#include<iostream>
#include<cstring>
using namespace std;

class String
{
 friend ostream& operator<< (ostream& os,String& s);
public:
 String(const char* str = "") //构造函数
 :_sz(strlen(str))
 ,_capacity(strlen(str)+1)
 ,_str(new char[strlen(str)+1])
 {
 cout<<"String(const char* str)"<<endl;
 strcpy(_str,str);
 }
 String(const String& s) //拷贝构造
 :_sz(s._sz)
 ,_capacity(strlen(s._str)+1)
 ,_str(new char[strlen(s._str)+1])
 {
 cout<<"String(const String& s)"<<endl;
 strcpy(_str,s._str);
 }
 ~String() 
 {
 cout<<"~String()"<<endl;
 if(*_str != NULL)
 {
 delete[] _str;
 _str = NULL;
 _sz = 0;
 _capacity = 0;
 }
 }
 String& operator= (const String& s);
 //String& operator= (const String& s);
 char& operator[] (int index);
 void Push_Back(char c);
 String& operator+= ( const String& str );
 String& operator+= ( const char* s );
 String& operator+= ( char c );
 String& insert ( size_t pos, const String& str );
 String& insert ( size_t pos1, const String& str, size_t pos2, size_t n );
 String& insert ( size_t pos, const char* s, size_t n);
 String& insert ( size_t pos, const char* s );
 String& insert ( size_t pos, size_t n, char c );
private:
 char* _str;
 int _sz;
 int _capacity;
};

String& String::operator= (const String& s)
{
 if(this != &s) //判断两个对象是否相等
 {
 delete[] _str;
 _str = new char[strlen(s._str)+1];
 strcpy(_str,s._str);
 _sz = s._sz;
 _capacity = s._capacity;
 }
 return *this;
}

String& String::operator= (const String& s)
{
 std::swap(_str,s._str);
 return *this;
}

char& String::operator[] (int index)
{
 return _str[index];
}

//由于_str是指向该字符串的指针，_str[ index ]是对下标为index的字符的解引用，所以返回值类型为char

private:
 void CheckCapacity(int count)
 {
 if(_sz+count >= _capacity)
 {
 int newCapacity = 2*_capacity > (_capacity + count) ? 2*_capacity : (_capacity+count);
 char* temp = new char[newCapacity];
 strcpy(temp,_str);
 delete[] _str;
 _str = temp;
 _capacity = newCapacity;
 }
 }

void String::Push_Back(char c)
{
 CheckCapacity(1);
 _str[_sz++] = c;
 _str[_sz] = '\0';
}

 string str1("abcdef");
 string str2("123456");
 str1 += str2;  ------------>>abcdef123456
 str1 += "123456";---------->>abcdef123456
 str1 += 'L';  ----------->>abcdefL

String& String::operator+= ( const String& str )
{
 CheckCapacity(strlen(str._str));
 strcat(_str,str._str);
 _sz += strlen(str._str);
 _str[_sz] = '\0';
 return *this;
}
String& String::operator+= ( const char* s )
{
 CheckCapacity(strlen(s));
 strcat(_str,s);
 _sz += strlen(s);
 _str[_sz] = '\0';
 return *this;
}
String& String::operator+= ( char c )
{
 CheckCapacity(1);
 _str[_sz++] = c;
 _str[_sz] = '\0';
 return *this;
}

string str1("12345");
 string str2("abcde");
 //String& insert ( size_t pos, const String& str );
 str1.insert(3,str2); ------>> 12abcde345
 //String& insert ( size_t pos1, const String& str, size_t pos2, size_t n );
 str1.insert(2,str2,3,2);----->>1cd2345
 //String& insert ( size_t pos, const char* s, size_t n);
 str1.insert(2,"abcdef",3);----->>1abc2345
 //String& insert ( size_t pos, const char* s );
 str1.insert(4,"abc");----->>123abc45
 //String& insert ( size_t pos, size_t n, char c );
 str1.insert(2,5,'c');------>>1ccccc2345
 

String& String::insert ( size_t pos, const String& str )
{
 if((pos>0) && (pos<=strlen(_str))) //判断pos是否合理
 {
 CheckCapacity(strlen(str._str));
 char* tmp = new char[strlen(_str)-pos+2];
 strcpy(tmp,_str+pos-1); //保存_str的pos位及之后的内容
 //我们可以利用strcat函数来追加一个字符串，但前提是必须使前一个字符串（str1）以'\0'结尾
 _str[pos-1] = '\0';
 strcat(_str,str._str);
 strcat(_str,tmp);
 _sz += strlen(str._str);
 _str[_sz] = '\0';
 delete[] tmp;
 }
 return *this;
}
String& String::insert ( size_t pos1, const String& str, size_t pos2, size_t n )
{
 if((pos1>0) && (pos1<=strlen(_str))) //判断pos1是否合理
 {
 if((pos2>0) && (pos2<=strlen(str._str))) //判断pos2是否合理
 {
 if((n>0) && (n<=strlen(str._str)-pos2)) //检测n是否合理
 {
 CheckCapacity(n);
 char* tmp = new char[strlen(_str)-pos1+2];
 strcpy(tmp,_str+pos1-1); //保存_str的pos1位及之后的内容
 _str[pos1-1] = '\0';
 strncat(_str,str._str+pos2-1,n);
 strcat(_str,tmp);
 _sz += strlen(str._str);
 _str[_sz] = '\0';
 delete[] tmp;
 }
 }
 }
 return *this;
}
String& String::insert ( size_t pos, const char* s, size_t n)
{
 if((pos>0) && (pos<=strlen(_str))) //判断pos是否合理
 {
 CheckCapacity(n);
 char* tmp = new char[strlen(_str)-pos+2];
 strcpy(tmp,_str+pos-1); //保存_str的pos位及之后的内容
 _str[pos-1] = '\0';
 strncat(_str,s,n);
 strcat(_str,tmp);
 _sz += strlen(s);
 _str[_sz] = '\0';
 delete[] tmp;
 }
 return *this;
}
String& String::insert ( size_t pos, const char* s )
{
 if((pos>0) && (pos<=strlen(_str))) //判断pos是否合理
 {
 CheckCapacity(strlen(s));
 char* tmp = new char[strlen(_str)-pos+2];
 strcpy(tmp,_str+pos-1); //保存_str的pos位及之后的内容
 _str[pos-1] = '\0';
 strcat(_str,s);
 strcat(_str,tmp);
 _sz += strlen(s);
 _str[_sz] = '\0';
 delete[] tmp;
 }
 return *this;
}
String& String::insert ( size_t pos, size_t n, char c )
{
 if((pos>0) && (pos<=strlen(_str))) //判断pos是否合理
 {
 CheckCapacity(n);
 int i = 1;
 char* tmp = new char[strlen(_str)-pos+2];
 strcpy(tmp,_str+pos-1);//2345
 //_str[pos-1] = '\0';
 for(i=1; i<=n; i++)
 {
 _str[i] = c;
 }
 _str[i] = '\0';
 strcat(_str,tmp);
 _sz += n;
 _str[_sz] = '\0';
 delete[] tmp;
 }
 return *this;
}