Question

So I’ve seen lots of solutions on this site and tutorials about reading in from a text file in C++, but have yet to figure out a solution to my problem. I’m new at C++ so I think I’m having trouble piecing together some of the documentation to make sense of it all.

What I am trying to do is read a text file numbers while ignoring comments in the file that are denoted by “#”. So an example file would look like:

#here is my comment
20 30 40 50
#this is my last comment
60 70 80 90

My code can read numbers fine when there aren’t any comments, but I don’t understand parsing the stream well enough to ignore the comments. Its kind of a hack solution right now.

/////////////////////// Read the file ///////////////////////
std::string line;
if (input_file.is_open())
{
    //While we can still read the file
    while (std::getline(input_file, line))
    {
        std::istringstream iss(line);
        float num; // The number in the line

        //while the iss is a number 
        while ((iss >> num))
        {
            //look at the number
        }
    }
}

else
{
    std::cout << "Unable to open file";
}
/////////////////////// done reading file /////////////////

Is there a way I can incorporate comment handling with this solution or do I need a different approach? Any advice would be great, thanks.

Answer 1

If your file contains # always in the first column, then just test, if the line starts with # like this:

while (std::getline(input_file, line))
{
    if (line[0] != "#" )
    {
        std::istringstream iss(line);
        float num; // The number in the line

        //while the iss is a number 
        while ((iss >> num))
        {
            //look at the number
        }
    }
}

It is wise though to trim the line of leading and trailing whitespaces, like shown here for example: Remove spaces from std::string in C++