Accelerated C++ Exercises Ch14

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本文详细介绍了C++中模板和智能指针的使用方法，通过实例展示了如何在实际项目中提高代码的灵活性和安全性。重点讨论了如何利用智能指针实现资源管理，避免内存泄漏，并通过模板技术实现通用代码。

14-1
Implement the comparison operation that operates on Ptr.

bool compare_Core_handles(const Handle<Core>& lhs,const Handle<Core>& rhs)  
{  
    return compare(*lhs,*rhs);  
}

14-4
Reimplement the Str class to use the final version of Ptr.

//"Ptr.h"

#ifndef Ptr_H
#define Ptr_H

template <class T> class Ptr {
public:
    Ptr() : refptr(new size_t(1)), p(0) { }
    Ptr(T* t) : refptr(new size_t(1)), p(t) { }
    Ptr(const Ptr& h) : refptr(h.refptr), p(h.p)
    {
        ++*refptr;
    }

    void make_unique();
    Ptr& operator=(const Ptr&);
    ~Ptr();

    operator bool() const
    {
        return p;
    }
    T& operator*() const
    {
        if (p)
            return *p;
        throw std::runtime_error("unbound Ptr");
    }
    T* operator->() const {
        if (p)
            return p;
        throw std::runtime_error("unbound Ptr");
    }

private:
    T* p;
    size_t* refptr;
};

template<class T> void Ptr<T>::make_unique()
{
    if (*refptr != 1)
    {
        --*refptr;
        refptr = new size_t(1);
        p = p ? clone(p) : 0;
    }
}

template<class T> T* clone(const T* vp)
{
    return new T(*vp);
}

template<class T> Ptr<T>& Ptr<T>::operator=(const Ptr& rhs)
{
    ++*rhs.refptr;
    // free the left-hand side, destroying pointers if appropriate 
    if (--*refptr == 0) {
        delete refptr;
        delete p;
    }

    // copy in values from the right-hand side 
    refptr = rhs.refptr;
    p = rhs.p;
    return *this;
}

template<class T> Ptr<T>::~Ptr()
{
    if (--*refptr == 0) {
        delete refptr;
        delete p;
    }
}

#endif// Ptr_H

//"Str.h"

#ifndef Str_H
#define Str_H
#include <iostream>
#include <iterator>
#include "Vec.h"
#include "Ptr.h"
#include <string.h>
#include <iterator>

class Str
{
    friend std::istream& operator>> (std::istream&, Str&);
    friend Str operator+ (const Str&, const char*);
    friend Str operator+ (const char*, const Str&);

public:
    typedef Vec<char>::size_type size_type;
    typedef char* iterator;
    typedef const char* const_iterator;

    Str() : data(new Vec<char>) { }
    Str(size_type n, char c) : data(new Vec<char>(n, c)) { }
    Str(const char* cp) : data(new Vec<char>)
    {
        std::copy(cp, cp + std::strlen(cp), std::back_inserter(*data));
    }
    template <class In> Str(In b, In e) : data(new Vec<char>)
    {
        std::copy(b, e, std::back_inserter(*data));
    }

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

    iterator begin()
    {
        data.make_unique();
        return data->begin();
    }
    const_iterator begin() const
    {
        return data->begin();
    }
    iterator end()
    {
        data.make_unique();
        return data->end();
    }
    const_iterator end() const
    {
        return (*data).end();
    }

    Str& operator+= (const Str& s);
    char& operator[](size_type i)
    {
        data.make_unique();
        return (*data)[i];
    }
    const char& operator[](size_type i) const
    {
        return (*data)[i];
    }
    operator void*() const
    {
        return data->empty() ? 0 : (void*)1;
    }

    std::istream& getline(std::istream& is)
    {
        data.make_unique();

        data->clear();
        char c;

        while (is.get(c) && isspace(c));

        if (is)
        {
            do
            {
                (*data).push_back(c);
            } while (is.get(c) && c != '\n');

            if (is)
                is.unget();
        }

        return is;
    }
    template <class In> void insert(iterator iter, In b, In e)
    {
        data.make_unique();
        data->insert(iter, b, e);
    }

private:
    Ptr< Vec<char> > data;
};

std::istream& operator>> (std::istream& is, Str& s)
{
    s.data.make_unique();

    s.data->clear();
    char c;

    while (is.get(c) && isspace(c));

    if (is)
    {
        do
        {
            s.data->push_back(c);
        } while (is.get(c) && !isspace(c));

        if (is)
            is.unget();
    }

    return is;
}

std::ostream& operator<< (std::ostream& os, const Str& s)
{
    //for (Str::size_type i = 0; i != s.size(); ++i)
    //{
    //  os << s[i];
    //}
    std::ostream_iterator<char> iter(os);
    for (Str::size_type i = 0; i != s.size(); i++)
    {
        *iter++ = s[i];
    }

    return os;
}

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

Str operator+ (const Str& x, const Str& y)
{
    Str temp;
    temp = x;
    temp += y;

    return temp;
}
Str operator+ (const Str& x, const char* y)
{
    Str temp;
    temp = x;
    std::copy(y, y + std::strlen(y), std::back_inserter(*temp.data));

    return temp;
}
Str operator+ (const char* x, const Str& y)
{
    Str temp;
    std::copy(x, x + std::strlen(x), std::back_inserter(*temp.data));
    temp += y;

