Read data from a file individually and multiply the two columns in C++

Question

I have a data file \"1.dat\" which has 4 columns and 250 rows.

I need to read each row and process it such as to multiply two columns [col1 and col2].

Can yo

Answer 1

http://www.cplusplus.com/doc/tutorial/files/ Here's a few tips on how to read a file using C++, after that you're going to need to cast a string into an integer or float depending.

Answer 2

Assuming the file has delimited data, you will probably:

• use ifstream to open the file
• use std::getline( ifstream, line ) to read a line. You can do this in a loop. line should be of type std::string
• process each line using istringstream( line ) then reading these into your element.

To store the read data you could use vector< vector< double > > or some kind of matrix class.

with vector<vector<double> >

ifstream ifs( filename );
std::vector< std::vector< double > > mat;
if( ifs.is_open() )
{
   std::string line;
   while( std::getline( ifs, line ) )
   {
       std::vector<double> values;
       std::istringstream iss( line );
       double val;
       while( iss >> val )
       {
          values.push_back( val );
       }
       mat.push_back( values );
   }
}