当我们已经了解了string类的各种函数及其使用，我们可以用已学的C++知识来模拟实现一下string类，实现一下string类中相关的函数
cpp
#pragma once
#include<iostream>
using namespace std;
#include<assert.h>
namespace bit
{
class string
{
friend ostream& operator<<(ostream& out, const bit::string& s);
friend istream& operator>>(istream& in, bit::string& s);
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(const char* str="")
{
_size = strlen(str);
_capacity = _size;
_str = new char[_capacity+1];
memcpy(_str, str,_size+1);
}
string(const string& s)
{
_str = new char[s._capacity +1];
_size = s._size;
_capacity = s._capacity;
memcpy(_str, s._str,_size);
}
const char* c_str() const
{
return _str;
}
size_t size()
{
return _size;
}
size_t capacity()
{
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)
{
if (n > _capacity)
{
char* tmp = new char[n+1];
strcpy(tmp, _str);
_capacity = n+1;
delete[] _str;
_str = tmp;
}
}
void push_back(const char ch)
{
if (_size + 1 > _capacity)
{
reserve(_capacity == 0 ? 4 : _capacity *= 2);
}
_str[_size] = ch;
_size += 1;
_str[_size] = '\0';
}
void append(const char* str)
{
if (_size + strlen(str) > _capacity)
{
reserve(_size + strlen(str));
}
memcpy(_str + _size, str, _size + strlen(str));
_size += strlen(str);
}
string& operator+=(const char ch)
{
push_back(ch);
return *this;
}
string& operator+=(const char* str)
{
append(str);
return *this;
}
void swap(string& s)
{
std::swap(_str, s._str);
std::swap(_size, s._size);
std::swap(_capacity, s._capacity);
}
string& operator=(string str)
{
swap(str);
return *this;
}
void insert(size_t pos,size_t n,const char ch)
{
assert(pos <= _size);
if (_size + n > _capacity)
{
reserve(_size + n);
}
size_t tmp = _size;
while (tmp>=pos&&tmp!=npos)
{
_str[tmp + n] = _str[tmp];
tmp--;
}
while (n--)
{
_str[pos] = ch;
pos++;
}
}
void insert(size_t pos, const char* str)
{
assert(pos <= _size);
size_t n = strlen(str);
if (_size + n > _capacity)
{
reserve(_size + n);
}
size_t tmp = _size;
while (tmp >= pos && tmp != npos)
{
_str[tmp + n] = _str[tmp];
tmp--;
}
for (size_t i = 0; i < n; i++)
{
_str[pos] = str[i];
pos++;
}
}
void resize(size_t n, char c = '\0')
{
if (n > _capacity)
{
reserve(n);
int len = n - _size;
while (len--)
_str += c;
}
else
{
if (n > _size)
{
int len = n - _size;
while (len--)
_str += c;
}
else
{
_size = n;
}
}
}
void erase(size_t pos, size_t n = npos)
{
assert(pos <= _size);
if (n == npos || pos + n >= _size)
{
_str[pos] = '\0';
_size = pos;
}
else
{
while (n--)
{
for (size_t i = pos; i < _size; i++)
{
_str[i] = _str[i + 1];
}
//pos++;
_size--;
}
}
}
string& clear()
{
_size = 0;
_str += '\0';
return *this;
}
size_t find(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)
{
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 n = npos)
{
string tmp;
if (pos+n >= _size || n == npos)
{
n = _size - pos;
}
tmp.reserve(n);
for (size_t i = pos; i < pos+n; i++)
{
tmp += _str[i];
}
return tmp;
}
bool empty(const string& s)const
{
if (s._size == 0)
return true;
else
return false;
}
bool operator<(const string& s)
{
int min = s._size <= _size ? s._size : _size;
for (int i = 0; i < min; i++)
{
if (s[i] > _str[i])
return true;
if (s[i] < _str[i])
return false;
}
if (_size < s._size)
return true;
else
return false;
}
bool operator<=(const string& s)
{
int min = s._size <= _size ? s._size : _size;
for (int i = 0; i < min; i++)
{
if (s[i] > _str[i])
return true;
if (s[i] < _str[i])
return false;
}
if (_size <= s._size)
return true;
else
return false;
}
bool operator>(const string& s)
{
if ((*this<=s))
return false;
else
return true;
}
bool operator>=(const string& s)
{
if (*this == s)
return true;
else if (*this > s)
return true;
else
return false;
}
bool operator==(const string& s)
{
if (_size != s._size)
return false;
else
{
if ((*this < s) || (*this > s))
return false;
else
return true;
}
}
bool operator!=(const string& s)
{
if (*this == s)
return false;
else
return true;
}
~string()
{
delete[] _str;
_str = nullptr;
_size = _capacity = 0;
}
private:
size_t _size;
size_t _capacity;
char* _str;
public:
const static size_t npos;
};
const size_t string::npos = -1;
ostream& operator<<(ostream& out, const bit::string& s)
{
for (auto e : s)
{
out << e;
}
return out;
}
istream& operator>>(istream & in, bit::string& s)
{
s.clear();
char ch = in.get();
while (ch == ' ' || ch == '\n')
{
ch = in.get();
}
int i = 0;
char buff[128];
while (ch != '\n')
{
buff[i] = ch;
i++;
if (i == 127)
{
s += buff;
buff[i] = '\0';
i = 0;
}
ch = in.get();
}
if (i != 0)
{
buff[i] = '\0';
s += buff;
}
return in;
}
}