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#1
May 1st, 2008, 01:24 PM
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File IO - Replacing strings in vectors
i'm working on the "removesong" function. i need to check the vectors that already have the data separated and stored in them, and i need to see if the entered song title and artist name exist. if they do, i need to replace that same vector location with an empty string. i can't seem to get this to work, i need to also right the new vectors back into the file. it isn't supposed to completely overwrite the file, just remove the specified data.
file: Code:
Here it Goes Again OK Go Rock Fade to Black Metallica Metal Enter Sandman Metallica Metal Walk Pantera Metal Learn to Fly Foo Fighters Rock I Wanna Be Sedated The Ramones Punk Stairway to Heaven Led Zeppelin Rock Words Paul Van Dyk Electronic Punk Ferry Corsten Electronic Let Go Paul Van Dyk Electronic program: Code:
#include <iostream> // For input and output to the monitor
#include <fstream> // For file input and output (given)
#include <string> // For text data
#include <vector> // library for using vectors
using namespace std; // To make is easier put this in global namespace
void addsong(vector<string>&, vector<string>&, vector<string>&);
// function: this adds songs to the library
// parameters: string title, string artist, string genre
// functionality: prompts the user for the parameters and checks to make sure
// the song isn't already in the library
void removesong(vector<string>& titles, vector<string>& artists, vector<string>& genres);
// function: this removes songs from the library and replaces them with whitespace
// parameters: title, artist, genre
// funtionality: prompts user for song and artist of song wishing to remove
void searchsong(vector<string>& titles, vector<string>& artists, vector<string>& genres);
int main()
{
vector<string> titles;
vector<string> artists;
vector<string> genres;
ifstream in_stream;
in_stream.open("music_library.txt");
int i=1;
if (in_stream.fail( ))
{
cout << "Unable to open file.\n";
}
else
{
string title, artist, genre;
while(!in_stream.eof())
{
if((i%3==1)||i==1)
{
getline(in_stream, title);
titles.push_back(title);
i++;
}
if((i%3==2)||i==2)
{
getline(in_stream, artist);
artists.push_back(artist);
i++;
}
if((i%3==0)||i==3)
{
getline(in_stream, genre);
genres.push_back(genre);
i++;
}
}
}
cout << "Titles size: " << titles.size() << endl;
cout << "Artist size: " << artists.size() << endl;
cout << "Genre size: " << genres.size() << endl;
int choice;
do
{
cout << "\n\n1. Add a new song\n";
cout << "2. Remove an existing song\n";
cout << "3. Search for a song\n";
cout << "4. Quit program\n";
cin >> choice;
switch(choice)
{
case 1: //user wants to add a song
addsong(titles, artists, genres);
break;
case 2: //user wants to remove an existing song
removesong(titles, artists, genres);
break;
case 3: //user wants to search for a song
searchsong(titles, artists, genres);
break;
case 4: //user wants to quit program
cout << "GOODBYE!\n";
break;
}
}while(choice !=4);
cin.get();
in_stream.close( );
return 0;
}
void addsong(vector<string>& titles, vector<string>& artists, vector<string>& genres)
{
ofstream in_stream;
in_stream.open("music_library.txt", ios::app);
string t_title, a_artist, g_genre;
if(in_stream.fail( ))
{
cout << "File failed to open." << endl;
}
cout << "Enter the title name: " << endl;
cin.ignore(100, '\n');
getline(cin, t_title);
titles.push_back(t_title);
cout << "Enter the artist name: " << endl;
getline(cin, a_artist);
artists.push_back(a_artist);
cout << "Enter the genre: " << endl;
getline(cin, g_genre);
genres.push_back(g_genre);
for(unsigned int i = 0; i < titles.size(); ++i)
{
if(t_title.compare(titles[i]) !=0&&(a_artist.compare(artists[i])!=0))
//compare is a function that i found on http://www.cplusplus.com/
{
cout << "Items have been added to library" << endl;
titles.push_back(t_title);
artists.push_back(a_artist);
genres.push_back(g_genre);
int length_t = t_title.length( );
int length_a = a_artist.length( );
int length_g = g_genre.length( );
if(length_t==0||length_a==0||length_g==0)
{
if(length_t==0&&length_a > 0&&length_g > 0)
{
in_stream << endl << a_artist << endl << g_genre;
}
if(length_a==0&&length_t > 0&&length_g >0)
{
in_stream << endl << t_title << endl << g_genre;
}
if(length_g==0&&length_t > 0&&length_a >0)
{
in_stream << endl << t_title << endl << a_artist;
}
}
if(length_g==0&&length_a==0)
{
