先是了解string各个函数的用法及参数
#include<iostream>
#include"string"
//#include"String.h"
//#include"string.cpp"
using namespace std;
void String()
{
string s1;
string s2("hello");
string s3(5, 'a');
string s4(s2);
string s5(s2, 1);
cout << s2 << endl;
cout << s2.capacity() << endl;
s1 += "sttr";
cout << s1 << endl;
}
void String1()
{
string str;
str.push_back(' ');
str.append("hello");
str += 'b';
str += "it"; //追加字符串
cout << str << endl;
cout << str.c_str() << endl; // 以C语言的方式打印字符串
// 获取file的后缀
string file1("string.cpp");
size_t pos = file1.rfind('.');
string suffix(file1.substr(pos, file1.size() - pos));
cout << suffix << endl;
string url("http://www.cplusplus.com/reference/string/string/find/");
cout << url << endl;
size_t start = url.find("://");
if (start == string::npos)
{
cout << "invalid url" << endl;
return;
}
start += 3;
size_t finish = url.find('/', start);
string address = url.substr(start, finish - start);
cout << address << endl;
// 删除url的协议前缀
pos = url.find("://");
url.erase(0, pos + 3);
cout << url << endl;
}
int main()
{
String1();
}注意：调用string时头文件一定引入并且一定要有using naemspace std;
接下来是string的模拟实现：
下面是头文件（.h）
#pragma once
#include<iostream>
#include<assert.h>
using namespace std;
namespace bit
{
class String
{
public:
typedef char* iterator;
typedef const char* iterator;
iterator begin()
{
return _str;
}
iterator end()
{
return _str + _size;
}
String(const char* str="")
{
_size = strlen(str);
_capacity = _size > 15 ? _size : 15;
_str = new char[_capacity + 1];
strcpy(_str, str);
}
~String()
{
delete[] _str;
_str = nullptr;
_size = _capacity = 0;
}
String(const String&s)
:_str(nullptr)
, _size(0)
, _capacity(0)
{
String tmp(s._str);
this->Swap(tmp);
}
String& operator=(String s)
{
this->Swap(s);
return *this;
}//s1 = s2
char& operator[](size_t pos)
{
assert(pos < _size);
return _str[pos];
}
char& operator[](size_t pos)const
{
assert(pos < _size);
return _str[pos];
}
size_t Size() const
{
return _size;
}
size_t capacity()const
{
return _capacity;
}
const char* c_str()
{
return _str;
}
void Reserve(size_t n);
void Resize(size_t n, char ch = '\0');
void PushBack(char ch);
void Append(const char* str);
String& operator+=(char ch);
String& operator+=(const char* str);
size_t Find(char ch, size_t pos = 0);
size_t RFind(char ch, size_t pos = npos);
size_t Find(const char* str, size_t pos = 0);
void Insert(size_t pos, char ch);
void Insert(size_t pos, const char* str);
void Erase(size_t pos, size_t len = npos);
String Substr(size_t pos, size_t len = npos);
void Swap(String& s)
{
swap(_str, s._str);
swap(_size, s._size);
swap(_capacity, s._capacity);
}
private:
char* _str;
size_t _size;
size_t _capacity;
public:
static const size_t npos;
};
}之后就是各个函数的实现（.cpp）
using bit::String;
const size_t String::npos = -1;
void String::Reserve(size_t n)
{
if (n > _capacity)
{
char* new_str = new char[n + 1];
strcpy(new_str, _str);
delete[] _str;
_str = new_str;
_capacity = n;
}
}
void String::Resize(size_t n, char ch = '\0')
{
if (n <= _size)
{
_str[n] = '/0';
_size = n;
}
else
{
if (n > _capacity)
{
Resize(n);
}
size_t pos = _size;
while (pos < n)
{
_str[pos] = ch;
++pos;
}
_size = n;
_str[n] = '/0';
}
}
void String::PushBack(char ch)
{
/*if (_size == _capacity)
{
Resize(1.5*_capacity);
}
_str[_size] = ch;
_size++;
_str[_size] = '/0';*/
Insert(_size,ch);
}
void String::Append(const char* str)
{
/*size_t len = strlen(str);
if (len + _size > _capacity)
{
Resize(len + _size);
}
strcpy(_str + _size, str);
_size += len;*/
Insert(_size, str);
}
String& String::operator+=(char ch)
{
this->PushBack;
return *this;
}
String& String::operator+=(const char* str)
{
this->Append;
return *this;
}
size_t String::Find(char ch, size_t pos = 0)
{
assert(pos < _size);
while (pos < _size)
{
if (_str[pos] = ch)
{
return pos;
}
pos++;
}
return String::npos;
}
size_t String::RFind(char ch, size_t pos = npos)
{
int end = _size - 1;
if (pos != String::npos)
{
assert(pos < _size);
end = pos;
}
while (end >= 0)
{
if (_str[end] = ch)
{
return end;
}
end--;
}
return String::npos;
}
size_t String::Find(const char* str, size_t pos )
{
assert(pos < _size);
char* p = strstr(_str + pos, str);
if (p == nullptr)
{
return String::npos;
}
else
{
return p - _str;
}
}
String String::Substr(size_t pos, size_t len)
{
if (_size - pos < len)
{
len = _size - pos;
}
String sub;
sub.Reserve(len);
for (size_t i = pos; i < pos + len; ++i)
{
sub += _str[i];
}
return sub;
}
void String::Insert(size_t pos, char ch)
{
assert(_size > pos);
if (_size == _capacity)
{
Reserve(1.5*_capacity);
}
int end = _size;
while (end >= (int)pos)
{
_str[end + 1] = _str[end];
--end;
}
_str[end] = ch;
_size++;
}
void String::Insert(size_t pos, const char* str)
{
assert(_size > pos);
size_t len = strlen(str);
if (_size = _capacity)
{
Reserve(1.5*(_size + len));
}
int end = _size;
while (end > (int)pos)
{
_str[end + len] = _str[end];
--end;
}
while (*str)
{
_str[pos++] = *str++;
}
_size += len;
}
void String::Erase(size_t pos, size_t len)
{
assert(pos < _size);
if (pos == npos || pos + len > _size)
{
_str[pos] = '/0';
_size = pos;
}
else
{
for (int i = 0; i < len; i++)
{
_str[pos] = _str[pos + len];
pos++;
}
_size -=len;
_str[_size] = '/0';
}
}