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string构造

string::string(const char* str):_size(strlen(str))
{_str = new char[_size + 1];_capacity = _size;strcpy(_str, str);
}// s2(s1)
string::string(const string& s)
{_str = new char[s._capacity + 1];strcpy(_str, s._str);_size = s._size;_capacity = s._capacity;
}// s1 = s3
// s1 = s1
string& string::operator=(const string& s)
{if (this != &s){char* tmp = new char[s._capacity + 1];strcpy(tmp, s._str);delete[] _str;_str = tmp;_size = s._size;_capacity = s._capacity;}return *this;
}string::~string()
{delete[] _str;_str = nullptr;_size = _capacity = 0;
}

string容量操作

const char* string::c_str() const
{return _str;
}size_t string::size() const
{return _size;
}void string::reserve(size_t n)
{if (n > _capacity){char* tmp = new char[n + 1];strcpy(tmp, _str);delete[] _str;_str = tmp;_capacity = n;}
}

string类对象的访问和遍历操作

char& string::operator[](size_t pos)
{assert(pos < _size);return _str[pos];
}const char& string::operator[](size_t pos) const
{assert(pos < _size);return _str[pos];
}

const size_t string::npos = -1;string::iterator string::begin()
{return _str;
}string::iterator string::end()
{return _str + _size;
}string::const_iterator string::begin() const
{return _str;
}string::const_iterator string::end() const
{return _str + _size;
}size_t string::find(char ch, size_t pos)
{for (size_t i = pos; i < _size; i++){if (_str[i] == ch){return i;}}return npos;
}size_t string::find(const char* sub, size_t pos)
{char* p = strstr(_str + pos, sub);return  p - _str;
}

string类对象的修改操作

void string::push_back(char ch)
{/*if (_size == _capacity){size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;reserve(newcapacity);}_str[_size] = ch;_str[_size + 1] = '\0';++_size;*/insert(_size, ch);
}// "hello"  "xxxxxxxxxxxxx"
void string::append(const char* str)
{/*size_t len = strlen(str);if (_size + len > _capacity){reserve(_size + len);}strcpy(_str+_size, str);_size += len;*/insert(_size, str);
}string& string::operator+=(char ch)
{push_back(ch);return *this;
}string& string::operator+=(const char* str)
{append(str);return *this;
}void string::insert(size_t pos, char ch)
{assert(pos <= _size);if (_size == _capacity){size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;reserve(newcapacity);}/*int end = _size;while (end >= (int)pos){_str[end + 1] = _str[end];--end;}*/size_t end = _size + 1;while (end > pos){_str[end] = _str[end - 1];--end;}_str[pos] = ch;++_size;
}void string::insert(size_t pos, const char* str)
{assert(pos <= _size);size_t len = strlen(str);if (_size + len > _capacity){reserve(_size + len);}/*int end = _size;while (end >= (int)pos){_str[end + len] = _str[end];--end;}*/size_t end = _size + len;while (end > pos + len - 1){_str[end] = _str[end - len];--end;}memcpy(_str + pos, str, len);_size += len;
}// 17:10
void string::erase(size_t pos, size_t len)
{assert(pos < _size);// len大于前面字符个数时，有多少删多少if (len >= _size - pos){_str[pos] = '\0';_size = pos;}else{strcpy(_str + pos, _str + pos + len);_size -= len;}
}
// s1.swap(s3)
void string::swap(string& s)
{std::swap(_str, s._str);std::swap(_size, s._size);std::swap(_capacity, s._capacity);
}string string::substr(size_t pos, size_t len)
{// len大于后面剩余字符，有多少取多少if (len > _size - pos){string sub(_str + pos);return sub;}else{string sub;sub.reserve(len);for (size_t i = 0; i < len; i++){sub += _str[pos + i];}return sub;}
}

其他函数

bool string::operator<(const string& s) const{return strcmp(_str, s._str) < 0;}bool string::operator>(const string& s) const{return !(*this <= s);}bool string::operator<=(const string& s) const{return *this < s || *this == s;}bool string::operator>=(const string& s) const{return !(*this < s);}bool string::operator==(const string& s) const{return strcmp(_str, s._str) == 0;}bool string::operator!=(const string& s) const{return !(*this == s);}

void string::clear()
{_str[0] = '\0';_size = 0;
}istream& operator>> (istream& is, string& str)
{str.clear();char ch = is.get();while (ch != ' ' && ch != '\n'){str += ch;ch = is.get();}return is;
}ostream& operator<< (ostream& os, const string& str)
{for (size_t i = 0; i < str.size(); i++){os << str[i];}return os;
}

