12-0.cpp

Accelerated C++ 课后练习题 本人自己完成、可供参考

#include<iostream>
#include<memory> 
#include<iterator>
#include<string>
#include<fstream>
using std::string;
using std::cout;
using std::endl;
using std::cin;
using std::allocator;
using std::_MAX;
using std::uninitialized_copy;
using std::uninitialized_fill;
using std::istream;
using std::ostream;
using std::ifstream;
using std::ofstream;

template <class T> class Vec
{
public:
	typedef T* iterator;
	typedef const T* const_iterator;
	typedef size_t size_type;
	typedef T value_type;

	Vec() { create(); }
	explicit Vec(size_type n,const T& t=T()) { create(n,t);}
	
	Vec(const Vec& v) { create(v.begin(),v.end()); }
	Vec& operator=(const Vec&);
	~Vec() { uncreate();}

	T& operator[](size_type i) { return data[i]; }
	const T& operator[](size_type i) const {return data[i];}

	void push_back(const T& t)
	{
		if(avail==limit)
			grow();
		unchecked_append(t);
	}

	iterator erase(iterator);
	void clear();

	size_type size() const {return avail-data;}

	iterator begin() { return data;}
	const_iterator begin() const { return data;}

	iterator end() { return avail;}
	const_iterator end() const { return avail; }
private:
	iterator data;		//first element in the Vec
	iterator avail;		//(one past) the last of element in the Vec
	iterator limit;		//(one past) the allocated menory

	//facilities for memory allocation
	allocator<T> alloc;	//object to handle memory allocation
	
	//allocation and initialize the underlying array
	void create();
	void create(size_type,const T&);
	void create(const_iterator, const_iterator);

	//destroy the element in the array and free the memory
	void uncreate();

	//support funcions for push_back
	void grow();
	void unchecked_append(const T&);

};

template<class T>
Vec<T>& Vec<T>::operator =(const Vec& rhs)
{
	//check for self-assignment
	if(&rhs!=this)
	{
		//free the array in the left-hand side
		uncreate();
		//copy elements from the right-hand to the left-hand side
		create(rhs.begin(),rhs.end());
	}
	return *this;
}
template <class T> void Vec<T>::create()
{
	data=avail=limit=0;
}
template <class T> void Vec<T>::create(size_type n, const T& val)
{
	data=alloc.allocate(n,0);
	limit=avail=data+n;
	uninitialized_fill(data,limit,val);
}
template <class T> 
void Vec<T>::create(const_iterator i,const_iterator j)
{
	data=alloc.allocate(j-i,0);
	limit=avail=uninitialized_copy(i,j,data);
}
template <class T> void Vec<T>::uncreate()
{
	if(data)
	{
		//destroy (in reverse orde) the elements that were constructed
		iterator it=avail;
		while(it!=data)
			alloc.destroy(--it);

		//return all the space that was allocated
		alloc.deallocate(data,limit-data);
	}
	//reset pointers to indicate that the Vec is empty again
	data=limit=avail=0;
}
template <class T> void Vec<T>::grow()
{
	//when growing, allocate twice as much space as currently in use
	size_type new_size=_MAX(2*(limit-data),ptrdiff_t(1));

	//allocate new space and copy existing elements to the new space
	iterator new_data=alloc.allocate(new_size,0);
	iterator new_avail=uninitialized_copy(data,avail,new_data);

	//return the old space
	uncreate();

	//reset pointers to point to the newly allocate space
	data=new_data;
	avail=new_avail;
	limit=data+new_size;
}
template <class T> void Vec<T>::unchecked_append(const T& val)
{
	alloc.construct(avail++,val);
}
template <class T> Vec<T>::iterator Vec<T>::erase(iterator i)
{
	std::copy(i+1,avail,i);
	--avail;
	return i;
}
template <class T> void Vec<T>::clear()
{
	uncreate();
}



class Str
{
	//input operator 
	 friend istream& operator>>(istream&, Str&);

public:
	Str& operator+=(const Str& s)
	{
		std::copy(s.data.begin(),s.data.end(),std::back_inserter(data));
		return *this;
	}

	typedef Vec<char>::size_type size_type;
	
	//default constructor ;create an empty Str
	Str(){}

	//create a Str containing  n copies c
	Str(size_type n,char c):data(n,c){}

	//create s Str from a null-teminated array of char
	Str(const char* cp)
	{
		std::copy(cp,cp+strlen(cp),std::back_inserter(data));
	}

	//create a Str from the rang denoted by iterators b and e
	template<class In> Str(In b,In e)
	{
		std::copy(b,e,std::back_inserter(data));
	}

	char& operator[](size_type i){return data[i];}
	const char& operator[](size_type i) const {return data[i];}

	size_type size() const{return data.size();}
	
	const char* c_str() const;
	const char* c_date() const;
	const char* copy(char*,size_type) const;
private:
	Vec<char> data;
};
const char* Str::copy(char* p,size_type n) const
{
	if(strlen(p)<n)
		throw "benefit!";
	else
	{
		std::copy(data.begin(),data.begin()+n,p);
		return p;
	}
}
const char* Str::c_str() const
{
	char* p=new char[size()];
	std::copy(data.begin(),data.end(),p);
	p[size()]=0;
	return p;
}
const char* Str::c_date() const
{
	char* p=new char[size()-1];
	std::copy(data.begin(),data.end(),p);
	return p;
}
ostream& operator<<(ostream& os, const Str& s)
{
	for(Str::size_type i=0;i<s.size();++i)
		os<<s[i];
	return os;
}

istream& operator>>(istream& is, Str& s)
{
	//obliterate existing value (s)
	s.data.clear();

	//read and discard leading whitespace
	char c;
	while(is.get(c)&&isspace(c))
		;//nothing to do, except testing the condition

	//if still something to read, do so until next whitespace charactor
	if(is)
	{
		do
			s.data.push_back(c);	//compile error! data is private
		while(is.get(c)&&!isspace(c));

		//if we read whitespace, then put it back on the stream
		if(is)
			is.unget();
	}
	return is;
}

Str operator+(const Str& s,const Str& t)
{
	Str r=s;
	r+=t;
	return r;
}

int main()
{
	Str ch="cheng";
	string s;
	ifstream infile(ch.c_str());
	std::getline(infile,s);
	cout<<s<<endl;

	return 0;
}