一、模拟实现构造函数、析构函数
class string
{
public:
string(const char* str="")
:_size(strlen(str))
,_capacity(_size)
{
_str = new char[_capacity + 1];
strcpy(_str, str);
}
~string()
{
delete[] _str;
_str = nullptr;
_size = _capacity = 0;
}
}
二、实现扩容
void reserve(size_t n)
{
if (n > _capacity)
{
char* tmp = new char[n + 1];//多一个留\0
strcpy(tmp, _str); //strcpy会把\0也拷贝过去
delete[] _str;
_str = tmp;
_capacity = n;
}
}三、模拟实现插入
1.push_back
void push_back(char ch)//插入字符
{
if (_size== _capacity)
{
reserve(_capacity==0?4:_capacity*2);
}
_str[_size] = ch;
++_size;
_str[_size] = '\0';
}2.append
//5 20
void append(const char* str)//插入字符串
{
size_t len = strlen(str);
if (_size + len > _capacity)
{
reserve(_size + len);
}
}3.+=
string& operator+=(char ch)
{
push_back(ch);
return *this;
}
string& operator+=(const char* str)
{
append(str);
return *this;
}4.insert
void insert(size_t pos, char ch)//在pos位置插入一个字符
{
assert(pos <= _size);
if (_size == _capacity)
{
reserve(_capacity == 0 ? 4 : _capacity * 2);
}
int end = _size;
while (end >=(int) pos)
{
_str[end + 1] = _str[end];
--end;
}
_str[pos] = ch;
_size++;
}
头插存在问题，循环在end<pos才会结束，pos最小是0，size_t无符号整形，最小是0，所以会崩溃，解决方案一：把pos转为int
void insert(size_t pos, char ch)//在pos位置插入一个字符
{
assert(pos <= _size);
if (_size == _capacity)
{
reserve(_capacity == 0 ? 4 : _capacity * 2);
}
size_t end = _size+1;
while (end >pos)
{
_str[end] = _str[end-1];
--end;
}
_str[pos] = ch;
_size++;
}四、运算符重载
> < == >= <= !=
//s1<s2
bool operator<(const string& s) const//只要不修改
{
return strcmp(_str,s._str) < 0;
}
bool operator==(const string& s) const
{
return strcmp(_str,s._str) == 0;
}
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 !(*this < s);
}
bool operator!=(const string& s) const
{
return !(*this == s);
}五、流插入和流提取
1.流插入
ostream& operator<<(ostream& out, const string& s)//用友元是因为我们想访问私有，但是我们通过公有的成员函数就可以访问就不需要友元
{
for (size_t i = 0; i < s.size(); i++)
{
out << s[i];
}
return out;
}2.流提取
istream& operator>>(istream& in, string& s)//流提取是要从缓冲区中取字符
{
s.clear();
char ch;
//in >> ch;//拿不到空格
ch = in.get();//一个字符一个字符的拿，可以拿到空格
while (ch != ' ' && ch != '\n')//遇到空格或者换行默认结束
{
s += ch;
//in >> ch;
ch = in.get();
}
return in;
}相比较于C语言的scanf的优势是什么？
不需要提前开空间，空间不够会扩容，+=，不管你输入多少字符串，只要你内存够，都可以搞定
#pragma once
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//内容不可以修改
{
return _str;
}
const_iterator end() const
{
return _str + _size;
}
string(const char* str="")
:_size(strlen(str))
,_capacity(_size)
{
_str = new char[_capacity + 1];
strcpy(_str, str);
}
char& operator[](size_t pos)
{
assert(pos < _size);
return _str[pos];
}
const char& operator[](size_t pos) const //可以读不能写
{
assert(pos < _size);
return _str[pos];
}
void reserve(size_t n)
{
if (n > _capacity)
{
char* tmp = new char[n + 1];//多一个留\0
strcpy(tmp, _str); //strcpy会把\0也拷贝过去
delete[] _str;
_str = tmp;
_capacity = n;
}
}
void push_back(char ch)//插入字符
{
if (_size== _capacity)
{
reserve(_capacity == 0 ? 4 : _capacity * 2);
}
_str[_size] = ch;
++_size;
_str[_size] = '\0';
}
//5 20
void append(const char* str)//插入字符串
{
size_t len = strlen(str);
if (_size + len > _capacity)
{
reserve(_size + len);
}
}
string& operator+=(char ch)
{
push_back(ch);
return *this;
}
string& operator+=(const char* str)
{
append(str);
return *this;
}
void insert(size_t pos, char ch)//在pos位置插入一个字符
{
assert(pos <= _size);
if (_size == _capacity)
{
reserve(_capacity == 0 ? 4 : _capacity * 2);
}
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)//在pos位置插入一个字符串
{
assert(pos <= _size);
if (_size == _capacity)
{
reserve(_capacity == 0 ? 4 : _capacity * 2);
}
size_t end = _size + 1;
size_t len = strlen(str);
while (end > pos)
{
_str[end+len-1] = _str[end - 1];
--end;
}
for (size_t i = 0; i < len; i++)
{
_str[pos++] = str[i];
}
_size++;
}
void erase(size_t pos, size_t len = npos)
{
}
//s1<s2
bool operator<(const string& s) const//只要不修改
{
return strcmp(_str,s._str) < 0;
}
bool operator==(const string& s) const
{
return strcmp(_str,s._str) == 0;
}
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 !(*this < s);
}
bool operator!=(const string& s) const
{
return !(*this == s);
}
size_t capacity() const
{
return _capacity;
}
size_t size() const
{
return _size;
}
~string()
{
delete[] _str;
_str = nullptr;
_size = _capacity = 0;
}
const char* c_str()
{
return _str;
}
void clear()
{
_str[0] = '\0';
_size = 0;
}
private:
char* _str;
size_t _size;
size_t _capacity;
const static size_t npos;//静态成员变量不属于对象，必须类外初始化，只有const静态整形可以
};
const size_t string::npos = -1;
ostream& operator<<(ostream& out, const string& s)//用友元是因为我们想访问私有，但是我们通过公有的成员函数就可以访问就不需要友元
{
for (size_t i = 0; i < s.size(); i++)
{
out << s[i];
}
return out;
}
istream& operator>>(istream& in, string& s)//流提取是要从缓冲区中取字符
{
s.clear();
char ch;
//in >> ch;//拿不到空格
ch = in.get();//一个字符一个字符的拿，可以拿到空格
while (ch != ' ' && ch != '\n')//遇到空格或者换行默认结束
{
s += ch;
//in >> ch;
ch = in.get();
}
return in;
}
void test_string1()
{
/*string s2;
cout << s2.c_str() << endl;
for (size_t i = 0; i < s1.size(); i++)
{
cout << s1[i] << " ";
}
cout << endl;
string::iterator it = s1.begin();
while (it != s1.end())
{
cout << *it << " ";
++it;
}
cout << endl;
for (auto ch : s1)
{
cout << ch << " ";
}
cout << endl;*/
string s1("hello world");
cout << s1.c_str() << endl;
const char* str = "str";
s1.insert(10, str);
cout << s1.c_str() << endl;
}
}