    return temp;
}

bool operator< (const Str& x, const Str& y)
{
    Str::size_type i = 0;
    while (i != x.size() && i != y.size())
    {
        if (x[i] == y[i])   ++i;
        else return x[i] < y[i] ? true : false;
    }
    if (!x[i]) return true;
    else return false;
}
bool operator> (const Str& x, const Str& y)
{
    Str::size_type i = 0;
    while (i != x.size() && i != y.size())
    {
        if (x[i] == y[i])   ++i;
        else return x[i] > y[i] ? true : false;
    }
    if (!y[i]) return true;
    else return false;
}
bool operator== (const Str& x, const Str& y)
{
    Str::size_type i = 0;
    while (i != x.size() && i != y.size())
    {
        if (x[i] == y[i])   ++i;
        else return false;
    }
    if (!x[i] && !y[i]) return true;
    else return false;
}
bool operator!= (const Str& x, const Str& y)
{
    return !(x == y);
}


#endif // Str_H

//"Vec.h"

#ifndef Vec_H
#define Vec_H
#include <memory>
#include <cstddef>
#include <algorithm>

template <class T>
class Vec
{
public:
    typedef T* iterator;
    typedef const T* const_iterator;
    typedef T& reference;
    typedef const T& const_reference;
    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());
    }
    template <class In> Vec(In b, In e)
    {
        create();
        std::copy(b, e, std::back_inserter(*this));
    }
    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);
    }
    template <class In> void insert(iterator iter, In b, In e)
    {
        size_type new_size = (limit - data) + (e - b);
        iterator new_data = alloc.allocate(new_size);
        iterator temp1 = std::uninitialized_copy(data, iter, new_data);
        iterator temp2 = std::uninitialized_copy(b, e, temp1);
        iterator new_avail = std::uninitialized_copy(iter, avail, temp2);
        uncreate();
        data = new_data;
        avail = new_avail;
        limit = data + new_size;
    }
    template <class In> void assign(In array[])
    {
        In *array_end = array;
        while (*array_end) array_end++;
        size_type new_size = array_end - array;
        iterator new_data = alloc.allocate(new_size);
        iterator new_avail = std::uninitialized_copy(array, array_end, new_data);
        uncreate();
        data = new_data;
        avail = new_avail;
        limit = data + new_size;
    }

    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;
    }

    void clear()
    {
        uncreate();
    }
    iterator erase(iterator it)
    {
        for (iterator i = it; i != avail; ++i)
        {
            alloc.destroy(i);
            if ((i + 1) != avail) alloc.construct(i, *(i + 1));
        }
        --avail;
        return it;
    }

    bool empty() const
    {
        return data == avail;
    }

private:
    iterator data;
    iterator avail;
    iterator limit;

    std::allocator<T> alloc;
    void create();
    void create(size_type, const T&);
    void create(const_iterator, const_iterator);
    void uncreate();
    void grow();
    void unchecked_append(const T&);
};
template <class T>
Vec<T>& Vec<T>::operator=(const Vec& rhs)
{
    if (&rhs != this)
    {
        uncreate();
        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);
    limit = avail = data + n;
    std::uninitialized_fill(data, limit, val);
}

template <class T>
void Vec<T>::create(const_iterator i, const_iterator j)
{
    data = alloc.allocate(j - i);
    limit = avail = std::uninitialized_copy(i, j, data);
}

template <class T>
void Vec<T>::uncreate()
{
    if (data)
    {
        iterator it = avail;
        while (it != data)
            alloc.destroy(--it);
        alloc.deallocate(data, limit - data);
    }
    data = limit = avail = 0;
}

template <class T>
void Vec<T>::grow()
{
    size_type new_size = std::max(2 * (limit - data), ptrdiff_t(1));
    iterator new_data = alloc.allocate(new_size);
    iterator new_avail = std::uninitialized_copy(data, avail, new_data);
    uncreate();
    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);
}
#endif // Vec_H

//"main.h"

#define  _SCL_SECURE_NO_WARNINGS
#include "Str.h"
#include <string>

using namespace std;

int main()
{
    Str s1("abc"), s2;
    string str = "hello~";
    Vec<char> v1(str.begin(), str.end());

    for (Vec<char>::size_type i = 0; i != v1.size(); i++)
    {
        cout << v1[i];
    }
    cout << endl;

    cout << s1.size() << endl << s2.size() << endl;

    if (s1){ cout << "s1 exist" << endl; }
    else { cout << "s1 null" << endl; }
    if (s2){ cout << "s2 exist" << endl; }
    else { cout << "s2 null" << endl; }

    s2.getline(cin);

    if (s1 < s2)
    {
        cout << "<" << endl;
    }
    else if (s1 == s2)
    {
        cout << "==" << endl;
    }
    else
    {
        cout << ">" << endl;
    }

    cout << s1 << endl << s2 << endl;
    cout << s1.size() << endl << s2.size() << endl;

    cout << "test insert:" << endl;
    s2.insert(s2.begin() + 1, s1.begin(), s1.end());
    cout << s2 << endl;
    cout << "test assign:" << endl;
    v1.assign("v1 is assigned");
    for (Vec<char>::size_type i = 0; i != v1.size(); i++)
    {
        cout << v1[i];
    }
    cout << endl;

    system("pause");
}