hey everyone, i am in desperate need with something soooo simple!!!

Question

theonlywalks 0 Newbie Poster

14 Years Ago

Hey everyone, I have a simple simple problem that is literally driving me insane.

Basically, I have a database of numbers seperated my spaces. I just took a segment of my code because I am soooo completely lost with the output!!

If the database is:

1 2 3 9 7 6 4 5 6 7

I don't understand why my output is 1 for every single line??? How is the sscanf statement not taking the next string??

Someone please help I am desperate!!

#include <stdio.h>

main()
{
	
	char buffer[20000];
	char pid_temp[501], arrival_time_temp[501], CPU_burst_temp[501], IO_burst_temp[501];	
	FILE *fp;
	
	fp = fopen("CPULoad.dat", "r");
	fgets(buffer, 20000, fp);	
	
	fp = fopen("CPULoad.dat", "r");
	fgets(buffer, 20000, fp);
	
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	
	close(fp);
}

c++

Edited 14 Years Ago by theonlywalks because: mistake in title

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Latest Post 14 Years Ago Latest Post by Dave Sinkula

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WaltP 2,905 Posting Sage w/ dash of thyme

14 Years Ago

Hey everyone, I have a simple simple problem that is literally driving me insane.
Basically, I have a database of numbers seperated my spaces. I just took a segment of my code because I am soooo completely lost with the output!!
If the database is:
1 2 3 9 7 6 4 5 6 7
I don't understand why my output is 1 for every single line??? How is the sscanf statement not taking the next string??
Someone please help I am desperate!!

You have a data base or a data file?

It's obvious that your code doesn't run.

fp = fopen("CPULoad.dat", "r");
	fgets(buffer, 20000, fp);	
	
	fp = fopen("CPULoad.dat", "r");
	fgets(buffer, 20000, fp);

You cannot open the same file twice, so you never get to any output at all.

Please either describe the real problem or post the real code.

WaltP 2,905 Posting Sage w/ dash of thyme

14 Years Ago

Here's what I see.

sscanf(buffer, "%s", CPU_burst_temp);  // what is the value of buffer here?
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);  // what is the value of buffer here?
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);  // what is the value of buffer here?
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);  // etc...
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);

What is changing buffer?

Edited 14 Years Ago by WaltP because: n/a

WaltP 2,905 Posting Sage w/ dash of thyme

14 Years Ago

It ignores preceding whitespace. But If you don't remove the '1', buffer never changes so you keep reading it.

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theonlywalks 0 Newbie Poster · Answer 1 · 2010-03-08T04:02:05+00:00

Hi, I'm sorry, I was copy and pasting my code and I pasted part of it twice for some reason.

Basically, I have a text file that is like this:

1 2 4 8 11 66 77 11

So I use fgets to put the first line into a buffer, but when I try to read from the buffer, with sscanf, it only reads the first number, over and over again.

How do you read subsequent numbers, or strings? My output looks like:

1
1
1
1
1
1

instead of:
1
2
4
8
11
...

#include <stdio.h>

main()
{
	
	char buffer[20000];
	char pid_temp[501], arrival_time_temp[501], CPU_burst_temp[501], IO_burst_temp[501];	
	FILE *fp;
	
	fp = fopen("data", "r");
	fgets(buffer, 20000, fp);	
	
	
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	sscanf(buffer, "%s", CPU_burst_temp);
	printf("%s\n", CPU_burst_temp);
	
	close(fp);
}

theonlywalks 0 Newbie Poster · Answer 2 · 2010-03-08T04:14:40+00:00

hmm, well the buffer doesn't change, and the value of CPU_burst_temp remains 1 at all the statements.

But I thought that sscanf would read ignore the whitespace, and read the string until either the char array filled up, or it found an EOF or whitespace. And then the next time you invoke sscanf again, it would continue scanning where it left off?

theonlywalks 0 Newbie Poster · Answer 3 · 2010-03-08T04:44:55+00:00

It ignores preceding whitespace. But If you don't remove the '1', buffer never changes so you keep reading it.

ahh, i see, would you mind telling me how to remove the one, or advance the pointer position because I am not sure how to.

WaltP 2,905 Posting Sage w/ dash of thyme Team Colleague · Answer 4 · 2010-03-08T07:27:06+00:00

I think you can figure it out if you put your thinking cap on...

Dave Sinkula 2,398 long time no c Team Colleague · Answer 5 · 2010-03-08T07:49:07+00:00

You're using sscanf as if it were fscanf. You can make the two behave similarly, but sscanf will need different directives and variables.

thomas_naveen 105 Junior Poster · Answer 6 · 2010-03-08T10:54:09+00:00

You could consider strtok instead of sscanf.

I hope the large sized arrays are justified. You could end up corrupting your stack.

EricDLundquist 0 Newbie Poster · Answer 7 · 2010-03-08T22:17:49+00:00

you could write NULL to the buffer after each write/print

i.e

buffer = '\0'

Dave Sinkula 2,398 long time no c Team Colleague · Answer 8 · 2010-03-09T00:44:38+00:00

You could consider strtok instead of sscanf.

Parsing a String into Tokens Using sscanf

Many times strtok is recommended for parsing a string; I don't care for strtok . Why?
It modifies the incoming string, so it cannot be used with string literals or other constant strings.

The identity of the delimiting character is lost.

It uses a static buffer while parsing, so it's not reentrant.

It does not correctly handle "empty" fields -- that is, where two delimiters are back-to-back and meant to denote the lack of information in that field.

This snippet shows a way to use sscanf to parse a string into fields delimited by a character ...

The empty fields may be about the only thing that comes closest.

But anyways, the above linked snippet shows how to use sscanf to parse multiple elements from the same line. The earlier posted attempt seemed to be using sscanf as if it were fscanf (which could also be used if you so choose) -- as illustrated by WaltP (scanning the same text over and over and expecting different results).

hey everyone, i am in desperate need with something soooo simple!!!

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