coding is not working

[deepak_kr_mehta]

THIS FOLLOWING CODE IS NOT WORKING

#include<iostream.h>
#include<conio.h>
int main()
{
char ch;
fstream file("m.txt",ios::in|ios::ate|ios::out);
file.seekg(0);
while(file.eof()==0)
{
file.get(ch);
if(ch=='h')
ch='i';
}
file.seekg(0);
while(file.eof()==0)
{
file.get(ch);
cout<<ch;
}
return 0;
}

this code is for replacing the characters in the file named "m.txt" but it is not working and not showing any error.
plz solve this query
from
deepak kr.

[redhead]

This is your problem

while(file.eof()==0)
{
file.get(ch);
if(ch=='h')
ch='i';
}

You identify the char correct, but once you've set ch to teh char you want to change it to, then you read past the point to place it.
A way of achieving it, would be to keep an array of positions, where the char was found, then in the end search through the file and replace the chars at the previus located postions.

Or you could simply replace it in the file, when ever you encounter it.
Something like this:

#include <iostream>
#include <fstream>

int main()
{
    char ch;
    fstream file("m.txt",ios::in|ios::ate|ios::out);
    file.seekg(0);
    while(file.eof()==0)
    {
        file.get(ch);
        if(ch=='h')
        {// seek back one char and replace it
            file.seekp(file.tellg() - sizeof(char));
            file << 'i';
        }
    }
    file.close();
    return 0;
}

Note: none of this code has been tested.

[Valmont]

Code like...

file.seekp(file.tellg() - sizeof(char));

...is not advisable, since the standard never guarantees proper conversion.
Also, after a read we want to reposition the write pointer. And after a write, we want to reposition the put pointer. Otherwise we end up with undefined behaviour.
Also...

while(file.eof()==0)

... we don't want to use eof() to decide whether file i/o should stop.
In general here is the code with comments:

#include <iostream>
#include <fstream>
#include <ios>

int main()
{
  //1) Open file in binary for more accurate positioning.
  //2) std::ios_base::ate is not needed.
  std::fstream file( "m.txt", std::ios_base::in |
    std::ios_base::out | std::ios_base::binary );
  //I initialize ch as well, just a neat thing to do.
  char ch( 0 );
  //Stream reader returns a value: acts like "false" if stream not good.
  while( file.get( ch ) )
  {
    if( 'c' == ch )
    {
      file.putback( ch );
      //Reposition put pointer after a read.
      file.tellp();
      file.put( '*' );
      //reposition get pointer after a write.
      file.tellg();
    }
  }
  return 0;
}