String的写时拷贝
#pragma once
#include <iostream>
#include <string.h>
#include <cstdio>
#include <assert.h>
using namespace std;
#define TESTHEADER printf("\n================%s=============\n", __FUNCTION__)
class String
{
public:
String(const char* str);
String(const String& s);
String& operator = (const String s);
~String();
char* c_str();
void CopyOnWrite();
char& operator [] (size_t pos);
const char& operator [] (size_t pos)const;
String& Insert(size_t pos, char ch);
String& Insert(size_t pos, const char* str);
String& Append(const char* str);
String& Erase(size_t pos, size_t n);
void Expand(size_t n);
private:
char* _str;
int* _pcount;
size_t _size;
size_t _capacity;
};
#include "test.h"
String::String(const char* str)
:_size(strlen(str))
,_capacity(_size)
{
_str = new char [strlen(str) + 1];
_pcount = new int(1);
strcpy(_str, str);
}
String::String(const String& s)
{
_str = s._str;
_pcount = s._pcount;
++(*_pcount);
_size = s._size;
_capacity = s._capacity;
}
String& String:: operator = (const String s)
{
if(_str != s._str)
{
_str = s._str;
--(*_pcount);
if(*_pcount == 0)
{
delete [] _str;
delete _pcount;
}
_size = s._size;
_capacity = s._capacity;
}
return *this;
}
String::~String()
{
delete [] _str;
delete _pcount;
_size = 0;
_capacity = 0;
}
char* String::c_str()
{
return _str;
}
void String::CopyOnWrite()
{
if(*_pcount > 1)
{
char* tmp = new char[_size + 1];
strcpy(tmp, _str);
--(*_pcount);
_str = tmp;
_pcount = new int(1);
}
}
char& String::operator [] (size_t pos)
{
CopyOnWrite();
return _str[pos];
}
const char& String:: operator [] (size_t pos)const
{
return _str[pos];
}
void String::Expand(size_t n)
{
if( *_pcount == 1)
{
char* tmp = new char [n];
strcpy(tmp, _str);
delete [] _str;
--(*_pcount);
delete _pcount;
_pcount = new int(1);
_str = tmp;
}
else
{
char* tmp = new char [n];
strcpy(tmp, _str);
_str = tmp;
--(*_pcount);
_pcount = new int(1);
}
}
String& String::Insert(size_t pos, char ch)
{
assert(pos < _size);
if(_size == _capacity)
{
Expand(2 * _capacity);
}
int end = _size;
for(; end >= (int)pos; end--)
{
_str[end] = _str[end - 1];
}
_str[pos] = ch;
return *this;
}
String& String::Insert(size_t pos, const char* str)
{
assert(pos <= _size);
int len = strlen(str);
if(_size == _capacity)
{
Expand(_size + len);
}
int end = _size;
for(; end >= (int)pos; end--)
{
_str[end + len] = _str[end];
}
strncpy(_str + pos, str, len);
_size += len;
return *this;
}
String& String::Append(const char* str)
{
int len_ = strlen(_str);
int len = strlen(str);
if(_size == _capacity)
{
Expand(_size + len);
}
strcpy(_str + len_, str);
_size += len;
return *this;
}
String& String::Erase(size_t pos, size_t n)
{
assert(pos <= _size);
CopyOnWrite();
if(pos + _size > _capacity)
{
_str[pos] = '\0';
}
strcpy(_str + pos, _str + pos + n);
_size -= n;
return *this;
}