findCDs function help

[skiian12]

in the first file how would the findCDs function be written correctly? it's supposed to check what the user typed in with the cds stored. If the user typed in a valid name then it returns something.

#include "CDs.h"
#include <iostream>
#include <string>
#include <cstring>
#include <fstream>

using namespace std;


//
CDs* createCDs(const char* filename,fstream &file)
{
	
	const char* _file;
	int max = 1;
	int min = 0;
	CD** cdPtrArray = new CD*[max];
	CDs* _cds = new CDs;
	
	file.open(filename);
	
	while (!file.eof())
	{
		int year, rating, num_tracks;
		string* title = new string[1];
		string* artist = new string[1];
		string* length = new string[1];
		
		
		file >> artist[0];
		file >> title[0];
		file >> year;
		file >> rating;
		file >> num_tracks;
		if (min == max)
		{
			resize(_cds);
		}
		
		CD* c = createCD(artist, title, year, rating, num_tracks);
		cdPtrArray[min] = c;
		
		for (int i = 0; i < num_tracks; i++)
		{
			file >> length[0];
			file >> title[0];
		}
		min++;
	}	
	
	_cds -> num_cds = min;
	_cds -> max_cds = min;
	_cds -> cd_array = cdPtrArray;
	return _cds;
}

//
void destroyCDs (CDs* cds)
{
	int numCDs = cds -> num_cds;
	CD** _cd = cds -> cd_array;
	
	for ( int i = 0; i < numCDs; i++)
	{
		destroyCD (_cd[i]);
	}
	delete cds;
}

//
void displayCDs (CDs* cds)
{
	int numAlbum = cds -> num_cds;
	
	CD** _cd = cds -> cd_array;
	
	
	for (int i = 0; i < numAlbum; i++)
	{   
        cout << _cd[i] << endl;
	}
	
}

//
void resize (CDs* cds)
{
	int cd_nums = cds -> num_cds;
	int cd_max = cds -> max_cds;
	CD** cd = cds -> cd_array;
	CD** cdPtr = new CD*[cd_max * 2];
	for (int i = 0; i < cd_nums; i++)
	{
		cd[i] = cdPtr[i];
	}
	delete cd;
	
	cd_max * 2;
}

//
CDs* findCDs (CDs* cds, string* artist)
{
	CD* compact = NULL;
	
	int numAlbum = cds -> num_cds;
	CD** _cd = cds -> cd_array;
	
	for (int i = 0; i < numAlbum; i++)
	{
		
		if(artist == compact )
		{
			_cd[i] = compact;
			break;
		}
	}
	return cds;
}

#ifndef CDS_STRUCT
#define CDS_STRUCT

#include "CD.h"

using namespace std;

struct CDs
{
	CD** cd_array;
	int num_cds;
	int max_cds;
};



//
CDs* createCDs(string filename, fstream &file );

//
void destroyCDs(CDs* cds);

//
void displayCDs(CDs* cds);

//
void resize(CDs* cds);

//
CDs* findCDs(CDs* cds, string* artist);


#endif

#include "CD.h"
#include <iostream>

using namespace std;

//
CD* createCD (string* artist, string* title, int year, int rating, int num_tracks)
{
	CD* newCD = new CD;
	newCD -> artist = artist;
	newCD -> title = title;
	newCD -> year = year;
	newCD -> rating = rating;
	newCD -> num_tracks = num_tracks;
	newCD -> track_count = 0;
	newCD -> song_array = new Song*[num_tracks];
	
	return newCD;
}

//
void addSong (CD* cd, string* title, string* length)
{
	Song* song = createSong (title, length);
	
	int songNum = cd->track_count;
	cd -> song_array[songNum] = song;
	cd -> track_count++;
}

//
void destroyCD (CD* cd)
{
	int songNum	= cd->num_tracks;
	Song** cdSongs = cd->song_array;
	
	for ( int i = 0; i < songNum; i++)
	{
		destroySong (cdSongs[i]);
	}
	delete cd;
}

#ifndef CD_STRUCT
#define CD_STRUCT
#include <string>
#include "Song.h"

using namespace std;

struct CD
{
	string* artist;
	string* title;
	int year;
	int rating;
	int num_tracks;
	int track_count;
	Song** song_array;
};

//
CD* createCD(string* artist, string* title, int year, int rating,int num_tracks);

//
void addSong(CD* cd, string* title, string* length);

//
void destroyCD(CD* cd);

#endif

#include "Song.h"
#include <iostream>

using namespace std;

//
Song* createSong (string* title, string* length)
{
	Song* newSong = new Song;
	newSong -> title = title;
	newSong -> length = length;
	return newSong;
}

//
void displaySong (Song* song)
{
	cout << song -> title << "\t" << song -> length << endl;
}

//
void destroySong (Song* song)
{
	delete song;
}


#ifndef SONG_STRUCT
#define SONG_STRUCT

#include <string>

using namespace std;

struct Song
{
	string* title;
	string* length;
};

//
Song* createSong(string* title, string* length);

//
void displaySong(Song* song);

//
void destroySong(Song* song);

#endif 

[MikeyBoy]

Firstly, please stop spamming the forum with multiple threads for the same thing. It's annoying, and it wastes peoples' time, because they answer on one thread, without realising someone else may have answered on another.

Your findCDs function is a bit of a mess. You never set the value of compact to be anything, so it's always NULL, but you try and use it to compare with artist. Also, compact is a pointer to a CD, while artist is a pointer to a string, so even if CD was pointing to something valid, it couldn't possibly be a sensible comparison.

You seem to be confused as to what cds represents. At lines 106 and 109, you use it as if it's the existing database of CD's, in which you're trying to find an artist. But at lines 107 and 114, you're using it as if it was an object for storing the results of the search. Which is it?

To find a list of CD's of a given artist, here's how I would do it:

1) Your function needs to take as read-only (i.e. const) arguments, a pointer to the database of CDs, and the name of the artist.

2) Your function needs to iterate over all the CD's in the database, comparing the artist of each CD to the artist passed in as an argument.

3) If the artist of any CD matches the argument, store a pointer to the CD in a separate object containing the results. A vector of pointers to CD would be a good choice here,

4) Pass that object containing the results back to the calling code - either by returning it, or using a third argument that's passed by reference.

EDIT: dlhayden's comments on one of your duplicate threads are also relevant here.