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#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <sstream>

#include "FilmScore.h"
#include "HashedDictionary.h"

using namespace std;

string getFileName();
bool createRecord( const FilmScore & newRecord, const string & inputLine );
void eraseTrailingSpaces( string & input );
void extractData( string & composer, string & filmTitle, string & label, string & catalogNum, string & recordingYear, string & releaseYear, const string & inputLine );
void pause();

template <typename T>
void readFile( vector<T> & p_records );

template <typename T>
bool isDuplicate( const vector<T> & records, const T & newRecord );

template <typename T>
void displayVector( const vector<T> & vec );

const unsigned COMPOSER_FIELD_LENGTH = 24,
               FILM_TITLE_FIELD_LENGTH = 40,
               LABEL_FIELD_LENGTH = 16,
               CATALOG_NUM_FIELD_LENGTH = 24,
               RECORDING_YEAR_FIELD_LENGTH = 8,
               CD_RELEASE_YEAR_FIELD_LENGTH = 4;

const unsigned COMPOSER_BEGIN = 0,
               FILM_TITLE_BEGIN = COMPOSER_FIELD_LENGTH,
               LABEL_BEGIN = FILM_TITLE_BEGIN + FILM_TITLE_FIELD_LENGTH,
               CATALOG_NUM_BEGIN = LABEL_BEGIN + LABEL_FIELD_LENGTH,
               RECORDING_YEAR_BEGIN = CATALOG_NUM_BEGIN + CATALOG_NUM_FIELD_LENGTH,
               CD_RELEASE_YEAR_BEGIN = RECORDING_YEAR_BEGIN + RECORDING_YEAR_FIELD_LENGTH;

const string DEFAULT_FILE_NAME = "Soundtrack.txt";

template <class ItemType>
ostream& operator<<( ostream & out, const HashedDictionary<ItemType> & table )
{
    for ( unsigned i = 0; i < table.hashTableSize; i++ )
        if ( table.hashTable[i] != NULL )
            table.displayChain( out, table.hashTable[i] );

    return out;
}

int main()
{
    vector<FilmScore> records;

    readFile( records );

    pause();

    HashedDictionary<FilmScore> hashTable( records.size() * 3 );

    // load the films into the hash table:

    for ( size_t i = 0; i < records.size(); i++ )
        hashTable.add( records[i] );

    try
    {
        cout << "Get item with key \"FSMBox 03 Disc 8\":\n";
        cout << hashTable.getItem( static_cast<string>( "FSMBox 03 Disc 8" ) ); 
    }
    catch ( PrecondViolatedExcep e )
    {
        cout << e.what();
    }

    cout << endl << endl;

    try
    {
        cout << "Get item with key \"FSMBox 07 Disc 8\":\n";
        cout << hashTable.getItem( static_cast<string>( "FSMBox 07 Disc 8" ) );
    }
    catch ( PrecondViolatedExcep e )
    {
        cout << e.what();
    }

    cout << endl << endl;

    pause();

    cout << "Listing all items in the has table: (There are " << hashTable.getItemCount() << " items in the table)\n\n";

    cout << hashTable;

    return 0;
}

错误：

error LNK2019: unresolved external symbol "class std::basic_ostream<char,struct std::char_traits<char> > & __cdecl operator<<(class std::basic_ostream<char,struct std::char_traits<char> > &,class HashedDictionary<class FilmScore> const &)" (??6@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@AAV01@ABV?$HashedDictionary@VFilmScore@@@@@Z) referenced in function __catch$_main$0
1>C:\Users\user\Desktop\CS M20A\Topic E2 Project\Debug\Topic E2 Project.exe : fatal error LNK1120: 1 unresolved externals

我查看了其他遇到此错误的人的问题，似乎它与没有定义的函数有关，但在这种情况下 operator<< 定义在 main() 的正上方。我不知道问题可能是什么。

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