fseek - need some info please

I have read the boards, and It seems I am doing this right, but I am receiving garbage in my file:

I want to open a file, move to the 98th byte and write an email address:

Code:

---

define EMAILADDRLEN 90 // this is set above in the program
 
int e_loc = 98; // this is set above in the program
 
 
if ( (out = fopen("gorseve_10774.csv","w")) != NULL )
{
while ( (returnCode = fgets(lineOfText, LINESIZE, in )) != NULL)
{
  e_loc = parseGorseveRecord(lineOfText);
  printf("location found %d\n", e_loc);
  if ( (ret = fseek(out, e_loc, SEEK_CUR)) == 0 )
  {
    fwrite("[email protected]",sizeof("[email protected]"),EMAILADDRLEN,out);
  }
  else
  {
    printf("Error locating write position\n");
    exit(1);
  }
  fclose(out);
  exit(0);
  }
}
else
{
printf("Error Opening File: filename\n");
exit(1);
}

---

Quote:

---

Originally Posted by mhenderson

I want to open a file, move to the 98th byte and write an email address:

---

Your code does something else. First of all the position value is overwritten by

Code:

---

e_loc = parseGorseveRecord(lineOfText);

---

and then you use

Code:

---

fseek(out, e_loc, SEEK_CUR)

---

This moves e_loc bytes forward from the current position.
Kurt
EDIT sorry overlooked that read from a different file. But still the position is overwritten with another value.

should I be using fgetpos and fsetpos instead?

Thanks in advance !

sorry for that confusion,

that's what I meant by e_loc being set to 98 above, i just didn't want to copy in my parseGorseveRecord function. But I test the value of e_loc here:

printf("location found %d\n", e_loc);
This prints out 98.

Then the program exits.
When I check the file it has written over everything that was in it and just puts a 2 -3 lines of garbage?

The problem is the open mode "w" creates a new file. guess you want "a" ( but then you should use use SEEK_SET )
Kurt

Wow, I had that all wrong....

thank you so much!!

One more question :)

Once I've written that email address, is there an easy way to skip to the beginning of the next line ?

thanks in advance :))))

Quote:

---

Originally Posted by mhenderson

One more question :)

Once I've written that email address, is there an easy way to skip to the beginning of the next line ?

thanks in advance :))))

---

To find the next line you could open the file in read/write mode ("a+") and just read until you find a '\n'
On the othe hand combining textmode with fseek() is not a very good idea. try "rb+"
Kurt

> fwrite("[email protected]",sizeof("[email protected]"),EMAIL ADDRLEN,out);
This writes a hell of a lot more than you bargained for to the file.
Sizeof on a string constant is the number of chars in the string, and the \0 at the end.
And you write 90 copies of it!


In-place edits on text files isn't really the thing to do.

Read a line from the input file
Modify the line
Write the line to the output file.

When you're done, delete the old file and rename the new file.

yes, this sounds much better, if I use write ,will it just write an entire line over current line?

How do I go to the next line, and the next, etc.

Thanks again...I've been looking at this too long :)

You can only write to the end of a file opened in append mode. You'd be best off creating a new file as Salem suggested.

[edit] The thread is continued here: http://cboard.cprogramming.com/showthread.php?t=81559 [/edit]