Essential C++ 第五章代码

版本一(5.1~5.6内容)

#include <iostream>
#include <vector>

using namespace std;

class num_sequence{
public:
virtual ~num_sequence() {};

virtual int elem(int pos) const = 0;
virtual const char* what_am_i() const = 0;
static int max_elem() { return _max_elems;}
virtual ostream& print(ostream &os = cout ) const = 0;

protected:
virtual void gen_elems(int pos) const = 0;
bool check_integrity(int pos, int size) const;

const static int _max_elems = 25;

};

bool num_sequence::check_integrity(int pos,int size) const
{
if (pos <= 0 || pos >= _max_elems)
{
cerr << "!! invalid position: " << pos
<< " Cannot honor request.\n";
return false;
}

if (pos > size)
gen_elems(pos);

return true;
}

ostream& operator<<( ostream &os, const num_sequence &ns)
{
return ns.print( os);
}

class Fibonacci:public num_sequence{
public:
Fibonacci( int len = 1, int beg_pos = 1)
: _length(len), _beg_pos(beg_pos) {}

virtual int elem(int pos) const;
virtual const char* what_am_i() const { return "Fibonacci";}
virtual ostream& print( ostream &os = cout) const;
int length() const { return _length;}
int beg_pos() const { return _beg_pos;}

protected:
virtual void gen_elems(int pos) const;
int _length;
int _beg_pos;
static vector<int> _elems;
};

vector<int>  Fibonacci::_elems;

int Fibonacci::elem(int pos) const
{
if (! check_integrity(pos,_elems.size()))
return 0;

return _elems[pos-1];
}

void Fibonacci::gen_elems(int pos) const
{
if (_elems.empty())
{
_elems.push_back(1);
cout << "gen_elems: 1\n";
_elems.push_back(1);
cout << "gen_elems: 1\n";
}

if (_elems.size() <= (unsigned)pos)
{
int ix = _elems.size();
int n_2 = _elems[ix-2];
int n_1 = _elems[ix-1];

for(; ix < pos; ++ix)
{
int elem = n_2 + n_1;
cout << "gen_elems: " <<elem << endl;
_elems.push_back(elem);
n_2 = n_1;
n_1 = elem;

}
}
}

ostream& Fibonacci::print(ostream &os) const
{
int elem_pos = _beg_pos - 1;
int end_pos = elem_pos + _length;

if ( (unsigned)end_pos > _elems.size() )
Fibonacci::gen_elems(end_pos);

while (elem_pos < end_pos)
os << _elems[elem_pos++] << ' ';

return os;
}

class Triangular:public num_sequence{
public:
Triangular( int len = 1, int beg_pos = 1)
: _length(len), _beg_pos(beg_pos) {}

virtual int elem(int pos) const;
virtual const char* what_am_i() const { return "Triangular";}
virtual ostream& print( ostream &os = cout) const;
int length() const { return _length;}
int beg_pos() const { return _beg_pos;}

protected:
virtual void gen_elems(int pos) const;
int _length;
int _beg_pos;
static vector<int> _elems;
};

vector<int>  Triangular::_elems;

int Triangular::elem(int pos) const
{
if (! check_integrity(pos,_elems.size()))
return 0;

return _elems[pos-1];
}

void Triangular::gen_elems(int pos) const
{
if (_elems.size() <= (unsigned)pos)
{
int ix = _elems.size() ? _elems.size()+1 : 1;
for( ; ix <= pos; ++ix)
{
_elems.push_back(ix*(ix+1)/2);
cout << "gen_elems: " << *(--_elems.end()) << endl;
}

}

}

ostream& Triangular::print(ostream &os) const
{
int elem_pos = _beg_pos - 1;
int end_pos = elem_pos + _length;

if ( (unsigned)end_pos > _elems.size() )
Triangular::gen_elems(end_pos);

while (elem_pos < end_pos)
os << _elems[elem_pos++] << ' ';

return os;
}

inline void display(const num_sequence &ns, int pos, ostream &os = cout)
{
os << "The element at position " << pos
<< " for the " << ns.what_am_i() << " sequence is "
<< ns.elem(pos) << endl;
}

int main()
{
Fibonacci fib;
cout << fib << endl << endl;
Fibonacci fib2(6);
cout << fib2 << endl << endl;
Fibonacci fib3(5,8);
cout << fib3 << endl;
cout << fib3.elem(20) << endl;
Triangular tri(2,5);
cout << tri << endl;

display(tri,20);

