Re: Read 2d Array from Text File-

"RyanS09" <RyanS09@gmail.com> wrote in message
news:1180472403.866354.54880@p77g2000hsh.googlegroups.com...


This is somewhat trivial and may be homework. There are a few ways to do
it, I decided to go ahead and code it up the way I would do it. Others may
use different methods ( InputFile >> SomeFloat instead of a string, for
example).

Code was tested and ran with a simple data file of 10 floating point values
per line. It displayed the appropriate error message if a line had too many
or too less values. A possible optimization (which I would probably do if
this was in production) would be to push an empty vector<float> to data,
grab an iterator to it and push the data into that, rather than pushing the
full vector which requires a copy of the values. Pre-sizing the vector may
help, but I think that 10 floats is less than the default allotment anyway
(didn't bother to test since I'm not going to be using this code).

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

static const int LineLength = 10;

void Pause()
{
    std::string Wait;
    std::getline( std::cin, Wait );
}

int main()
{
    std::ifstream InputFile( "testinput.txt" );
    if ( ! InputFile.is_open() )
    {
        std::cout << "Error opening testinput.txt!" << std::endl;
        Pause();
        return 1;
    }

    std::vector< std::vector< float > > Data;

    std::string Input;
    while ( std::getline( InputFile, Input ) )
    {
        // Input contains entire line
        std::stringstream Parse;
        Parse << Input;
        float Value;
        std::vector<float> Line;
        while ( Parse >> Value )
            Line.push_back( Value );
        if ( Line.size() != LineLength )
        {
            std::cout << "Line " << Data.size() + 1 << " expected " <<
LineLength << " values, received " << Line.size() << " values, aborting." <<
std::endl;
            Pause();
            return 1;
        }
        Data.push_back( Line );
    }

    // close not specifically needed, will be called by destructor when
    // ifstream goes out of scope, but I always call it anyway.
    InputFile.close();

    // At this point, all read values are in our vector of vector of floats
named Data.
    std::cout << "Data:\n";
    for ( size_t i = 0; i < Data.size(); ++i )
    {
        for ( size_t j = 0; j < Data[i].size(); ++j )
            std::cout << Data[i][j] << " ";
        std::cout << "\n";
    }

    Pause();

    return 0;
}