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2009年12月21日

條款2：盡量以CONST，ENUM，INLINE替換#DEFINE

類中定義常量：static const int numturns = 5;

這是聲明式而非定義式。若不需取它們的地址，無須提供定義式。定義式如下：

const int GamePlayer::NumTurns;

一個class需要常量值，定義如下：

enum{NumTurns = 5};

int scores[NumTurns];

關于“形似函數的宏，最好改用inline函數替換#defines”

但，經驗證明。宏的速度要比用inline的方法快。

在一些對速度要求非常嚴格的項目中，這個方面還是要有所取舍的。

posted @ 2009-12-21 00:18 蜜蜂閱讀(238) | 評論 (1) | 編輯收藏

vector

#include <vector>
#include <string>
#include <algorithm>
#include <iterator>
#include <iostream.h>
// #include <iostream>

class GreaterThan {
public:
    GreaterThan( int size = 6 ) : _size( size ){}
    int size() { return _size; }

    bool operator()(const string & s1) {
        return s1.size() > 6;
        }

private:
    int _size;
};

template <class Type>
class PrintElem {
public:
    void operator()( const Type &elem )
    {
        ++_cnt;
        if ( _cnt % 8 == 0 ) { cout << endl; }
        cout << elem << " ";
    }

private:
    static int _cnt;
};

template < class Type >
       int PrintElem<Type>::_cnt = 0;

class LessThan {
public:
    bool operator()(const string & s1, const string & s2 ) {
         return s1.size() < s2.size();
        }
};

typedef vector<string, allocator> textwords;

void process_vocab( vector<textwords, allocator> *pvec )
{
    if ( ! pvec )
         // issue warning message
         return;

    vector< string, allocator > texts;

    vector<textwords, allocator>::iterator iter = pvec->begin();
    for ( ; iter != pvec->end(); ++iter )
              copy( (*iter).begin(), (*iter).end(), back_inserter( texts ));

    // sort the elements of texts
    sort( texts.begin(), texts.end() );
    for_each( texts.begin(), texts.end(), PrintElem<string>() );

    cout << endl << endl;

    // delete all duplicate elements
    vector<string, allocator>::iterator it;
    it = unique( texts.begin(), texts.end() );
    texts.erase( it, texts.end() );
    for_each( texts.begin(), texts.end(), PrintElem<string>() );

    cout << endl << endl;

    stable_sort( texts.begin(), texts.end(), LessThan() );
    for_each( texts.begin(), texts.end(), PrintElem<string>() );

    cout << endl << endl;

    // count number of strings greater than length 6
    int cnt = 0;

    // obsolete form of count -- standard changes this
    count_if( texts.begin(), texts.end(), GreaterThan(), cnt );

    cout << "Number of words greater than length six are "
             << cnt << endl;

    //

    static string rw[] = { "and", "if", "or", "but", "the" };
    vector<string,allocator> remove_words( rw, rw+5 );

    vector<string, allocator>::iterator it2 = remove_words.begin();
    for ( ; it2 != remove_words.end(); ++it2 ) {
        int cnt = 0;
        // obsolete form of count -- standard changes this
            count( texts.begin(), texts.end(), *it2, cnt );

        cout << cnt << " instances removed:  "
                 << (*it2) << endl;

            texts.erase(
                remove(texts.begin(),texts.end(),*it2),
                texts.end()
           );
       }

    cout << endl << endl;
    for_each( texts.begin(), texts.end(), PrintElem<string>() );
}

typedef vector<string,allocator>::difference_type diff_type;
#include <fstream.h>

main()
{
     vector<textwords, allocator> sample;
     vector<string,allocator>       t1, t2;
     string               t1fn, t2fn;

     cout << "text file #1: "; cin >> t1fn;
     cout << "text file #2: "; cin >> t2fn;

     ifstream infile1( t1fn.c_str());
     ifstream infile2( t2fn.c_str());

     istream_iterator< string, diff_type > input_set1( infile1 ), eos;
     istream_iterator< string, diff_type > input_set2( infile2 );

     copy( input_set1, eos, back_inserter( t1 ));
     copy( input_set2, eos, back_inserter( t2 ));

     sample.push_back( t1 ); sample.push_back( t2 );
     process_vocab( &sample );
}

posted @ 2009-12-21 00:14 蜜蜂閱讀(212) | 評論 (0) | 編輯收藏

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條款2：盡量以CONST，ENUM，INLINE替換#DEFINE

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