Reading a file with data

Question

Hi,

I am new to c++ programming. I am trying to read data in a file whose contents are as follows:

AS G02  2009 01 30 00 00  0.000000  2    1.593749310156e-04  4.717165038980e-11
AS G03  2009 01 30 00 00  0.000000  2    3.458468649886e-04  4.542246790350e-11
AS G04  2009 01 30 00 00  0.000000  2   -3.176765824224e-04  2.733827659950e-11
AS G05  2009 01 30 00 00  0.000000  2   -6.126657874204e-04  3.269050090460e-11

I would then write this data to an output file for processing later. The output should like this:

02  2009 01 30 00 00  0.000000  2    1.593749310156e-04  4.717165038980e-11
03  2009 01 30 00 00  0.000000  2    3.458468649886e-04  4.542246790350e-11
04  2009 01 30 00 00  0.000000  2   -3.176765824224e-04  2.733827659950e-11
05  2009 01 30 00 00  0.000000  2   -6.126657874204e-04  3.269050090460e-11

Can anyone help. Regards

Answer 1

google covers this ad nauseum. please use the phrases "file io" or "streams" in conjunction with "c++" or "cpp".

beyond that, if you have any more specific questions, you need to ask them.

Answer 2

Read the file line by line and replace "AS G" with an empty string. Common, it'll be more fun if you try to do it yourself (not mentioning that you'll learn much more this way).

For example code and the basics you need for this, look at this discussion and the documentation of string replace.

Answer 3

Do you NEED to use C++? If not, then Perl or any other similar tool/language would be a lot easier (and I'm a C++ developer)

Answer 4

Assuming you need to do this in C++ (awk would be easier) then you need to learn about iostreams.

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

int main()
{
  std::ifstream input("file.txt");
  std::stringstream sstr;
  std::string line;

  while(getline(input,line)) {
     if (line.length() > 4) {
         std::cout << line.substr(4);  // Print from the 4th character to the end.
     }
  }
}

By default getline reads the input until it gets end of line. You can also have it read input until it gets a specific character, eg space or comma with getline(stream,string,delimiter). In this way you can read a line a word at a time and process the individual values.

ps. When is SO going to get intellisense?

Answer 5

I prefer the answer by 'mgb' above.
But just for fun:

#include <fstream>
#include <iostream>
#include <iterator>
#include <algorithm>

struct Line
{
    std::string line;
};
std::ostream& operator<<(std::ostream& str,Line const& data) {return str << data.line << "\n";}
std::istream& operator>>(std::istream& str,Line&       data) {return std::getline(str,data.line);}

template<std::string::size_type Start>
struct ShortLine: public Line
{
    ShortLine(Line const& value)
    {
        // Note you need to check Start is in the correct rangs.
        line    = value.line.substr(std::min(Start,value.line.size()));
    }
};

int main()
{
    std::fstream    file("Plop");

    std::copy(  std::istream_iterator<Line>(file),
                std::istream_iterator<Line>(),
                std::ostream_iterator<ShortLine<4> >(std::cout)
            );

}