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Urgent/Strange  fstream & binary file

Posted on 1998-07-13
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Last Modified: 2010-04-01
I have a very strange problem with fstream & binary file
( see the program added )
Every time i write the number 26 to the binary file
the program treats it like an EOF & exist.



#include <fstream.h>


fstream      g_File3;

void main()
{
      int xx, yy, i1;

      g_File3.open("c:\\Temp\\DD_UT.dat", ios::out);

      xx = 26;
      g_File3.write((unsigned char *)&xx, sizeof(int));
      g_File3.write((unsigned char *)&xx, sizeof(int));
      g_File3.write((unsigned char *)&xx, sizeof(int));
      
      g_File3.close();

      g_File3.open("c:\\Temp\\DD_UT.dat", ios::in);

      for (i1 = 0; i1 < 3; i1++)
      {
            
            yy = 0;
            g_File3.read((unsigned char *)&yy, 4);
            cout << g_File3.gcount() << endl << flush;
            if (g_File3.eof() == 1)
            {
                  break;
            }

      }

}


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Question by:sector
  • 3
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5 Comments
 
LVL 22

Accepted Solution

by:
nietod earned 100 total points
ID: 1167636
a 26 is a control-Z.  In the olden days of DOS, a control-Z was used to mark the end of a text file.  Apparently you are running into that.
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LVL 22

Expert Comment

by:nietod
ID: 1167637
I suppect the problem lies in the fact that you have opened the file in text mode  (you say in the question title that it is binary mode, but the example shows it is opened in text mode.)  top open it in binary mode use

g_File3.open("c:\\Temp\\DD_UT.dat", ios::in | ios:binary);

I hope this helps.  Let me know if not.
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LVL 8

Expert Comment

by:trestan
ID: 1167638
Sorry, but I want to say that Mr. nietod's proposal can not overcome the problem. I have compiled the codes by myself and found that the problem is the data conversion. In the original code, the int type is casted to char by explicit type cast. But the result is meaningless to do it in this way. The correct method is to use Data Conversion routine. In this case, _itoa can be used like this:
char * xxc;
_itoa (xx, xxc, 10);

save xxc to the file instead of xx.

ilanmoshe, if you find the later answer is the right solution, pls do not forget to reject the original one so that the person who provide the right one can get the points.
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LVL 8

Expert Comment

by:trestan
ID: 1167639
By the way, do you have some special reason that you do not use << and >> operators?
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LVL 22

Expert Comment

by:nietod
ID: 1167640
>> In the original code, the int type is casted to char by explicit type cast

No, a POINTER to an int is cast to a POINTER to a char.  This is standard practice in binary read/write operations.  Also _itoa() converts the data to ASCII, but the point is to write it in binary, not ASCII.
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