c++ - 迭代器和重载 << 运算符

Question

我已经截断了这篇文章。为了方便阅读，最初的帖子不见了。相关部分和问题依然存在。

---

更新

我被要求发布的错误是:

[mehoggan@desktop qsort]$ g++ -o qsort -Wall main.cpp
/tmp/ccuAUzlh.o: In function `Sorters::QuickSorter<float>::test_and_sort(float*, int)':
main.cpp:(.text._ZN7Sorters11QuickSorterIfE13test_and_sortEPfi[Sorters::QuickSorter<float>::test_and_sort(float*, int)]+0x61): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& Sorters::operator<< <float>(std::basic_ostream<char, std::char_traits<char> >&, Sorters::Sorter<float>&)'
collect2: ld returned 1 exit status
[mehoggan@desktop qsort]$ 

使用以下代码:

#ifndef SORTERS_H_
#define SORTERS_H_
#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <cmath>
#include <ctime>
#include <assert.h>

using std::vector;
using std::cin;
using std::cout;
using std::endl;
using std::ostream_iterator;
using std::istream_iterator;
using std::next_permutation;
using std::back_inserter;
using std::ostream;

namespace Sorters {
    template<typename T>
    class Sorter {
        public:
            Sorter( ) { };
            virtual ~Sorter( ) { };
            virtual void test_and_sort( T *data, int size )=0;
        protected:
            virtual void sort( typename vector<T>::iterator left, typename vector<T>::iterator right )=0;
            vector<T> m_data;
    };

    template<typename T>
    class QuickSorter : public Sorter<T> {
        public:
            QuickSorter( ) { };
            virtual ~QuickSorter( ) { };
            virtual void test_and_sort( T *data, int size );
        private:
            virtual void sort( typename std::vector<T>::iterator left, typename std::vector<T>::iterator right );
            template<typename S> friend ostream& operator<< ( ostream &stream, Sorter<S> &sorter );
    };
}

template<typename T>
void Sorters::QuickSorter<T>::sort( typename vector<T>::iterator left, typename vector<T>::iterator right ) {

}

template<typename T>
void Sorters::QuickSorter<T>::test_and_sort( T *data, int size ) {
    for( int i=0;i<size;i++ ) {
        vector<T> perm( &data[0], &data[i+1] );
        do {
            cout << (*this) << endl;
            copy( perm.begin( ),perm.end( ),back_inserter( m_data ) );
            this->sort( m_data.begin( ), m_data.end( ) );
        } while( next_permutation( perm.begin( ), perm.end( ) ) );
        m_data.clear( );
    }     
}

template<typename S> ostream& operator<< ( ostream &stream, Sorters::Sorter<S> &sorter ) {
    copy( sorter->m_data.begin( ),sorter->m_data.end( ), ostream_iterator<S>( stream," " ) );
    return stream;
}
#endif

---

更新我写了一个较小的例子，所以我知道我的概念是有效的，当我使用多态性和友元函数时它会变得困惑。

#include <vector>
#include <iostream>
#include <algorithm>
#include <iterator>

using namespace std;

class Sample {
    public:
        Sample( ) { };
        Sample( float *data, int size ) {
            copy(&data[0],&data[size],back_inserter( m_data ) );
        };
        ~Sample( ) { };
    private:
        vector<float> m_data;
        friend ostream& operator<< ( ostream &stream, Sample &s ) {
            copy( s.m_data.begin( ), s.m_data.end( ), ostream_iterator<float>( stream, " " ) );  
            return stream;
        }
};

int main( int argc, char *argv[] ) {
    float data[ ] = {1,2,3,4,5};
    Sample s(data,5);
    cout << s;
}

---

解决方案

Now to write the actual algorithm. I noticed though if I move m_data up to the parrent class I get compiler errors saying that m_data cannot be found. I guess that just means Insertion Sort, Radix Sort, Stooge Sort, ... will all have there own container.

#ifndef SORTERS_H_
#define SORTERS_H_
#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <cmath>
#include <ctime>
#include <assert.h>

using std::vector;
using std::cin;
using std::cout;
using std::endl;
using std::ostream_iterator;
using std::istream_iterator;
using std::next_permutation;
using std::back_inserter;
using std::ostream;

namespace Sorters {
    template<typename T>
    class Sorter {
        public:
            Sorter( ) { };
            virtual ~Sorter( ) { };
            virtual void test_and_sort( T *data, int size )=0;
        protected:
            virtual void sort( typename vector<T>::iterator left, typename vector<T>::iterator right )=0;
    };

    template<typename T>
    class QuickSorter : public Sorter<T> {
        public:
            QuickSorter( ) { };
            virtual ~QuickSorter( ) { };
            virtual void test_and_sort( T *data, int size );
        private:
            vector<T> m_data;
            virtual void sort( typename std::vector<T>::iterator left, typename std::vector<T>::iterator right );
            friend ostream& operator<< ( ostream &stream, const QuickSorter &sorter ) {
                copy( sorter.m_data.begin( ),sorter.m_data.end( ),ostream_iterator<T>( stream," " ) );
                return stream;
            }
    };
}

template<typename T>
void Sorters::QuickSorter<T>::sort( typename vector<T>::iterator left, typename vector<T>::iterator right ) {

}

template<typename T>
void Sorters::QuickSorter<T>::test_and_sort( T *data, int size ) {
    for( int i=0;i<size;i++ ) {
        vector<T> perm( &data[0], &data[i+1] );
        do {
            copy( perm.begin( ),perm.end( ),back_inserter( m_data ) );
            cout << (*this) << endl;
            this->sort( m_data.begin( ), m_data.end( ) );
            m_data.clear( );
        } while( next_permutation( perm.begin( ), perm.end( ) ) );
    }
}
#endif

Answer 1

首先，您要通过打印 this 来打印地址.您需要打印为，

cout << *this << endl;

在您提到的评论中，您遇到了错误。这是因为 operator << () 中的以下行:

vector<S> copy = sorter.m_data;  // <--- where is 'm_data' ??

sorter类型为 class Sorter<S>并且没有 m_data在里面。

要解决此问题，请移动 m_data来自 QuickSorter至 Sorter或重载 operator <<与 QuickSorter<S>& .