Thread: annoying file i/o

this has annoyed the hell out of me

Code:

if (!feof(fp)){
 fscanf(fp, "\n\n\n\n\n%s\n%s\n%s\n%s\n", line1, line2, line3, line4);
}

it keeps on reading the top line.is there a way to get it read down like this that will work.or why isnt this working?
thanks

Well, you could aways use fgets in a loop and read the lines like normal people...

Quzah.

>well is there a reason why this is not working?

yes

[edit]Also, you may have missed this:

FAQ > Explanations of... > Why it's bad to use feof() to control a loop

You just answered your own question. Use fgets. Seriously, what's the point of programming if you don't want to learn anything new or try any different way of doing things.

Quzah.

>i mentioned it for a hint to a link

Perhaps something akin to this.

I answered, with a link. But doesn't your compiler have any documentation? It's a standard library function. On MSVC, punch F1 and search. On *nix, type "man fgets" or "man 3 fgets".

Quzah.

I wrote my own function:

Code:

char *fget(char buf[], FILE *stream, size_t size) 
{
	int i = 0;
	while ((buf[i++] = fgetc(stream)) != EOF && i != size) 
		;;
	buf[i] = '\0';
	return buf;
}

Code:

buf[i] = '\0';

I'll assume that when you pass size to the function, it includes room for the null terminator right? Otherwise you're running past your array when this happens:

Code:

while ((buf[i++] = fgetc(stream)) != EOF && i != size)

But basicly, yours isn't reading a line, which is what the origional poster wanted. Yours just reads a number of bytes. Also, what's the point of returning the buffer, when you're passing and modifying the same buffer?

Quzah.

Originally Posted by quzah

Code:

buf[i] = '\0';

I'll assume that when you pass size to the function, it includes room for the null terminator right? Otherwise you're running past your array when this happens:

Code:

while ((buf[i++] = fgetc(stream)) != EOF && i != size)

[b]But basicly, yours isn't reading a line, which is what the origional poster wanted. Yours just reads a number of bytes. Also, what's the point of returning the buffer, when you're passing and modifying the same buffer?[b]

Quzah.

Yes, always! : )

I'm still learning! : )

Originally Posted by loopy

I wrote my own function:

Code:

char *fget(char buf[], FILE *stream, size_t size) 
{
	int i = 0;
	while ((buf[i++] = fgetc(stream)) != EOF && i != size) 
		;;
	buf[i] = '\0';
	return buf;
}

It looks fine, but it doesn't take care of the '\n'. It's not 'line oriented' like fgets() is.

Also, why ';;' ? I think '{}' is what you actually meant.

In fact, the code is buggy. The output expression should be ... && i < size - 1. If not, you'll stick the '\0' at buf[size] that is out of the bounds. It's an undefined behaviour.

Here is the FINAL version. ; )

Code:

int *fchar(char buf[], FILE *stream, size_t size)
{
	int i = 0;
	while ((buf[i++] = fgetc(stream)) != EOF && i < size -1)
		;;
	while (buf[i--] != '\n')
		;;
	buf[i] = '\0';
	return 0;
}

Called:

Code:

#include <string.h>
#include <stdio.h>
#include <unistd.h>
#include "/Source/str.h"

int main(int *argc, char *argv[])
{
	char buf[1024];
	int i = 0;
	FILE *file;
	if (!argv[1]) {
		fprintf(stdout, "Usage: File as first arg...\n");
		return 1;
	}	
	if ((file = fopen(argv[1], "r")) == NULL) {
		fprintf(stderr, "fopen: Failed.\n");
		exit(1);
	}
	fchar(buf, file, sizeof(buf));
	fprintf(stdout, "%s\n", buf);
	return 0;
}

In case anyone wants to play with it. ; )

{edit}

Changed it, I didn't notice anything strange.

Still lots of bugs in there
> while ((buf[i++] = fgetc(stream)) != EOF
You're comparing a char with EOF, not an int with EOF

> while (buf[i--] != '\n')
If you don't read a newline, then this marches off back towards the beginning of memory is a horrible buffer underrun.
Besides, it also means you lose a whole bunch of file data.

> #include "/Source/str.h"
Adding unistd.h made otherwise portable code less portable. What on earth is this for?