C Program to read one line from another file

The Crab · 11-11-2011 11:06AM #1

Basically I have to make a guessing game where the answers and hints are stored in another file and the program reads them from there. However, before I even get halfway into it I want to be sure I'm storing the first string correctly.

When I put this code in I'm looking for it to read the first line, which will be the guess, but the code won't compile.

Not sure if it makes sense to write a little bit of my program first then try with the rest but if I don't get this then I can't see how I'll get the rest.

#include<stdio.h> 
int main()
{
FILE *fp, *fp1, *fprint;
int letter;
char fname[80];
char guess[80];
printf("Please enter the name of the file you wish to print: ");
gets(fname);
fp=fopen (fname, "r");
letter = fgetc(fp);
printf("The contents of the file <%s> are:\n", fname);
	while (letter != '\n')
	{
	fgets(guess, 80, fp1);
	letter=fgetc(fp);
	}

printf("%s", guess);
return 0;
}

It tells me permission is denied for the output file.

Colonel Panic · 11-11-2011 12:20PM

It makes sense to break things down as you said!

Looking at that code, it doesn't look like you've opened the fp1 file handle but you're calling fgets on it.

Plus, if you want to write to a file, you have to use the fputs funtion. How about trying to write to a file first, then adding the put to read from another file after?

The Crab · 11-11-2011 12:30PM

Colonel Panic wrote: »

It makes sense to break things down as you said!

Looking at that code, it doesn't look like you've opened the fp1 file handle but you're calling fgets on it.

Plus, if you want to write to a file, you have to use the fputs funtion. How about trying to write to a file first, then adding the put to read from another file after?

I don't need to write to a file. I've already done some of those in this assignment. I probably worded the question badly.

I'll have a look at the fp1 issue, thanks!

Colonel Panic · 11-11-2011 12:34PM

Ah I get it, you need to read a single line from the file!

If you're only dealing with one file, get rid of fp1 and fprint handles. It'll make your code more readable and it's good practice.

So yeah, if you change the fp1 in your while loop you'll make a bit more progress, but I think there's still a flaw in your logic but I'll leave that up to you to figure out for now!

The Crab · 11-11-2011 12:36PM

Colonel Panic wrote: »

Ah I get it, you need to read a single line from the file!

If you're only dealing with one file, get rid of fp1 and fprint handles. It'll make your code more readable and it's good practice.

So yeah, if you change the fp1 in your while loop you'll make a bit more progress, but I think there's still a flaw in your logic but I'll leave that up to you to figure out for now!

Is it that I have to do that stuff with converting chars to ints and so on??? Please please tell me that it isn't. I tried that last week and couldn't get my head around it.

Colonel Panic · 11-11-2011 12:39PM

No, it's not that.

When you call fgetc or fgets, you advance the position of the file stream. So by searching for an EOL character, you're not at the beginning of the file any more!

Also, there's an fscanf function that you could use too, but try it your way first!

The Crab · 11-11-2011 12:41PM

Colonel Panic wrote: »

No, it's not that.

When you call fgetc or fgets, you advance the position of the file stream. So by searching for an EOL character, you're not at the beginning of the file any more!

Also, there's an fscanf function that you could use too, but try it your way first!

Thanks, is my logic at least anyway right? I find C such a struggle...

Colonel Panic · 11-11-2011 12:58PM

C is pretty hard, but scanning through files like this and getting your head around it is fundamental stuff worth it. It's relevant regardless of language and something a lot of programmers these days don't know about!

Your logic is fine, but if you call these functions, you'll need to reset the file to read the first line.

The Crab · 11-11-2011 01:11PM

Colonel Panic wrote: »

C is pretty hard, but scanning through files like this and getting your head around it is fundamental stuff worth it. It's relevant regardless of language and something a lot of programmers these days don't know about!

Your logic is fine, but if you call these functions, you'll need to reset the file to read the first line.

How can I find out how to do that? I'm certain my lecturers didn't tell me.

Colonel Panic · 11-11-2011 01:22PM

The functions you're using are part of a C library called stdio.

Here is some documentation on it. Ignore the fact that it's on a C++ website, C++ is a not so strict superset of C.

C Program to read one line from another file

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