A seemingly simple problem (C/C++)

ErrorBound · 05-27-2006, 11:24 PM

Hi everyone,

I've written a program in C++ that takes a .csv (comma separated value) file as input and outputs a formatted table that LaTeX understands.

Anyway...it works as it is but requires the user to enter the number of columns in the .csv. The missing link is how to determine the number of columns in a table in this format. How could this be implemented? I imagine there must be something in one of the C or C++ standard libraries that could help me out?

All it needs to do is determine the number of columns in a file like this:

Code:

1,6,11
2,7,12
3,8,13
4,9,14
5,10,15

Here they are shown as integers but in general they could be floats or doubles.

Thanks for helping me out,

paulsm4 · 05-28-2006, 01:13 AM

What's wrong with a simple loop like this:

Code:

  int ncols = 0;
  ...
  << Open your CSV file >>
  while (fgets (buff, sizeof buff, fp) != NULL)
  {
    if (!ncols) 
    {
      for (int i=0; i < strlen (buff); i++)
      {
        if (buff[i] == ',')
          ncols++;  // Increment "ncols" for each comma
      }
      ncols++;  // #/columns = (#/commas + 1)
    }    
    ...
  }

Just a thought .. PSM

zhangmaike · 05-28-2006, 01:14 AM

EDIT: paulsm4 posted a split second before me... same suggestion. sorry.

read the first line
count the number of commas
add one

daihard · 05-28-2006, 03:52 AM

Not direct advice, but I'd wonder if you could make a simple shell script that does exactly that instead of resorting to writing a C++ program?

ErrorBound · 05-28-2006, 10:30 AM

Count the commas! Why didn't I think of that!!

paulsm4 && zhangmaike: Thanks for the suggestion, it works beautifully.

daihard: I'm sure you could, but I don't have any experience writing shell scripts and so I'm just using what I know.

daihard · 05-28-2006, 12:36 PM

Quote:

Originally Posted by ErrorBound

daihard: I'm sure you could, but I don't have any experience writing shell scripts and so I'm just using what I know.

Fair enough. I was in the same camp until very recently - knowing only C/C++ and not much shell scripting, so I know exactly what you mean.

paulsm4 · 05-28-2006, 01:44 PM

Here's one way to do it in a shell script:

Code:

head -1 myfile.csv|awk -F, '{print NF}'

"head -1 myfile.csv" lists only the first line in your CSV file. We pipe that line to "awk".

"-F," tells awk to separate fields using a comma (",") instead of a space or a tab.

NF is a built-in variable containing the #/fields in this line (i.e. #/columns in your file).

The output from your example would be "3".

Here's a good tutorial on bash scripting (one of many!):
http://www.freeos.com/guides/lsst/

Unfortunately, shell scripting isn't something you can "just learn" (by reading a book or a tutorial), because it's less about learning the syntax of a specific language ("bash" or "ksh") than it is about learning how to use all the different tools in the environment (sed, awk, cut, paste, etc etc) effectively.

Fortunately, getting started is easy (the basics are really simple), and gaining proficiency is fun (the more you play with it, the more you want to learn more).

IMHO .. PSM