Opening files for reading and writing

We can now create a program to open a file for reading and another file for writing. This is where our file I/O exploration will begin and continue through the remaining chapters of this book. The following program is our starting point:

#include <stdio.h>

#include <stdlib.h>     // for exit()

#include <string.h>     // for strerror()

#include <sys/errno.h>  // for errno

int main( void ) {

  FILE* inputFile;

  FILE* outputFile;

  char inputFilename[] = "./input.data";

  char outputFilename[] = "./output.data";

  inputFile = fopen( inputFilename , "r" );

  if( NULL == inputFile )  {

    fprintf( stderr, "input file: %s: %s\n", 

     ...