cout << "No genre type or artist name added to library." << endl;
in_stream << endl << t_title;
}
if(length_g==0&&length_t==0)
{
cout << "No genre type or song title were added to the library." << endl;
in_stream << endl << a_artist;
}
if(length_a==0&&length_t==0)
{
cout << "No artist name or song title were added to the library." << endl;
in_stream << endl << g_genre;
}
if(length_g > 0 && length_t > 0 && length_a > 0)
{
in_stream << endl << t_title << endl << a_artist << endl << g_genre;
}
return;
}
else
cout << "Item exist!" << endl;
return;
}
in_stream.close( );
}
void removesong(vector<string>& titles, vector<string>& artists, vector<string>& genres)
{
ofstream in_stream;
in_stream.open("music_library.txt");
string t_title, a_artist, g_genre;
cout << "Please enter the song title which you wish to remove: " << endl;
cin.ignore(100, '\n');
getline(cin, t_title);
titles.push_back(t_title);
cout << "Please enter the corresponding artist name: " << endl;
getline(cin, a_artist);
artists.push_back(a_artist);
for(unsigned int i = 0; i < titles.size(); ++i)
{
if(t_title.compare(titles[i]) !=0&&(a_artist.compare(artists[i])!=0))
{
cout << "Data not found in library!" << endl;
while(int j=0 < titles.size())
{
in_stream << titles[j] << artists[j] << genres[j];
j++;
return;
}
}
else
titles[i] = ' ';
artists[i] = ' ';
genres[i] = ' ';
titles.push_back(t_title);
artists.push_back(a_artist);
genres.push_back(g_genre);
in_stream << titles[i] << artists[i] << genres[i];
cout << "Song data has been removed." << endl;
return;
}
in_stream.close();
}
void searchsong(vector<string>& titles, vector<string>& artists, vector<string>& genres)
{
ifstream in_stream;
ofstream library;
in_stream.open("music_library.txt");
library.open("library.txt");
int choice;
string t_title, a_artist, g_genre;
do
{
cout << "1. Search by song title." << endl;
cout << "2. Search by artist." << endl;
cout << "3. Search by genre." << endl;
cin >> choice;
switch(choice)
{
case 1:
cout << "Enter song title: " << endl;
cin.ignore(100, '\n');
getline(cin, t_title);
for(unsigned int i = 0; i < titles.size(); i++)
{
if(t_title.compare(titles[i])==0)
{
cout << titles[i] << endl << artists[i] << endl << genres[i] << endl << endl;
}
}
break;
case 2:
cout << "Enter artist: " << endl;
cin.ignore(100, '\n');
getline(cin, a_artist);
for(unsigned int i = 0; i < artists.size(); i++)
{
if(a_artist.compare(artists[i])==0)
{
cout << titles[i] << endl << artists[i] << endl << genres[i] << endl << endl;
}
}
break;
case 3:
cout << "Enter genre: " << endl;
cin.ignore(100, '\n');
getline(cin, g_genre);
for(unsigned int i = 0; i < genres.size(); i++)
{
if(g_genre.compare(genres[i])==0)
{
cout << titles[i] << endl << artists[i] << endl << genres[i] << endl << endl;
}
}
break;
}
}while(!in_stream.eof());
in_stream.close();
library.close();
}
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#2
May 6th, 2008, 08:25 AM
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To actually remove an element from a vector, try
erase(vectorname[5]); This will then move all the subsequent elements back one step, as if it didn't exist. This is probably better than setting the strings to empty ones. Then, save the vector back to the file, overwriting it. "Simply" modifying the file will be far more difficult. ----- I would like to introduce you to the concept of structures and classes. Given Code:
struct Track {
string artist;
string title;
string genre;
};
you would need only a single vector<Track> tracks which would be easier to pass around to functions, and the delete function would need only one call to erase. (Even if you added more fields, like length, rating, etc.) It's even possible to make it such that you can just use infile >> mytrack; instead of that long if-else chain. The 'detail code' still has to be written somewhere, but it's out of the way, making it quite clear to a human reader what the function is doing with less analyzing. Also, consider the changes your program would have to go through to add e.g. a "length" field, with your old version vs this. If you don't see it as much of a bother, try considering how it would be if you continued working on this as a "real" application, the kind that grows to 100s or 1000s of functions, and then wanted to add a "rating" field. Though you'll probably learn about this sooner or later anyway, I thought I'd show you a convenient tool for the job you are doing right now.
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