Thread: program that reads several files & writes concatenated contents into file

I'm not really sure what this is asking me to do. Please help!
DUE at 9pm and I have no clue what to do.
I'll keep working on what I have though..
(see at end of post)


In this quiz you will write a program (quiz4.c) that sequentially
reads several files and writes their concatenated contents into
another file. The names of the files to be read and the file to
write to will be specified on the command line. For example, after
you compile your code and run:

iacs5.ucsd.edu% ./a.out quiz3.c quiz4.c output

the file output should contain the concatenated contents of both
quiz3.c and quiz4.c. The last parameter is always the name of the
file where you write to (destination file) whereas all other
parameters are the names of the files you read and concatenate in
the order they appear. Your program should perform the following
checks:

a) If less than two parameters are passed to the program, abort with
an error message (at a minimum there should be one file to read
and the destination file);

b) If a you cannot open the destination file for writing, abort with
an error message;

c) If you cannot open any of the files to be read issue a warning
message and continue to the next file. If this is the last file
then simply close the destination file and exit your program
without further messages.

You must use fgets in order to read files and fprintf to write to
the destination file. Take a look at program w6-5.c to see how fgets
works and program w5-8 to see how to retrieve command line
arguments.

HINT: You can use the unix commands cat and diff to check your
program. If you run

iacs5.ucsd.edu% ./a.out quiz3.c quiz4.c output.1
iacs5.ucsd.edu% cat quiz3.c quiz4.c > output.2

then the command

iacs5.ucsd.edu% diff output.1 output.2

should produce no output if you have done your job right. Otherwise
you will see a number of complaints about differences in the two
files.


quiz3.c & quiz4.c are just examples. In practice, any files you input should work (as long as the files exist).

Here's what I have so far:
I don't know if i'm anywhere close to the right answer..

Code:

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define FILEMAX 1000000

FILE *fp;

main ()
{
	
for(i=1; i<3; i++)
{
printf("Input filename:");
fscanf("%s",filename);
fp=fopen(filename, "a");
	if(fp==NULL)
	{
		printf("ERROR\n");
	}
		exit(1);
}

Thank you!!

do you know anything about argc and argv[ ] ? you MUST use them...

This would work with some modification: File IO - Rosetta Code

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Category:Programming Tasks - Rosetta Code
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My C Stuff (GPL):
PaperDragon
TML Version 2
Fix missing brackets with Anchor
The Nerd Show | Platypus

look...

argc is the number of arguments you give after a.out. so, if you type a.out 2 4 56 5 argc will be 5 got it? now, argv is something like an array...imagine that in the first cell you "a.out" in the second the number 2 in the third the numer 4 etc...does this helps a little?

It is definitely starting to make more sense and the examples help.
Thank you both so much!!

I think I understand argc but I'm still a bit confused about argv.
Also, how would I get the program to prompt the user for file names?
I think this involves fgets and fscanf (and fprintf for the final file) but I'm not completely sure how to go about writing this.

I do remember reading something about printing arguments backwards but I don't know how I would use it for this particular program.

Thank you again!

when working with files you definitely use fscanf, fprintf etc...actually this functions are made for this reason...

Now let me show you an example about argv[ ]...

Code:

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

int main(int argc, char *argv[]){
	printf("argc: %d\n", argc);
	printf("argv[0]: %s\n", argv[0]); 
	printf("argv[1]: %s\n", argv[1]); 
	printf("argv[2]: %s\n", argv[2]); 
return 0;
}

Originally Posted by sam...

It is definitely starting to make more sense and the examples help.
Thank you both so much!!

I think I understand argc but I'm still a bit confused about argv.
Also, how would I get the program to prompt the user for file names?
I think this involves fgets and fscanf (and fprintf for the final file) but I'm not completely sure how to go about writing this.

I do remember reading something about printing arguments backwards but I don't know how I would use it for this particular program.

Thank you again!

Are you reading different assignment instructions than what you posted, sam? This one said to use command line arguments, not prompt for file names.

a) If less than two parameters are passed to the program, abort with
an error message (at a minimum there should be one file to read
and the destination file);

Code:

/* your program name will be 1, so you need two more files, for 3, minimum */
if argc < 3  
  print"Two file minimum is required - terminating\n"
  exit(1)
end if

b) If a you cannot open the destination file for writing, abort with
an error message;

Code:

char filename[80];
FILE *fp;

fp equals fopen(argv[argc], "a")
if fp == NULL
  print "Error opening output file - terminating\n"
  exit(1)
end if

c) If you cannot open any of the files to be read issue a warning
message and continue to the next file. If this is the last file
then simply close the destination file and exit your program
without further messages.

Code:

for i equals 1; i less than argc; i++
  fp equals fopen(argv[i], "r")

  if fp is NULL && i less than argc - 2  //
    print "Warning: An input file failed to open - continuing
  end if

etc.

Just tick them off, one after the other. Meter by meter, life is sweeter.

Your code should have no "Enter filename" stuff, in it. That is being handled via argc and *argv[], for you.

I was wondering...
You haven't used "fprintf" or "fgets". Will it still work?

Originally Posted by Adak

Code:

/* your program name will be 1, so you need two more files, for 3, minimum */
if argc < 3  
  print"Two file minimum is required - terminating\n"
  exit(1)
end if

Code:

char filename[80];
FILE *fp;

fp equals fopen(argv[argc], "a")
if fp == NULL
  print "Error opening output file - terminating\n"
  exit(1)
end if

Code:

for i equals 1; i less than argc; i++
  fp equals fopen(argv[i], "r")

  if fp is NULL && i less than argc - 2  //
    print "Warning: An input file failed to open - continuing
  end if

etc.

Just tick them off, one after the other. Meter by meter, life is sweeter.

Your code should have no "Enter filename" stuff, in it. That is being handled via argc and *argv[], for you.

Here is a similar snippet, written in Anchor script. Anchor is C (but punctuation is sort of optional).
Stuff like this actually compiles with it
Anchor | freshmeat.net

Error checking and usage information would go after the closing brackets, of course...

Code:

    /* argc is always 1 more than what we need... */
    argc--
    /* is the number of files correct? */
    if  argc > 2
        /* yes, can we open last file for append in binary mode? */
        if  (f_out=fopen(argv[argc],"ab+"))
            /* yes, let's iterate through each file */
            for  this_file=1; this_file < argc; this_file++
                /* can the file can be opened for reading? */
                if  (f_in=fopen(argv[this_file],"rb"))
                    /* yes, read all of f_in and append to f_out */
                    while  fgets(buf,buf_MAX,f_in)
                        fprintf  f_out,"%s",buf
    return 0

another example...i believe it compiles...

Code:

#include <stdio.h>

int main(void){

     FILE *infile, *outfile;

     int c;

     char buf[10];

     

     if((infile=fopen("lala.txt", "r"))==NULL){

          exit(1);

     }   

     while(fgets(buf, 10, infile) != NULL){

          fputs(buf, outfile);

     }

     fclose(infile);

     fclose(outfile);

return 0;

}

Hmm. Actually the directions say at minimum 1 input and 1 output file, so my > 2 was too much. Oh well. Not going to be a perfectionist.