}

版本二(5.7~5.10)

#include <iostream>
#include <vector>
#include <typeinfo>

using namespace std;

class num_sequence{
public:
virtual ~num_sequence() {};

//    virtual const char* what_am_i() const = 0;

int elem(int pos) const;
int length() const { return _length;}
int beg_pos() const { return _beg_pos;}

static int max_elem() { return _max_elems;}

ostream& print(ostream &os = cout ) const;

inline const char* what_am_i() const { return typeid(*this).name();}

protected:
//    virtual void gen_elems(int pos) const = 0;
bool check_integrity(int pos, int size) const;

virtual void gen_elems(int pos) const = 0;

const static int _max_elems = 25;

num_sequence(int len, int bp, vector<int> &re )
: _length(len), _beg_pos(bp), _relems(re) {}

int _length;
int _beg_pos;
vector<int> &_relems;

};

bool num_sequence::check_integrity(int pos,int size) const
{
if (pos <= 0 || pos >= _max_elems)
{
cerr << "!! invalid position: " << pos
<< " Cannot honor request.\n";
return false;
}

if (pos > size)
gen_elems(pos);

return true;
}

int num_sequence::elem(int pos) const
{
if (! check_integrity(pos,_relems.size()))
return 0;

return _relems[pos-1];
}

ostream& num_sequence::print(ostream &os) const
{
int elem_pos = _beg_pos - 1;
int end_pos = elem_pos + _length;

if ( (unsigned)end_pos > _relems.size() )
gen_elems(end_pos);

os << what_am_i() << " (" << length() << "," << beg_pos() << "): " ;

while (elem_pos < end_pos)
os << _relems[elem_pos++] << ' ';

return os;
}

class Fibonacci:public num_sequence{
public:
Fibonacci( int len = 1, int beg_pos = 1)
: num_sequence(len, beg_pos, _elems) {}

//    virtual const char* what_am_i() const { return "Fibonacci";}

protected:
virtual void gen_elems(int pos) const;
static vector<int> _elems;
};

vector<int>  Fibonacci::_elems;

void Fibonacci::gen_elems(int pos) const
{
if (_elems.empty())
{
_elems.push_back(1);
//        cout << "gen_elems: 1\n";
_elems.push_back(1);
//        cout << "gen_elems: 1\n";
}

if (_elems.size() <= (unsigned)pos)
{
int ix = _elems.size();
int n_2 = _elems[ix-2];
int n_1 = _elems[ix-1];

for(; ix < pos; ++ix)
{
int elem = n_2 + n_1;
//            cout << "gen_elems: " <<elem << endl;
_elems.push_back(elem);
n_2 = n_1;
n_1 = elem;

}
}
}

class Triangular:public num_sequence{
public:
Triangular( int len = 1, int beg_pos = 1)
: num_sequence(len, beg_pos, _elems) {}

//    virtual const char* what_am_i() const { return "Triangular";}

protected:
virtual void gen_elems(int pos) const;
static vector<int> _elems;
};

vector<int>  Triangular::_elems;

void Triangular::gen_elems(int pos) const
{
if (_elems.size() <= (unsigned)pos)
{
int ix = _elems.size() ? _elems.size()+1 : 1;
for( ; ix <= pos; ++ix)
{
_elems.push_back(ix*(ix+1)/2);
//            cout << "gen_elems: " << *(--_elems.end()) << endl;
}

}
}

ostream& operator<<( ostream &os, const num_sequence &ns)
{
return ns.print( os);
}

inline void display(const num_sequence &ns, int pos, ostream &os = cout)
{
os << "The element at position " << pos
<< " for the " << ns.what_am_i() << " sequence is "
<< ns.elem(pos) << endl;
}

int main()
{
Fibonacci fib;
cout << fib << endl;
Fibonacci fib2(6);
cout << fib2 << endl;
Fibonacci fib3(5,8);
cout << fib3 << endl;
Fibonacci fib4(fib3);
Fibonacci fib5 = fib4;
cout << fib5 << endl;

Triangular tri(2,5);
cout << tri << endl;
display(tri,20);
}

版本二中,return typeid(*this).name(),会分别返回"9Fibonacci","10Triangular",前面的数字表示的是后面字符串的长度....怎么去掉..不知.....