Re: C++ programming: keeping count of data items read from file

[Mark Allums <mark@allums.com>]

H.S. wrote:
> Hello,
>
> In a C++ program I am reading a data file for later processing and 
> computations. While reading that data file, I want to keep track of data 
> items (doubles) read.
>
> The data file is just a text file with N lines with C doubles in each 
> line (N and C are known a priori). For now, I just read from the file 
> stream in to a 2D array variable by reading each double at a time.
>
> Now I am trying to introduce some sanity checking into this reading 
> block. Here is what I am trying to do:
> 1. Verify how many doubles I have read in each line. Must be C. If they 
> are not C, then the input file is corrupt.
> 2. Verify that the total number of data items are NxC. This is simple, I 
> just keep a track of how many numbers I have read.
>
> So, how do I go about doing (1) above? I was thinking of somehow 
> checking if I have reached the end of line somehow (EOL?) but haven't 
> found a method to do so. All I have found is EOF.
>
> thanks,
> ->HS

Not directly helpful, but some suggestions:

1. You might want to learn PERL or Python or Ruby, and do it there.
2. If it has to be C++, learn enough PERL to write a filter for the data 
file, and transform it so that it has one double per line.
3. Debug the data generator /in situ/ with a good debugger, and bypass 
the need to do the sanity checking.
4. Find a good C++ reference, and use it.  There are several.

Slightly more helpful:

1. Read one line at a time in as a string, then operate on the string.
2. C++ has the ability to do everything that C does in a low level way, 
but why?  Use the C++ way, or use the C way:

#include <cstdio>
#include <iostream>
. . .
using namespace std;
. . .
ios::sync_with stdio();
. . .
int blah = fscanf(somefile,"%f %f %f %f\n", d1,d2,d3,d4);
if (blah != correctvalue)
 {
    dosomething();
    closefiles();
    cout << "error in data file\n";
    exit(1);
 }
. . .
// etc.


(The ios::sync_with_stdio(); line may differ slightly on different C++ 
implementations.  I haven't used it in a while.  May be spelled synch_. 
 Too lazy to look it up.

The fscanf line may just be wrong. I quit writing C programs years ago. 
 Too old, memory failing.)



--
Mark Allums