Thread: file io help

>if(datain == NULL) {
It's usually easier to follow a program that tests for success first and then acts on failure. It also saves you the need to return early in the program.

Since you're simply taking a character from one file and placing it in another you would be better off opening both files at the same time and transferring the data like that.

>while (feof(datain)!= 0)
This is the incorrect use for feof. You don't want to use it as a loop condition for reading from a file. feof also returns a non zero if you have reached the end of file.

One very big problem with this program is that it won't work at all like you want because you open the input file, read until you reach the end, close the file, and then open the output file. The problem here is that you only have one character from the input file to print to the output file. Look over the following and see where the differences are. I didn't test my code, but I'm fairly confident that it will work.

Code:

#include <stdio.h>
#include <stdlib.h>

int main ( void )
{
  FILE *dataIn, *dataOut;
  int ch;
  if ( ( dataIn = fopen ( "datain.txt", "r" ) ) != NULL &&
     ( dataOut = fopen ( "dataout.txt", "w" ) ) != NULL )
  {
    while ( ( ch = fgetc ( dataIn ) ) != EOF )
      fputc ( toupper ( ch ), dataOut );
    fclose ( dataIn );
    fclose ( dataOut );
  }
  return EXIT_SUCCESS;
}

-Prelude

>it only does one letter though
Perhaps the first code, but the code I posted will handle any number of letters in a text file.

-Prelude