string的模拟实现
string的模拟实现（重点）
头文件：
cpp
#pragma once
#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
#include<string>
#include<assert.h>
using namespace std;
namespace bit
{
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;
}
/*string()
:_str(new char[1]{'\0'})
,_size(0)
,_capacity(0)
{}*/
// 短小频繁调用的函数，可以直接定义到类里面，默认是inline
string(const char* str = "")
{
_size = strlen(str);
// _capacity不包含\0
_capacity = _size;
_str = new char[_capacity + 1];
strcpy(_str, str);
}
// 深拷贝问题
//
// s2(s1)
//string(const string& s)
//{
// _str = new char[s._capacity + 1];
// strcpy(_str, s._str);
// _size = s._size;
// _capacity = s._capacity;
//}
// 深拷贝问题的优化
// 现代写法(非常重要）
void swap(string& s)
{
std::swap(_str, s._str);
std::swap(_size, s._size);
std::swap(_capacity, s._capacity);
}
string(const string& s)
{
string tmp(s._str);
swap(tmp)
}
// s2 = s1
// s1 = s1
string& operator=(const string& s)
{
if (this != &s)
{
string tmp(s._str);
swap(tmp);
}
return *this;
}
~string()
{
if (_str)
{
delete[] _str;
_str = nullptr;
_size = _capacity = 0;
}
}
const char* c_str() const
{
return _str;
}
void clear()//不释放空间，清数据
{
_str[0] = '\0';
_size = 0;
}
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];
}
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, size_t len = npos);
private:
char* _str = nullptr;
size_t _size = 0;
size_t _capacity = 0;
static const size_t npos = -1;
//static const size_t npos;
};
bool operator<(const string& s1, const string& s2);
bool operator<=(const string& s1, const string& s2);
bool operator>(const string& s1, const string& s2);
bool operator>=(const string& s1, const string& s2);
bool operator==(const string& s1, const string& s2);
bool operator!=(const string& s1, const string& s2);
ostream& operator<<(ostream& out, const string& s);
istream& operator>>( istream& in, string& s);
}源文件：
cpp
#include"string.h"
namespace bit
{
const size_t string::npos = -1;
void test_string1()
{
string st;
string st1("hh");
cout << st.c_str() << endl;
cout<< st1.c_str() << endl;
string s1("hello world");
string::iterator it = s1.begin();
while (it != s1.end())
{
cout << *it;
it++;
}
for (auto ch : s1 )
{
cout << ch << " ";
}
cout << endl;
cout << endl;
}
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)
{
reserve(_capacity == 0 ? 4 : _capacity * 2);
}
_str[_size] = ch;
++_size;
_str[_size] = '\0';
}
string& string::operator+=(char ch)
{
push_back(ch);
return (*this);
}
string& string::operator+=(const char* str)
{
append(str);
return *this;
}
void string::append(const char* str)
{
size_t len = strlen(str);
if (_size + len > _capacity)
{
reserve(_size + len > 2 * _capacity ? _size + len : 2 * _capacity);
}
strcpy(_str + _size, str);
_size += len;
}
void string::insert(size_t pos, char ch)
{
assert(pos <= _size);
if (_size == _capacity)
{
reserve(_capacity == 0 ? 4 : _capacity * 2);
}
// 挪动数据
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* s)
{
assert(pos <= _size);
size_t len = strlen(s);
if (_size + len > _capacity)
{
// 大于2倍，需要多少开多少，小于2倍按2倍扩
reserve(_size + len > 2 * _capacity ? _size + len : 2 * _capacity);
}
size_t end = _size + len;
while (end > pos + len - 1)
{
_str[end] = _str[end - len];
--end;
}
for (size_t i = 0; i < len; i++)
{
_str[pos + i] = s[i];
}
_size += len;
}
void string::erase(size_t pos, size_t len )
{
if (len > _size - pos)
{
_str[pos] = '\0';
_size = pos;
}
else
{
for (size_t i = pos + len; i < _size; i++)
{
_str[i - len] = _str[i];
}
_str -= 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(char* str, size_t pos )
{
assert(pos < _size);
const char*ptr = strstr(str + pos, str);
if (ptr == nullptr)
{
return npos;
}
else
{
return ptr - str;
}
}
string string::substr(size_t pos, size_t len)//取子串
{
assert(pos < _size);
if (len > _size - pos)
{
len = _size - pos;
}
string sub;
sub.reserve(len);
for (size_t i = 0; i < len; i++)
{
sub += _str[pos + i];
}
return sub;
}
bool operator==(const string& s1, const string& s2)
{
return strcmp(s1.c_str(), s2.c_str()) == 0;
}
bool operator<(const string& s1, const string& s2)
{
return strcmp(s1.c_str(), s2.c_str())<0;
}
bool operator<=(const string& s1, const string& s2)
{
return s1 < s2 || s1 == s2;
}
bool operator>(const string& s1, const string& s2)
{
return !(s1 <= s2);
}
bool operator>=(const string& s1, const string& s2)
{
return !(s1 < s2);
}
bool operator!=(const string& s1, const string& s2)
{
return !(s1 == s2);
}
ostream& operator<<(ostream& out, const string& s)
{
for (auto ch : s)
{
out << ch;
}
return out;
}
istream& operator>>( istream& in, string& s)
{
s.clear();
const int N = 256;
char buff[N];
char ch;
in >> ch;
int i = 0;
ch = in.get();
while (ch != ' ' && ch != '\n')
{
buff[i++] = ch;
if (i == N - 1)
{
buff[i] = '\0';
s += buff;
i = 0;
}
ch = in.get();//*
}
if (i > 0)
{
buff[i] = '\0';
s += buff;
}
return in;
}
}