string模拟实现
1.构造函数
这里用缺省值,可以让我们把没有初始化的构造省略掉简便代码
string(const char* str="")
{
_capacity = strlen(str);
_size = _capacity;
_str = new char[_capacity + 1];
strcpy(_str, str);
}
2.拷贝构造
拷贝构造就是开一样大的空间,然后把相应的值都赋值进去
string(const string& s)
{
_str = new char[s._capacity + 1];
strcpy(_str, s._str);
_size = s._size;
_capacity = s._capacity;
}
//新版写法
string(const string& s)
{
string tmp(s._str);
swap(tmp);
}
3.赋值运算符重载
赋值和拷贝构造就一点不一样,赋值为了赋值和被赋值的空间大小保持一致,要先开和被赋值一样大的空间,删除原空间
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;
}
//新版写法
string& operator=( string s)
{
swap(s);
return *this;
}
4.析构函数
~string()
{
delete[]_str;
_str = nullptr;
_size = 0;
_capacity = 0;
}
5.reserve
n小于原本的容量,则不改变,reserve的增容的思路非常类似赋值
void reserve(size_t n)
{
if (_capacity < n)
{
char* tmp = new char[n+1];
strcpy(tmp, _str);
delete[]_str;
_str = tmp;
_capacity = n;
}
}
6.字符串访问函数
1.迭代器
typedef char* iterator;
iterator begin()
{
return _str;
}
iterator end()
{
return _str + _size;
}
//const版本
typedef const char* const_iterator;
const_iterator begin()const
{
return _str;
}
const_iterator end()const
{
return _str + _size;
}
2.operator[]
char& operator[](size_t pos)
{
assert(pos <= _size);
return _str[pos];
}
7.增删查改
1.push_back和+=字符
push_back和+=字符本质上一模一样
void push_back(char ch)
{
if (_size == _capacity)
{
size_t newcapacity = 0 ? 4 : _capacity * 2;
reserve(newcapacity);
}
_str[_size] = ch;
_size++;
_str[_size] = '\0';
}
string& operator+=(char ch)
{
push_back(ch);
return *this;
}
2.append和+=字符串
void append(char* str)
{
size_t len = strlen(str);
if (_size + len > _capacity)
{
reserve(_size + len);
}
strcpy(_str + _size, str);
_size += len;
}
string& operator+=(char* str)
{
append(str);
return *this;
}
3.insert
void insert(size_t pos, char ch)
{
if (_size == _capacity)
{
size_t newcapacity = 0 ? 4 : _capacity * 2;
reserve(newcapacity);
}
size_t end = _size;
while (end > (int)pos)
{
_str[end + 1] = _str[end];
end--;
}
_str[pos] = ch;
_size++;
}
void insert(size_t pos, char* str)
{
size_t len = strlen(str);
if (_size + len > _capacity)
{
reserve(_size + len);
}
size_t end = _size;
while (end > (int)pos)
{
_str[end + 1] = _str[end];
end--;
}
strncpy(_str + pos, str, len);
_size += len;
}
4.swap
void swap(string& s)
{
std::swap(_str, s._str);
std::swap(_size, s._size);
std::swap(_capacity, s._capacity);
}
5.erase
如果从pos位置开始向后全部删除那么就直接在pos加\0
void erase(size_t pos, size_t len)
{
if (len = npos || len + pos > _size)
{
_str[pos] = '\0';
_size = pos;
}
else
{
strcpy(_str + pos, _str + pos + len);
_size -= len;
}
}
6.clear
void clear()
{
_size = 0;
_str[0] = '\0';
}
7.find
size_t find(char ch, size_t pos)
{
for (size_t i = pos; i < _size; i++)
{
if (_str[i] == ch)
{
return i;
}
else
{
return npos;
}
}
}
size_t find(char* str, size_t pos)
{
const char* ptr = strstr(_str + pos, str);
if (ptr == nullptr)
{
return npos;
}
else
{
return ptr - _str;
}
}
8.流提取&&流插入
ostream& operator<<(ostream& out, const string& s)
{
for (auto ch : s)
{
out << ch;
}
return out;
}
istream& operator>>(istream& in, string& s)
{
s.clear();
char ch = in.get();
while (ch != ' ' && ch != '\0')
{
s += ch;
ch = in.get();
}
return in;
}
全代码
#pragma once
#include<iostream>
#include<assert.h>
using namespace std;
namespace yjt
{
class string
{
public:
//1.构造函数
string(const char* str="")
{
_capacity = strlen(str);
_size = _capacity;
_str = new char[_capacity + 1];
strcpy(_str, str);
}
//拷贝构造s2(s3)
string(const string& s)
{
_str = new char[s._capacity + 1];
strcpy(_str, s._str);
_size = s._size;
_capacity = s._capacity;
}
//新版写法
string(const string& s)
{
string tmp(s._str);
swap(tmp);
}
//赋值 =
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;
}
//新版写法
string& operator=( string s)
{
swap(s);
return *this;
}
//2.
