fscanf c programming

tomato · 01-05-2004, 05:34 PM

Hello.

I have just started to program in C.
I wonder why this code doesn't work.
I'm trying to read from a file

The text file looks like this:

Nevermind#Nirvana#1990
Freedom#Neil Young#1980

I'm trying to put the string "Nevermind" in the variable title and the string "Nirvana" in the variable artist and so on.

Code:

void importFile(char file[])
{
        FILE *stream;
        char title[50];
	char artist[50];
        char year[10];
		
	stream = fopen(file, "r");
	
	if(stream != NULL)
	{
	
	
		if(fscanf(stream,"%[^#]", title) != EOF)
			printf("\ntitle: %s", title);
		
		if(fscanf(stream,"%[^#]", artist ) != EOF)
			printf("\nartist: %s", artist);

		if(fscanf(stream,"%[^#]", year ) != EOF)
			printf("\nyear: %s", year);
	
		fclose(stream);
	}
	
}

The outout is:
title: Nevermind
artist: D@
year: D"½M@

Thanks

h/w · 01-05-2004, 08:19 PM

not a very helpful reply, but it obviously isnt matching anything after the first fscanf.

h/w · 01-05-2004, 08:30 PM

also, how do you know if stream is starting from where it left off?

codedv · 01-06-2004, 03:50 AM

The problem you are having is this.

fscanf(stream,"%[^#]", title) - This statement causes fscanf to read up to but not including the '#' character. That means that when fscanf stops reading characters the file pointer is placed on the '#' character.

In the next statement you do the same:
fscanf(stream,"%[^#]", artist);

However as the file pointer is already positioned on a '#' it doesn't read anything in.

The third statment is incorrect:
fscanf(stream,"%[^#]", year );

As there is no '#' character at the end of year - just a newline.

To cure this problem you need to read these characters off of the buffer. Heres some modified code:

Code:

#include <stdio.h>

void importFile(char file[])
{
        FILE *stream;

        char title[50];
        char artist[50];
        char year[10];

        stream = fopen(file, "r");

        if(stream != NULL)
        {
                /* the extra # will clear the # off the buffer */
                if(fscanf(stream,"%[^#]#", title) != EOF)
                        printf("\ntitle: %s", title);

                
                if(fscanf(stream,"%[^#]#", artist ) != EOF)
                        printf("\nartist: %s", artist);

                /*you can use %s here because fscanf stops reading when it
                  * hits a whitespace character
                  */
                if(fscanf(stream,"%s\n", year ) != EOF)
                        printf("\nyear: %s", year);

                fclose(stream);
        }
}

jtshaw · 01-07-2004, 09:06 AM

Or you could simply increment stream by 1 on successive reads:

Code:

if(fscanf(stream,"%[^#]", title) != EOF)
	printf("\ntitle: %s", title);
		
if(fscanf(stream+1,"%[^#]", artist ) != EOF)
	printf("\nartist: %s", artist);

And as the previous guy said, there is no # at the end so either search for a \n on the last read or put a # at the end of the year.

tomato · 01-07-2004, 11:12 AM

thanks, it works.

codedv · 01-09-2004, 12:09 PM

Quote:

Originally posted by jtshaw
Or you could simply increment stream by 1 on successive reads:

Code:

if(fscanf(stream,"%[^#]", title) != EOF) printf("\ntitle: %s", title); if(fscanf(stream+1,"%[^#]", artist ) != EOF) printf("\nartist: %s", artist);

And as the previous guy said, there is no # at the end so either search for a \n on the last read or put a # at the end of the year.

How does incrementing the file stream work?

If the file stream is a structure then surly incrementing it would be like incrementing an array

jtshaw · 01-09-2004, 12:11 PM

If I am not mistaken, stream is a pointer to the spot in the file you are currently at. Incrementing it would increment the pointer so you point to the next character in the stream.

Strike · 01-09-2004, 12:30 PM

Instead of blindly incrementing pointers that may get dereferenced later (segfault anyone?), you should just grab the separator character into a throwaway variable. I submit the following (untested) code as explanation of what I mean:

Code:

#include <stdio.h>

void importFile(char file[])
{
        FILE *stream;

        char title[50];
        char artist[50];
        char year[10];
        char separator = '';

        stream = fopen(file, "r");

        if(stream != NULL)
        {
                /* the extra # will clear the # off the buffer */
                if(fscanf(stream,"%[^#]", title) != EOF)
                        printf("\ntitle: %s", title);

                fscanf("#", separator);   /* Maybe check return value ?? */
                
                if(fscanf(stream,"%[^#]", artist ) != EOF)
                        printf("\nartist: %s", artist);

                fscanf("#", separator);   /* Maybe check return value ?? */

                /*you can use %s here because fscanf stops reading when it
                  * hits a whitespace character
                  */
                if(fscanf(stream,"%s\n", year ) != EOF)
                        printf("\nyear: %s", year);

                fclose(stream);
        }
}

You might even abstract out the separator into a #define so that you can easily make it something that's configurable later.

jtshaw · 01-09-2004, 02:09 PM

Ya, your right. Incrementing the pointer is a horrible idea. I was thinking to well apparently.

codedv · 01-09-2004, 02:21 PM

This:
fscanf(stream,"%[^#]#", artist);

Does the same as this:

fscanf("#", separator);
fscanf(stream,"%[^#]", artist);

itsme86 · 01-09-2004, 06:15 PM

Can't you just do:

fscanf(stream, "%s#%s#%s", artist, title, year);

?

h/w · 01-09-2004, 07:00 PM

i think that will go put whatever matches "%s#%s#%s" into artist?

itsme86 · 01-09-2004, 08:02 PM

I don't think so. Give it a shot.

Strike · 01-09-2004, 08:33 PM

Quote:

Originally posted by codedv
This:
fscanf(stream,"%[^#]#", artist);

Does the same as this:

fscanf("#", separator);
fscanf(stream,"%[^#]", artist);

You're right, the only advantage of separating them out would be evaluating the error conditions separately and I can't see how that would be helpful for this case.