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Opening a File and Overwriting it Uppercase

Posted on 1998-07-22
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Last Modified: 2010-04-01
I am trying to get the following to work. I need to enter a filename, convert to uppercase,
and overwrite the same file:

#include <fstream.h>
#include <stdlib.h>
#include <ctype.h>


void runerror() { cerr << "Cannot open the specified file. Program was \
 terminated\n"; exit(1) ; }



int main(int argc, char *argv[])
{
    char fileName[100];

    if (argc !=2)
    { cout << "Incorrect usage of the program." << endl;
    cout << "Usage: " << argv[0] << " <filename>" << endl;
     return 1;
    }

    fstream tfile(argv[1], ios::in | ios::out);
    int i = 0;

      while (!tfile.eof())
            tfile.get(fileName[i++]);
      tfile.clear();
      for ( int j = 0; j < i; j++)
            tfile.put((char)toupper(fileName[j]));


return(0);
}

The above code appends the existing file.

What is missing?
0
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Question by:jnowlin
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9 Comments
 
LVL 8

Expert Comment

by:trestan
ID: 1168395
What's your problem? Your program works fine.

0
 
LVL 22

Expert Comment

by:nietod
ID: 1168396
What do you need to convert to uppercase?  the contents of the file?  if so open the file twice (that is, use  two different streams on the file).  Read a character from one stream, capitalize it, then write it back to the file with the other stream.
0
 
LVL 11

Expert Comment

by:alexo
ID: 1168397
trestan's answer is wrong.  You better reopen the question.

You need to set the write position to the beginning of the file.  Thus:

    tfile.clear();
    tfile.seekp(0, ios::beg); // <--- Add this line!!!
    for ( int j = 0; j < i; j++)
        tfile.put((char)toupper(fileName[j]));

0
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LVL 11

Expert Comment

by:alexo
ID: 1168398
One more thing, why do you read/write the constents of the file a character at a time?
It is much better to use the getline() method, or read() / write() methods or "<<" / ">>" operators to operate on buffers.
0
 
LVL 8

Expert Comment

by:trestan
ID: 1168399
I think your program does not work, but actually it works. You want to know why the converted string append on the end of the file while not overlap the original one? It is because after the read action, the pointer is at the end of the file. You should re-position it to the beginning of the file, like this:
while (!tfile.eof())
tfile.get(fileName[i++]);
tfile.clear();
tfile.seekp(0);//ios::beg);
for ( int j = 0; j < i; j++)
tfile.put((char)toupper(fileName[j]));
tfile.close();

You should close the file stream after you use it. As for the other options, I think it is up to you to use which of them. But if you have any questions, I would like to help you.
Sorry, I did not see that alexo already give the answer.
0
 
LVL 11

Expert Comment

by:alexo
ID: 1168400
>> Sorry, I did not see that alexo already give the answer.
I guess I must start using a bigger font.
0
 

Author Comment

by:jnowlin
ID: 1168401
I guess I'm re-opening this question for Alexo. Thanks very much to everybody!

Jim Nowlin
0
 
LVL 2

Expert Comment

by:duneram
ID: 1168402
you may wish to use the strupr function as well.  that function will convert a string to uppercase for you, not just a character at a time
0
 
LVL 11

Accepted Solution

by:
alexo earned 60 total points
ID: 1168403
tfile.seekp(0, ios::beg);

Have fun!
0

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