Extracting Information from Files

**Pztar** · 05-24-2011

Hello,

What is the best, and easiest way to extract information from Files?

For example:

I open afile.txt

afile.txt contains:

/*
City Distance1 Distance2 AvgDistance

Miami 50 60
Montreal 90 65
Vancouver 87 63

*/

In that exact spacing. How can I extract the strings and numbers and use it?
I know it's a simple solution, but I can't seem to work it out. I don't mind if it I have to store each into it's own variable. As long as you can explain your answer, it would HELP a lot more than just posting a solution.

Thanks

**quzah** · 05-24-2011

Do the same thing this guy needs to do: NEED GUIDANCE: Loading String from a .txt/.dat file into Arrays

Quzah.

**~~CommonTater~~** · 05-25-2011

Originally Posted by Pztar

Hello,

What is the best, and easiest way to extract information from Files?

For example:

I open afile.txt

afile.txt contains:

/*
City Distance1 Distance2 AvgDistance

Miami 50 60
Montreal 90 65
Vancouver 87 63

*/

In that exact spacing. How can I extract the strings and numbers and use it?
I know it's a simple solution, but I can't seem to work it out. I don't mind if it I have to store each into it's own variable. As long as you can explain your answer, it would HELP a lot more than just posting a solution.

Thanks

Take a look at the two functions fgets() and sscanf() in your C library documentation.

**Pztar** · 05-25-2011

I still don't know how to do it. I retrieve the information with fgets() that works fine for me.

But I can't get the information that I want with sscanf(). I'm not sure how to do it..

I've searched google, and I can't find what I'm looking for. I found something where the example used a sentence and that seems simple. But I don't know how to apply it to my situation.

I know I may be asking too much, but I just want to learn how to do it.

**tabstop** · 05-25-2011

sscanf works the same as scanf. How would you use scanf to solve your problem?

**Pztar** · 05-25-2011

Well I sort of got it figured out.. But fgets is reading the whitespace and then just stopping. How can I make it skip to the next line?

**tabstop** · 05-25-2011

fgets most assuredly does not skip white space. It only stops at the end of the line.

**nonoob** · 05-25-2011

Something like this:

Code:

fgets(buffer, BUF_SIZE, filep);
sscanf(buffer, "%s %d %d", city, &dist1, &dist2);

**~~CommonTater~~** · 05-25-2011

Originally Posted by Pztar

I still don't know how to do it. I retrieve the information with fgets() that works fine for me.

But I can't get the information that I want with sscanf(). I'm not sure how to do it..

I've searched google, and I can't find what I'm looking for. I found something where the example used a sentence and that seems simple. But I don't know how to apply it to my situation.

I know I may be asking too much, but I just want to learn how to do it.

Cygnus C Support Library, Full - scanf

**Pztar** · 05-25-2011

Originally Posted by nonoob

Something like this:

Code:

fgets(buffer, BUF_SIZE, filep);
sscanf(buffer, "%s %d %d", city, &dist1, &dist2);

That's what I'm trying to do but it won't work. When I don't loop it, it returns 0 all the time. When I do, it returns only the values of the last line

**anduril462** · 05-25-2011

Perhaps you could post the simplest version of your code that demonstrates the problem?

**quzah** · 05-25-2011

Originally Posted by Pztar

That's what I'm trying to do but it won't work. When I don't loop it, it returns 0 all the time. When I do, it returns only the values of the last line

It sounds like when you are looping you are just writing to the same spot:

Code:

while( ... )
    sscanf( "%d", &putithere );
printf( "oh noes, putithere only contains the last entry: %d\n", putithere );

Quzah.

**Pztar** · 05-25-2011

Originally Posted by anduril462

Perhaps you could post the simplest version of your code that demonstrates the problem?

It's incorrect, I know. But I'm a beginner and I'm just trying to work it out.

Code:

while (fgets(rString, 100, fp))
		{
			
			sscanf(rString, "%s %d %d %d", iD, &R1, &R2, &RB);
			printf("%s %d %d %d", iD, R1, R2, RB);
			
		}

The main problem I'm getting now is, it's scanning the whitespace and returning odd values, and it's scanning the first set of strings. How can I get it to skip it? Thanks

**Pztar** · 05-25-2011

Originally Posted by anduril462

Perhaps you could post the simplest version of your code that demonstrates the problem?

It's incorrect, I know. But I'm a beginner and I'm just trying to work it out.

Code:

while (fgets(rString, 100, fp))
		{
			
			sscanf(rString, "%s %d %d %d", iD, &R1, &R2, &RB);
			printf("%s %d %d %d", iD, R1, R2, RB);
			
		}

The main problem I'm getting now is, it's scanning the whitespace and returning odd values, and it's scanning the first set of strings. How can I get it to skip it? Thanks

**quzah** · 05-25-2011

You are still going to be overwriting the same spot every time:

Code:

			sscanf(rString, "%s %d %d %d", iD, &R1, &R2, &RB);

Every pass through the loop will replace whatever value those variables have with new ones. If you need to keep track of multiples of each, then you probably want an array or something similar.

If you want to skip just a single line, call fgets once outside the loop first:

Code:

if( fgets( rString, 100, fp ) != NULL ) /* ignore first line */
{
    while( fgets( ... ) /* for each remaining line... */
    {
        ... do stuff
    }
}
else /* first line skip failed for some reason */
{
}

Quzah.

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