char* c_str()
{
return _str;
}
//3.
~string()
{
delete[]_str;
_str = nullptr;
_size = 0;
_capacity = 0;
}
//4.
size_t size()
{
return _size;
}
//5.[]
char& operator[](size_t pos)
{
assert(pos <= _size);
return _str[pos];
}
//迭代器
//非const版本
typedef char* iterator;
iterator begin()
{
return _str;
}
iterator end()
{
return _str + _size;
}
//const版本
typedef const char* const_iterator;
const_iterator begin()const
{
return _str;
}
const_iterator end()const
{
return _str + _size;
}
//6.
void reserve(size_t n)
{
if (_capacity < n)
{
char* tmp = new char[n+1];
strcpy(tmp, _str);
delete[]_str;
_str = tmp;
_capacity = n;
}
}
//7.
void push_back(char ch)
{
if (_size == _capacity)
{
size_t newcapacity = 0 ? 4 : _capacity * 2;
reserve(newcapacity);
}
_str[_size] = ch;
_size++;
_str[_size] = '\0';
}
void append(char* str)
{
size_t len = strlen(str);
if (_size + len > _capacity)
{
reserve(_size + len);
}
strcpy(_str + _size, str);
_size += len;
}
string& operator+=(char ch)
{
push_back(ch);
return *this;
}
string& operator+=(char* str)
{
append(str);
return *this;
}
//8
void insert(size_t pos, char ch)
{
if (_size == _capacity)
{
size_t newcapacity = 0 ? 4 : _capacity * 2;
reserve(newcapacity);
}
size_t end = _size;
while (end > (int)pos)
{
_str[end + 1] = _str[end];
end--;
}
_str[pos] = ch;
_size++;
}
void insert(size_t pos, char* str)
{
size_t len = strlen(str);
if (_size + len > _capacity)
{
reserve(_size + len);
}
size_t end = _size;
while (end > (int)pos)
{
_str[end + 1] = _str[end];
end--;
}
strncpy(_str + pos, str, len);
_size += len;
}
//9
void erase(size_t pos, size_t len)
{
if (len = npos || len + pos > _size)
{
_str[pos] = '\0';
_size = pos;
}
else
{
strcpy(_str + pos, _str + pos + len);
_size -= len;
}
}
//10
size_t find(char ch, size_t pos)
{
for (size_t i = pos; i < _size; i++)
{
if (_str[i] == ch)
{
return i;
}
else
{
return npos;
}
}
}
size_t find(char* str, size_t pos)
{
const char* ptr = strstr(_str + pos, str);
if (ptr == nullptr)
{
return npos;
}
else
{
return ptr - _str;
}
}
void swap(string& s)
{
std::swap(_str, s._str);
std::swap(_size, s._size);
std::swap(_capacity, s._capacity);
}
void clear()
{
_size = 0;
_str[0] = '\0';
}
private:
char* _str;
size_t _size;
size_t _capacity;
static const size_t npos = -1;
};
ostream& operator<<(ostream& out, const string& s)
{
for (auto ch : s)
{
out << ch;
}
return out;
}
istream& operator>>(istream& in, string& s)
{
s.clear();
char ch = in.get();
while (ch != ' ' && ch != '\0')
{
s += ch;
ch = in.get();
}
return in;
}
void text1()
{
string s1("hello world");
cout << s1.c_str() << endl;
string s2;
cout << s2.c_str() << endl;
string::iterator it = s1.begin();
while (it != s1.end())
{
cout << *it << " ";
it++;
}
cout << endl;
for (auto e : s1)
{
cout << e << " ";
}
cout << endl;
}
void text2()
{
string s1("hello world");
cout << s1.c_str() << endl;
//string s2(s1);
string s2 = s1;
cout << s2.c_str() << endl;
}
}