I/O array problem with data files

Mr_Peepers · #1 19-Feb-2008, 21:12

Currently I need to read data from a file, such like this

Measurements for Lansing, Michigan during April, 2000
63 32 0.00
54 43 0.10
59 39 0.00
46 24 0.00
52 20 0.00
54 30 0.00

The first line is obviously disregarded, since all we want are the numbers.

limitations are simply use arrays, no vectors.

I had something like this for now, though I'm not sure if it cuts the first line out or not...I'm also cutting main() off the post, I know it works, its the I/O I don't get.

CPP / C++ / C Code:

      void read( ifstream& In, ReadData List[], int Size, int& Num )
      {
        ReadData Temp;
 
        Num = 1;
       
        for (;;)
        {
          In >> Temp.Min >> Temp.Max >> Temp.Precipt;
       
          if (In.fail() || Num >= Size) break;
       
          List[Num] = Temp
       
          Num++;
        }
      }
 
      void process( const ReadData List[], int Num )
      {
        int I;
        //***************************
        // Display the column headers
        //***************************
       
        cout << "\n";
        cout << "Minimum Value      Maximum Value     Precipitation\n";
        cout << "-------------      -------------     -------------\n";
       
        for(I=0;I<Num;I++)
        {
          cout << resetiosflags( ios::right ) << setiosflags( ios::left );
          cout << setw(20) << List[i].Min << "          "<< List[i].Max << "          "<< List[i].Precipt <<endl;
        }
      }

declaring the struct is

CPP / C++ / C Code:

      struct ReadData
      {
        int Min,Max;
        double Precipt;
      };

Currently the output yeilds
0 0 (some reference address)

...and thats it

I know i'm somewhere close, but I'm drawing a blank. I set Num = 1 in hopes of skipping the first set in the data, which would be the string of words

How do i fix the array so it yields the correct I/O?

Your help is greatly appreciated

WaltP · #2 19-Feb-2008, 22:06

To skip the first line of the data file, use getline().

Then, always display what was read immediately after reading it to make sure the read worked properly.

#3 20-Feb-2008, 06:26

Quote:

Originally Posted by WaltP

Then, always display what was read immediately after reading it to make sure the read worked properly.

Mr_Peepers, you'll note that WaltP is absolutely fascinated with printf/cout...

If you use the C++ streaming library functions properly, you don't need couts littering your code. All you have to do is check that the ios::good bit is set after a read. That means that "the read worked properly."

Here's a simple example:

CPP / C++ / C Code:

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main()
{
    cout << "Enter the filename containing data to be read: ";
    string filename;
    getline( cin, filename );
    ifstream infile( filename.c_str() );
    if( infile.is_open() )
    {
        int x;
        while( infile.good() )
        {
            infile >> x;
            if( infile.good() )
            {
                cout << "Read " << x << endl;
            }
            else
            {
                if( infile.fail() )
                {
                    cout << "fail flag set" << endl;
                }
                if( infile.eof() )
                {
                    cout << "eof flag set" << endl;
                }
                if( infile.bad() )
                {
                    cout << "bad flag set" << endl;
                }
                cout << "Error reading from stream opened on file named " << filename << endl;
            }
        }
        infile.close();
    }
    return 0;
}

Output:

Code:

Enter the filename containing data to be read: /tmp/foo.txt
Read 1
Read 2
Read 3
fail flag set
Error reading from stream opened on file named /tmp/foo.txt

$ cat /tmp/foo.txt
1 2 3 ABC

Note how the contents of foo are organized. The read tries to convert to an integer in the loop. Since the first three conversions are successful, the output is as expected and "x" is "happy" each time through. When the input stream encounters data that can not be converted to "x," we get a fail bit set.

Here's the code that does the work that you want to do, without a bunch of silly "displays" of the read activities...always is a fairly hefty requirement, huh?!

Of course, I didn't use an array, but I didn't use a vector, either. I used dynamic memory allocation and a series of linked data structures in a very abbreviated "linked list" fashion.

CPP / C++ / C Code:

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

typedef struct st_data
{
    int             x;
    int             y;
    float           f;
    struct st_data* next;
} DATA;

int main()
{
    DATA* p_data    = new DATA();
    DATA* p_tmp     = NULL;
    DATA data;
    unsigned int ui = 0;

