Thread: 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); 
}

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.

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

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]