总结

string.h

#pragma once#include<iostream>
#include<assert.h>
using namespace std;namespace bit
{class string{public:typedef char* iterator;typedef const char* const_iterator;iterator begin();iterator end();const_iterator begin() const;const_iterator end() const;//string();string(const char* str = "");string(const string& s);string& operator=(const string& s);~string();const char* c_str() const;size_t size() const;char& operator[](size_t pos);const char& operator[](size_t pos) const;void reserve(size_t n);void push_back(char ch);void append(const char* str);string& operator+=(char ch);string& operator+=(const char* str);void insert(size_t pos, char ch);void insert(size_t pos, const char* str);void erase(size_t pos = 0, size_t len = npos);size_t find(char ch, size_t pos = 0);size_t find(const char* str, size_t pos = 0);void swap(string& s);string substr(size_t pos = 0, size_t len = npos);bool operator<(const string& s) const;bool operator>(const string& s) const;bool operator<=(const string& s) const;bool operator>=(const string& s) const;bool operator==(const string& s) const;bool operator!=(const string& s) const;void clear();private:// char _buff[16];char* _str;size_t _size;size_t _capacity;//  //const static size_t npos = -1;// ?//const static double N = 2.2;const static size_t npos;};istream& operator>> (istream& is, string& str);ostream& operator<< (ostream& os, const string& str);
}

string.cpp

//string::string()//{//	_str = new char[1]{'\0'};//	_size = 0;//	_capacity = 0;//}string::iterator string::begin(){return _str;}string::iterator string::end(){return _str + _size;}string::const_iterator string::begin() const{return _str;}string::const_iterator string::end() const{return _str + _size;}string::string(const char* str):_size(strlen(str)){_str = new char[_size + 1];_capacity = _size;strcpy(_str, str);}// s2(s1)string::string(const string& s){_str = new char[s._capacity + 1];strcpy(_str, s._str);_size = s._size;_capacity = s._capacity;}// s1 = s3// s1 = s1string& string::operator=(const string& s){if (this != &s){char* tmp = new char[s._capacity + 1];strcpy(tmp, s._str);delete[] _str;_str = tmp;_size = s._size;_capacity = s._capacity;}return *this;}string::~string(){delete[] _str;_str = nullptr;_size = _capacity = 0;}const char* string::c_str() const{return _str;}size_t string::size() const{return _size;}char& string::operator[](size_t pos){assert(pos < _size);return _str[pos];}const char& string::operator[](size_t pos) const{assert(pos < _size);return _str[pos];}void string::reserve(size_t n){if (n > _capacity){char* tmp = new char[n + 1];strcpy(tmp, _str);delete[] _str;_str = tmp;_capacity = n;}}void string::push_back(char ch){/*if (_size == _capacity){size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;reserve(newcapacity);}_str[_size] = ch;_str[_size + 1] = '\0';++_size;*/insert(_size, ch);}// "hello"  "xxxxxxxxxxxxx"void string::append(const char* str){/*size_t len = strlen(str);if (_size + len > _capacity){reserve(_size + len);}strcpy(_str+_size, str);_size += len;*/insert(_size, str);}string& string::operator+=(char ch){push_back(ch);return *this;}string& string::operator+=(const char* str){append(str);return *this;}void string::insert(size_t pos, char ch){assert(pos <= _size);if (_size == _capacity){size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;reserve(newcapacity);}/*int end = _size;while (end >= (int)pos){_str[end + 1] = _str[end];--end;}*/size_t end = _size + 1;while (end > pos){_str[end] = _str[end - 1];--end;}_str[pos] = ch;++_size;}void string::insert(size_t pos, const char* str){assert(pos <= _size);size_t len = strlen(str);if (_size + len > _capacity){reserve(_size + len);}/*int end = _size;while (end >= (int)pos){_str[end + len] = _str[end];--end;}*/size_t end = _size + len;while (end > pos + len - 1){_str[end] = _str[end - len];--end;}memcpy(_str + pos, str, len);_size += len;}// 17:10void string::erase(size_t pos, size_t len){assert(pos < _size);// len大于前面字符个数时，有多少删多少if (len >= _size - pos){_str[pos] = '\0';_size = pos;}else{strcpy(_str + pos, _str + pos + len);_size -= len;}}size_t string::find(char ch, size_t pos){for (size_t i = pos; i < _size; i++){if (_str[i] == ch){return i;}}return npos;}size_t string::find(const char* sub, size_t pos){char* p = strstr(_str + pos, sub);return  p - _str;}// s1.swap(s3)void string::swap(string& s){std::swap(_str, s._str);std::swap(_size, s._size);std::swap(_capacity, s._capacity);}string string::substr(size_t pos, size_t len){// len大于后面剩余字符，有多少取多少if (len > _size - pos){string sub(_str + pos);return sub;}else{string sub;sub.reserve(len);for (size_t i = 0; i < len; i++){sub += _str[pos + i];}return sub;}}bool string::operator<(const string& s) const{return strcmp(_str, s._str) < 0;}bool string::operator>(const string& s) const{return !(*this <= s);}bool string::operator<=(const string& s) const{return *this < s || *this == s;}bool string::operator>=(const string& s) const{return !(*this < s);}bool string::operator==(const string& s) const{return strcmp(_str, s._str) == 0;}bool string::operator!=(const string& s) const{return !(*this == s);}void string::clear(){_str[0] = '\0';_size = 0;}istream& operator>> (istream& is, string& str){str.clear();char ch = is.get();while (ch != ' ' && ch != '\n'){str += ch;ch = is.get();}return is;}ostream& operator<< (ostream& os, const string& str){for (size_t i = 0; i < str.size(); i++){os << str[i];}return os;}