacity = n;}}void push_back(char ch){if (_size == _capacity){// 2倍扩容reserve(_capacity == 0 ? 4 : _capacity * 2);}_str[_size] = ch;++_size;_str[_size] = '\0';}void append(const char* str){size_t len = strlen(str);if (_size + len > _capacity){// 至少扩容到_size + lenreserve(_size + len);}strcpy(_str + _size, str);_size += len;}string& operator+=(char ch)//末尾添加字符{push_back(ch);return *this;}string& operator+=(const char* str)//末尾添加字符串{append(str);return *this;}void insert(size_t pos, size_t n, char ch)//从下标pos位置开始向后插入n个字符ch{assert(pos <= _size);if (_size + n > _capacity){// 至少扩容到_size + nreserve(_size + n);}// 挪动数据/*int end = _size;while (end >= (int)pos)//整型提升有符号向无符号提升{_str[end + n] = _str[end];--end;}*/// 挪动数据size_t end = _size;while (end >= pos && end != npos){_str[end + n] = _str[end];--end;}for (size_t i = 0; i < n; i++){_str[pos + i] = ch;}_size += n;}void insert(size_t pos, const char* str){assert(pos <= _size);size_t len = strlen(str);if (_size + len > _capacity){// 至少扩容到_size + lenreserve(_size + len);}size_t end = _size;while (end >= pos && end != npos){_str[end + len] = _str[end];--end;}for (size_t i = 0; i < len; i++){_str[pos + i] = str[i];}_size += len;}void erase(size_t pos, size_t len = npos){assert(pos <= _size);if (len == npos || pos + len >= _size)//将pos后面的数据删完{_str[pos] = '\0';_size = pos;}else//删除pos到结尾的部分连续数据{size_t end = pos + len;while (end <= _size){_str[pos++] = _str[end++];}_size -= len;}}size_t find(char ch, size_t pos = 0)//找字符下标{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)//找字符串下标{assert(pos < _size);const char* ptr = strstr(_str + pos, str);if (ptr){return ptr - _str;}else{return npos;}}string substr(size_t pos = 0, size_t len = npos){assert(pos < _size);size_t n = len;if (len == npos || pos + len > _size){n = _size - pos;}string tmp;tmp.reserve(n);for (size_t i = pos; i < pos + n; i++){tmp += _str[i];}return tmp;}private:size_t _size;size_t _capacity;char* _str;public://const static size_t npos = -1; // 虽然可以这样用，但是不建议const static size_t npos;//const static double x = 1.1；//不支持除了int以外其他const static类型在类内定义并初始化};const size_t string::npos = -1;//const double string::x = 1.1;
};

2. Text.cpp

#define  _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
#include<string>
using namespace std;#include"string.h"void test_string1()
{wch::string s1("hello world");cout << s1.c_str() << endl;wch::string s2;cout << s2.c_str() << endl;for (size_t i = 0; i < s1.size(); i++){s1[i]++;}for (size_t i = 0; i < s1.size(); i++){cout << s1[i] << " ";}cout << endl;const wch::string s3("hello world");s3[0];//wch::string::const_iterator cit = s3.begin();auto cit = s3.begin();while (cit != s3.end()){//*cit += 1;cout << *cit << " ";++cit;}cout << endl;wch::string::iterator it = s1.begin();while (it != s1.end()){*it += 1;cout << *it << " ";++it;}cout << endl;for (auto ch : s1){cout << ch << " ";}cout << endl;
}void test_string2()
{wch::string s1("hello world");cout << s1.c_str() << endl;s1.push_back(' ');s1.push_back('#');s1.append("hello world");cout << s1.c_str() << endl;wch::string s2("hello world");cout << s2.c_str() << endl;s2 += ' ';s2 += '#';s2 += "hello world";cout << s2.c_str() << endl;
}void test_string3()
{wch::string s1("helloworld");cout << s1.c_str() << endl;s1.insert(5, 3, '#');cout << s1.c_str() << endl;s1.insert(0, 3, '#');cout << s1.c_str() << endl;wch::string s2("helloworld");s2.insert(5, "%%%%%");cout << s2.c_str() << endl;
}void test_string4()
{wch::string s1("helloworld");cout << s1.c_str() << endl;s1.erase(5, 3);cout << s1.c_str() << endl;s1.erase(5, 30);cout << s1.c_str() << endl;s1.erase(2);cout << s1.c_str() << endl;
}void test_string5()
{// 2118wch::string url = "ftp://www.baidu.com/?tn=65081411_1_oem_dg";size_t pos1 = url.find("://");cout << pos1 << endl;if (pos1 != wch::string::npos){wch::string protocol = url.substr(0, pos1);cout << protocol.c_str() << endl;}size_t pos2 = url.find('/', pos1 + 3);cout << pos2 << endl;if (pos2 != wch::string::npos){wch::string domain = url.substr(pos1 + 3, pos2 - (pos1 + 3));wch::string uri = url.substr(pos2 + 1);cout << domain.c_str() << endl;cout << uri.c_str() << endl;}
}int main()
{//test_string1();//test_string2();//test_string3();//test_string4();test_string5();return 0;
}