引子：我们学习了c++中的string类，那我们能不能像以前数据结构一样自己实现string类呢？以下是cplusplus下的string类，我们参考参考！
废话不多说，直接代码实现：（注意函数之间的复用！）
#define _CRT_SECURE_NO_WARNINGS 1
#pragma once
#include<iostream>
#include<assert.h>
using namespace std;
//一般在类外进行静态区变量赋值
const static size_t npos = -1;
//本string简单实现，代码量小，故直接写在声明中
namespace bit
{
class string
{
public:
//采用typedef 让iterator保持接口的一致性
//iterator底层是模版template
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;
}
//构造函数
string(const char* str = "")
:_size(strlen(str))
{
_str = new char[_size + 1];//为深拷贝，因为如果浅拷贝的话，共用一块空间，那结果可想而知
_capacity = _size;
strcpy(_str, str);//注意char * strcpy ( char * destination, const char * source );
}
//拷贝构造,可以隐式类型赋值
string(const string& s)
{
_str = new char[s._capacity + 1];
strcpy(_str, s._str);
_size = s._size;
_capacity = s._capacity;
}
string& operator=(const string& s)
{
if (this != &s)//排除等于自身的情况
{
char* tmp = new char[s._capacity + 1];
strcpy(tmp, s._str);
delete[]_str;//只析构_str上的资源
_str = tmp;
_size = s._size;
_capacity = s._capacity;
}
return *this;
}
~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)
{
if (n > _capacity)
{
char* tmp = new char[n + 1];
strcpy(tmp, _str);
delete[] _str;
_str = tmp;
_capacity = n;
}
}
void insert(size_t pos, char ch)
{
assert(pos <= _size);
if (_size == _capacity)
{
size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;
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);
size_t len = strlen(str);
if (_size + len > _capacity)
{
reserve(_size + len);
}
size_t end = _size;
//注意pos=0时，对应的值为size_t类型，要int转
while (end > (int)pos)
{
_str[end+len] = _str[end];
--end;
}
memcpy(_str + pos, str, len);//void * memcpy ( void * destination, const void * source, size_t num );
_size += len;
}
void push_back(char ch)
{
insert(_size, ch);
}
void append(const char* str)
{
insert(_size, str);
}
string& operator+=(char ch)
{
push_back(ch);
return *this;
}
string& operator+=(const char* str)
{
append(str);
return *this;
}
void erase(size_t pos = 0, size_t len = npos)
{
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 find(char ch, size_t pos = 0)
{
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* p = strstr(_str + pos, str);//char * strstr (char * str1, const char * str2 );
return p - _str;
}
void swap(string& s)
{
std::swap(_str, s._str);
std::swap(_size, s._size);
std::swap(_capacity, s._capacity);
}
string substr(size_t pos = 0, size_t len = npos)
{
// 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 operator<(const string& s) const
{
return strcmp(_str, s._str) < 0;
}
bool operator>(const string& s) const
{
return !(*this <= s);
}
bool operator<=(const string& s) const
{
return *this < s || *this == s;
}
bool operator>=(const string& s) const
{
return !(*this < s);
}
bool operator==(const string& s) const
{
return strcmp(_str, s._str) == 0;
}
bool operator!=(const string& s) const
{
return !(*this == s);
}
void clear()
{
_str[0] = '\0';
_size = 0;
}
private:
// char _buff[16];
char* _str;
size_t _size;
size_t _capacity;
const static size_t npos;
};
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;
}
}
长图形式：
![char x[]---char*---string---sizeof](https://img-blog.csdnimg.cn/direct/58cc3f260525498d9a0704c0513ffdac.png)
