Thread: Need Help Fixing My C Program. Deals with File I/O

My program is supposed read in a file supplied from the commandline (filename.ext,) and write/overwrite out a file.

This file will be essentially the same as the original file, but will have all characters on all lines the reverse of the original. For example:
The original file has:
Jack Spratt
could eat no fat.

The output file will look like:

ttartpS kcaJ
.taf on tae dluoc

The approach i decided to take was to read the input file, creat a temporary file, and then reverse it there, later toss the reverse d strings into the output file, but somehow its not working, i believe it has something to do with my reverse function, can anyone help fix it? I also get these errors:

C:\Documents and Settings\Administrator\My Documents\100_php_scripts\myown.c In function `main':

28 C:\Documents and Settings\Administrator\My Documents\100_php_scripts\myown.c [Warning] passing arg 1 of `reverse' makes pointer from integer without a cast


here are the codes i have!

Code:

#include <stdio.h>


void reverse( char *sPtr ); // function to revers the characters from input to output

int main (void)
{
    FILE *fileinput; //pointer to file being modified
    FILE *temp;//temporary file pointer
    FILE *fileoutput;//pointer to where contents will be written
    int c;//hold characters from input file
    char filename [30]; //file name create char array
    
    printf("This program reverses your text file.\n");
    printf("Enter a File to be modified:\n" );
    scanf("%29s",filename);
    
    //opens input file
    if ((fileinput = fopen (filename, "r")) != NULL){ 

       //creates temporary file
       if ((temp = tmpfile()) != NULL) {
          printf("\nThe File before modification is:\n");
          
             //read characters from file and place in temporary file
             while((c= getc(fileinput)) != EOF) {
                putchar (c);
                (temp,reverse(c)); 
                 }//end while
                
                rewind (temp);
                rewind(fileinput);
                
                printf("\n\n The File after modification i:\n");
                
                //read from temporary file and write to output file
                while ((c = getc(temp)) != EOF) {
                   putchar(c);
                   putc(c,fileoutput);
                   }// end while
                   
                   }//end if
                   
                   else{ // if temporary file could not be opened
                      printf("unable to open temporary file\n");
                      }//end else
                      
                           }           //end if

                else {//if input file could not be opened
                     printf("Unable to open %s\n",filename);
                }//end else
                
    fclose (fileoutput);            
    fclose(fileinput);
    fclose(temp);
   
    return 0;
}
                
void reverse(char * sPtr ) // reverse function
{
   if( sPtr[ 0 ] == '\0' ){
      return;
   }
      else{
         reverse( &sPtr[ 1 ] );

         putchar( sPtr[ 0 ] );
     }
} // end function

I wonder what you think "(temp, reverse(c))" does. Note that reverse needs the entire line of input, not just one character at a time.

Hmm ya, i figured im only sending it one character while it needs a string. I tried using fgets and fscanf, but still i get a bunch of errors. What approach would u take in solving this problem.

Originally Posted by Matus

I tried using fgets and fscanf, but still i get a bunch of errors.

Then you didn't try hard enough. You need to work one line at a time, so you need to read one line at a time, and fgets is the main line-based input function. You do need to make sure you have a char array handy to put the input into.

Originally Posted by tabstop

Then you didn't try hard enough. You need to work one line at a time, so you need to read one line at a time, and fgets is the main line-based input function. You do need to make sure you have a char array handy to put the input into.

ahh i see its like something on what i was working with at the begining, i had something very close to what u were talking about when i started working with the program. Can you check out the one i worked with at first, i know its practically finished, if i could get that to run properly i can have the one above working in no time. i get these errors with the codes below:

C:\Documents and Settings\Administrator\My Documents\100_php_scripts\Untitled1.c In function `flipstring':
68 C:\Documents and Settings\Administrator\My Documents\100_php_scripts\Untitled1.c [Warning] function returns address of local variable

These are the codes: Sorry i know indentation is crappy on this one.

Code:

#include <stdio.h> 
    #include <string.h> 
  
    #include <ctype.h>  
      
    // Our function declaration saying it takes one string pointer and  returns one string pointer.  
char * flipstring(char *stringtoflip);  
   
 int main() {  
  //  Strings to hold our lines (forward and backward)  
  char  string[256];  
  char flipped[256];  
   
  //  Our file pointers (one in and one out)  
  FILE * infile;  
  FILE * outfile;  
   
  // Open files to valid  txt files  
  infile = fopen("input.txt","r");  
   
 outfile = fopen("output.txt","w");  
   
  // Loop  through the input file reading each line up to 256 chars  
   
 while (fgets(string,256,infile) != NULL) {  
  printf("The  value read in is: %s\n", string);  
   
  // Flip the  string and copy it to our "flipped" string  
   
 strcpy(flipped,flipstring(string));  
   
  // Write  "flipped" to output  
  printf("The value written is:  %s\n",flipped);  
  fputs(flipped,outfile);}  
   
  // Close files  
  fclose(infile);  
  fclose(outfile);  
   
  return 0;  
 }  
    
 // Flips strings by taking incoming   string, loop in reverse  
  // and write each char to reverse  string. Return reverse string.  
  char * flipstring(char *stringtoflip) {  
   char reverse[256];  
    
    
  int j = 0;  
  int i= strlen(stringtoflip)-1;
    
   // Loop through each char of our  string in reverse  
   for( i ;i>=0; i--)  
   {  
   // If it is a newline, just  ignore for now.  
   if (stringtoflip[i] != '\n') {  
    
  reverse[j]=stringtoflip[i];  
   j++;  
   }  
    
  }  
   
   // Terminate the new reverse string.  
   reverse[j] = '\0';  
    
   // Return reverse  string back to main()  
    return reverse;  
 }

The error is just what it says: you are returning the address of a local variable; but once the function has ended (and the address returned) the local variable ceases to exist, which means you are pointing at nothing in particular. Pass in the array to hold the flipped value instead.

Originally Posted by tabstop

The error is just what it says: you are returning the address of a local variable; but once the function has ended (and the address returned) the local variable ceases to exist, which means you are pointing at nothing in particular. Pass in the array to hold the flipped value instead.

How could i fix that, i tried declaring it as a static variable but still nothing, can you help me out

Originally Posted by Matus

How could i fix that, i tried declaring it as a static variable but still nothing, can you help me out

I suggest reading:

Originally Posted by tabstop

Pass in the array to hold the flipped value instead.