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.....