    cout << "Enter the filename containing data to be read: ";
    string filename;
    getline( cin, filename );
    ifstream infile( filename.c_str() );
    if( infile.is_open() )
    {
        getline( infile, filename ); // skip the first line
        while( infile.good() )
        {
            infile >> data.x >> data.y >> data.f;
            if( infile.good() )
            {
                ++ui;
                p_tmp = p_data;
                if( ui != 1 ) // not at list head node
                {
                    while( p_tmp->next != NULL ) // get to the end of the list
                    {
                        p_tmp = p_tmp->next;
                    }
                    p_tmp->next = new DATA(); // add a new node
                    p_tmp->next->x = data.x; // copy the data
                    p_tmp->next->y = data.y;
                    p_tmp->next->f = data.f;
                    p_tmp->next->next = NULL;
                }
                else
                {
                    p_tmp->x = data.x;
                    p_tmp->y = data.y;
                    p_tmp->f = data.f;
                    p_tmp->next = NULL;
                }
            }
        }
        infile.close();
        cout << "Read " << ui << " data chunks " << endl; // user feedback
    }

    if( ui > 0 ) // print the data
    {
        p_tmp = p_data;
        while( p_tmp != NULL )
        {
            cout << p_tmp->x << " " << p_tmp->y << " " << p_tmp->f << endl;
            p_tmp = p_tmp->next;
        }
    }

    while( p_data->next != NULL )
    {
        p_tmp = p_data->next;
        delete p_data;
        p_data = p_tmp;
    }
    delete p_data;

    return 0;
}

Output:

Code:

Enter the filename containing data to be read: /tmp/data.txt
Read 6 data chunks
63 32 0
54 43 0.1
59 39 0
46 24 0
52 20 0
54 30 0

Code:

==4626== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 16 from 1)
--4626--
--4626-- supp:   16 Ubuntu-stripped-ld.so
==4626== malloc/free: in use at exit: 0 bytes in 0 blocks.
==4626== malloc/free: 20 allocs, 20 frees, 9,072 bytes allocated.
==4626==
==4626== All heap blocks were freed -- no leaks are possible.

...you may want to add iomanip to your include directives.

Also, if you add lines to your data file (I copied the same data and pasted it several times in the file to "grow" it significantly):

Code:

Enter the filename containing data to be read: /tmp/data.txt
Read 2184 data chunks
63 32 0
54 43 0.1
59 39 0
46 24 0

...the code should continue to work.

Code:

==4865== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 16 from 1)
--4865--
--4865-- supp:   16 Ubuntu-stripped-ld.so
==4865== malloc/free: in use at exit: 0 bytes in 0 blocks.
==4865== malloc/free: 4,376 allocs, 4,376 frees, 141,930 bytes allocated.
==4865==
==4865== All heap blocks were freed -- no leaks are possible.

...of course, once you run out of memory, the code will fail and the "leak" will not be cleaned up. But that's another topic...

:davis:

Mr_Peepers · #4 20-Feb-2008, 14:23

Thanks Davis, That really seemed to help fix reading and outputting.

I should have mentioned, with that data, some things need to be calculated, namely average x, y, and z values, and simple searches to find the smallest and largest numbers.

So with this allocation method, average for x would go something like this?

CPP / C++ / C Code:

while ( p_tmp != NULL )
  {
    total += p_tmp-> x;
    count += 1;
    p_tmp = p_tmp -> next;
  }

having of course declared total and count, with average being total / count.

WaltP · #5 20-Feb-2008, 17:03

Quote:

Originally Posted by davis

Mr_Peepers, you'll note that WaltP is absolutely fascinated with printf/cout...

And Dave has never mentioned them. Hmmm....

#6 21-Feb-2008, 07:51

Quote:

Originally Posted by WaltP

And Dave has never mentioned them. Hmmm....

Spoken like a true, self-proclaimed expert with over 30 years of programming experience...that is, accept no responsibility for what you post. Redirect away from yourself. Completely discount that you said "always" because Dave has "never not" mentioned using printf/cout.

Why not celebrate an option to using printf/cout?! Do you feel that their presence in your own code really help you more than hurt you? How many times have you needlessly typed printf or cout followed by some string constants and data members? That time couldn't be better utilized? How many hours over the supposedly 30+ years might you have saved by employing alternatives that also "live well" in "release" code? How much time did you spend taking OUT the spew to console statements? How much time did you waste putting them in the WRONG places? Hey, you're the expert. Who are the rest of us simpletons to be suggesting that you are not the commander of your own destiny and that we mere mortals should grovel at every opportunity to partake in the blessings of coding prophecy offered by the truly Outstanding Member (graded solely on quantity, not quality) found in the glorious visionage encountered here as WaltP?

How long ago was it that you were some kind of prince entering some buildings and your fairy tale wonderland of C++ was a dark place where, with a little C knowledge, you could somehow "see" your way around a bit?

Remember how that started? Gather 'round children, and I'll tell you a story.

...you somehow promote yourself to "adult" status and everyone else to "children." Who was the "young prince?" By your story, he was well-versed in the art of C...that seems to imply that you meant yourself.

Maybe you are the product of an environment where many, many novices come, but you are somehow an "expert" because of your modestly advanced skill compared to them? It sounds to me as if you're believing your own fairy tales...

:davis:

#7 21-Feb-2008, 07:59

Quote: