Need help: File modification program in C

[paroshm]

Hi Folks

I need to modify a .txt file using a C program. The file contains name and phone number of my friends like below:

Mark 07915588623
Phill 07542535698
Claire 07825698745
...
...
.
.
...
If one of my friends phone number is changed (i.e. Claire 07985413791), how could I modify the file ucsing C codes?

[Narue]

This is a case where you can probably get away with overwriting rather than rewriting. Search for your friend's name, then step forward over the whitespace and simply write the new phone number:

/* Warning: this code was written without the aid of a compiler */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main ( int argc, char *argv[] )
{
  if  ( argc > 3 ) {
    FILE *stream = fopen ( argv[1], "r+" );
    char name[20];

    if  ( stream == NULL ) {
      perror ( "File open failure" );
      return EXIT_FAILURE;
    }

    while ( fscanf ( stream, "%s ", name ) == 1 ) {
      if ( strcmp ( name, argv[2] ) == 0 ) {
        long pos = ftell ( stream );

        /* Magic: switch to write mode */
        fseek ( stream, pos, SEEK_SET );
        fputs ( argv[3], stream );
        break;
      }
    }
  }

  return 0;
}

Of course you have a problem if you have more than one friend with the same name. Perhaps you should add last names to that file format. ;)

[Salem]

- fopen to open files, fclose to close them
- fgets / fputs to deal with whole lines
- sscanf to parse a line
- sprintf / strcpy / strcat / str.... to generally mess around with char arrays to arrive at the answer you want.

[paroshm]

Thanx Narue... but the code didnt work.
Thanx Salem....I need other friends' particulars unchanged.
How to do that?

[Narue]

>Thanx Narue... but the code didnt work.
I can't help you if you don't provide details. Do you take your car to the mechanic and say "It doesn't work"?

[Salem]

> How to do that?
Start with a program which COPIES the file unchanged.
Then add something like "I found Claire"
Then add something. I dunno, lets say prints the old and new phone numbers.

[paroshm]

Narue...I've the file name tel.txt. I executed the program like..
c:> parse.exe tel.txt Claire 07985413791

Then it says no such file or directory.

[Narue]

>Then it says no such file or directory.
Then your problem is user error. Make sure the file is in the current working directory when you run the program.