L-33 MCS 275 Mon 2 Apr 2001

/* L-33 MCS 275 Mon 2 Apr 2001 : double spacing a file, graceful fopen */

#include <stdio.h>

void double_space ( FILE *ifp, FILE *ofp );
/* copies the content of the file ifp into the file ofp,
   duplicating every newline character */

void prn_info ( char *progname );
/* prints information on how to use the program */

FILE *open_input_file ( char *name );
/* tries to open the file with the given name for input;
   if failure, then the user will be asked to retry */

FILE *open_output_file ( char *name );
/* checks whether the file with the given name already exists;
   if the user gives not permission to overwrite, then a new
   file name is asked */

int main ( int argc, char **argv )
{
   FILE *ifp, *ofp;

   if (argc != 3)
   {
      prn_info(argv[0]);                /* print error message */
      exit(1);
   }
   else
   {
      ifp = open_input_file(argv[1]);   /* open for reading */
      ofp = open_output_file(argv[2]);  /* open for writing */
      double_space(ifp,ofp);            /* double newline symbols */
      fclose(ifp);                      /* close input file */
      fclose(ofp);                      /* close output file */
      return 0;
   }
}

void double_space ( FILE *ifp, FILE *ofp )
{
   int c;                               /* integer because of EOF symbol */

   while ((c = getc(ifp)) != EOF)
   {
      putc(c, ofp);
      if (c == '\n')
         putc('\n', ofp);               /* duplicate newline symbol */
   }
}

void prn_info ( char *progname )
{
   fprintf(stderr,"\n%s%s%s\n\n%s\n\n",
      "Usage : ", progname, " infile outfile",
      "Double-spaces content of infile into outfile.");
}


FILE *open_input_file ( char *name )
{
   FILE *infile;
   char work[80];                      /* work space for new names */

   strcpy(work,name);
   infile = fopen(work,"r");

   while (infile == NULL)
   {
      printf("%s\"%s\"%s\n",
         "File ", work,  " could not be opened.  Please try again...");
      printf("Give name of the input file : ");
      scanf("%s", work);
      infile = fopen(work,"r");
   }

   return infile;
}

FILE *open_output_file ( char *name )
{ 
   FILE *infile, *outfile;
   char newname[80];      
   char answer;

   infile = fopen(name,"r");            /* test whether file exists */

   if (infile == NULL)
      outfile = fopen(name,"w");
   else
   {
      printf("%s\"%s\"%s",
         "There is already a file ", name, ".  Overwrite ? (y/n) ");
      answer = getchar();
      if (answer == '\n')               /* skip leading new line symbol */
         answer = getchar();
      if (answer == 'y')
         outfile = fopen(name,"w");     /* overwrite existing file */
      else
      {
         printf("Give name of the output file : ");
         scanf("%s", newname);
         outfile = open_output_file(newname);    /* recursion */
      }
   }

   return outfile;
}