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Opening a File and Overwriting it Uppercase

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
jnowlin
Asked:
jnowlin
1 Solution
 
trestanCommented:
What's your problem? Your program works fine.

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nietodCommented:
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.
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alexoCommented:
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]));

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alexoCommented:
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.
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trestanCommented:
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.
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alexoCommented:
>> Sorry, I did not see that alexo already give the answer.
I guess I must start using a bigger font.
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jnowlinAuthor Commented:
I guess I'm re-opening this question for Alexo. Thanks very much to everybody!

Jim Nowlin
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duneramCommented:
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
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alexoCommented:
tfile.seekp(0, ios::beg);

Have fun!
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