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Reading a Matrix txt file and storing as an array

Answer 1

+1 A:

Does it even compile? I get ~7 errors. A sample:

strtok(cities, "\n");

strtok()'s first argument is a char * and not a std::string.

Does this help?

void LoadCities()
{
  std::vector<double> f((std::istream_iterator<double>
       (std::ifstream("city.txt"))), /* replace filename with your own */
    (std::istream_iterator<double>()));
  if (!f.empty()) {
    std::cout << f.size() << "\n";
    /* print an arbitrary data point with 2 places of decimal */
    std::cout << std::setprecision(2) << f[ 0 ] << std::endl; 

  }
}

Working with matrices doesn't mean you need to have a multidimensional array. Especially, with 2D arrays. Of course it's easier to read and write ;)

dirkgently 2009-02-21 13:30:58

as it is it doesn't compile. Only way to compile it is to delete everything from 'cities = ..." to the end and simply have: CityFile.read(buffer,length);, cout.write(buffer,length); CityFile.close(); - which doesn't help me much

Temperedsoul 2009-02-21 16:22:54

@Temperedsoul: So, now do you have it fixed? If you do, why don't you mark schnaader's solution as accepted?

dirkgently 2009-02-21 16:39:34

Answer 2

+4 A:

How about this? (KISS solution)

void LoadCities() {
  int x, y;
  ifstream in("Cities.txt");

  if (!in) {
    cout << "Cannot open file.\n";
    return;
  }

  for (y = 0; y < 15; y++) {
    for (x = 0; x < 15; x++) {
      in >> distances[x][y];
    }
  }

  in.close();
}

Works for me. Might not be that complex and perhaps isn't very performant, but as long as you aren't reading a 1000x1000 array, you won't see any difference.

schnaader 2009-02-21 13:51:48

Nice and simplistic, however for some reason its outputting 0 or every value when I test it. E.g adding the following right after the << operation: "cout << x << "\t" << y << '\t' << distances[x][y] << endl;"

Temperedsoul 2009-02-21 16:17:14

Hm.. works here (using G++).

schnaader 2009-02-21 16:39:13

@Temperedsoul: Look at your data. It's double, but has no significant part after the decimal. If you want a 5.0 you'd need to do tell cout so. I'll update my example.

dirkgently 2009-02-21 16:40:41

Answer 3

A:

You probably want something simpler, like this:

std::vector<std::vector<std::string> > LoadCities(const std::string &filename)
{
    using namespace std;

    ifstream file;
    file.open(filename, ios::in | ios::out);

    if(!file.is_open()) {
        // error
        return vector<vector<double> >();
    }

    vector<vector<double> > data;
    string line;

    while(!std::getline(file, line, '\n').eof()) {
        istringstream reader(line);

        vector<double> lineData;

        string::const_iterator i = line.begin();

        while(!reader.eof()) {
            double val;
            reader << val;

            if(reader.fail())
                break;

            lineData.push_back(val);
        }

        data.push_back(lineData);
    }

    return data;
}

Basically you use streams to input the data. I'm probably doing something wrong (I have never dealt with iostreams ;P) but this should give you the general idea of how to structure a matrix reader.

strager 2009-02-21 13:51:50

Results in 4 errors, three of them C2664 - 'function' : cannot convert parameter number from 'type1' to 'type2' - I will see if I can clear them up.

Temperedsoul 2009-02-21 16:25:26

Answer 4

A:

Here is how I would load/save it:

#include <iostream>
#include <fstream>
#include <string>

int width = 0;
int height = 0;
double **distances;

void WriteDouble( std::ofstream &stream, double toWrite )
{
    char buffer[8];
    memcpy( buffer, &toWrite, 8 );
    stream.write( buffer, 8 );
}

void WriteInt( std::ofstream &stream, int toWrite )
{
    char buffer[4];
    memcpy( buffer, &toWrite, 4 );
    stream.write( buffer, 4 );
}

double ReadDouble( std::ifstream &stream )
{
    double d = 0;
    stream.read( (char *)&d, 8 );
    return d;
}

int ReadInt( std::ifstream &stream )
{
    int i = 0;
    stream.read( (char *)&i, 4 );
    return i;
}

void Save()
{
    std::ofstream stream( "cities", std::ios::out | std::ios::binary );

    if( !stream.good() ) {
     throw std::exception( "Error opening stream" );
    }

    WriteInt( stream, width );
    WriteInt( stream, height );

    for( int x = 0; x < width; x++ ) {
     for( int y = 0; y < height; y++ ) {
      WriteDouble( stream, distances[x][y] );
     }
    }

    stream.close();
}

void Load()
{
    std::ifstream stream( "cities", std::ios::in | std::ios::binary );

    if( !stream.good() ) {
     throw std::exception( "Error opening stream" );
    }

    width = ReadInt( stream );
    height = ReadInt( stream );

    distances = new double *[width];

    for( int i = 0; i < width; i++ ) {
     distances[i] = new double[height];
    }

    for( int x = 0; x < width; x++ ) {
     for( int y = 0; y < height; y++ ) {
      distances[x][y] = ReadDouble( stream );
     }
    }

    stream.close();
}

void RunSaveTest()
{
    width = 15;
    height = 15;

    distances = new double *[width];

    for( int i = 0; i < width; i++ ) {
     distances[i] = new double[height];
    }

    for( int x = 0; x < width; x++ ) {
     for( int y = 0; y < height; y++ ) {
      distances[x][y] = (double)x / (double)( y + 1 );
      std::cout << distances[x][y] << std::endl;
     }
    }

    Save();
}

void RunLoadTest()
{
    Load();

    for( int x = 0; x < width; x++ ) {
     for( int y = 0; y < height; y++ ) {
      std::cout << distances[x][y] << std::endl;
     }
    }
}

int main()
{
    RunSaveTest();
    // RunLoadTest();

    return 0;
}

kitchen 2009-02-21 20:53:51

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Reading a Matrix txt file and storing as an array

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