File Input Question

[a]

(I've reached that familiar place where I've got a nagging little
problem in a program I'm writing but I've been staring at code for too
long and I probably wouldn't be able to recognize the answer even if I
was staring right at it.)

I'm trying to design a function that reads input from my data file into
(a pair of) arrays. Simple enough? However, each line of the file is
either going to be 4 integers or a character (then a carriage return)
and I'm not sure which (i.e. there could be 4 integers followed by
another line of 4 integers followed by a letter or it could just be 1
letter/1 letter/1 letter). If the input is a character, it goes into
charArray, but if the input are those 4 integers, then they take up the
next 4 spots in intArray.

So, basically, I need to know how to read in something from a file when
I don't know its type. Also, I'm a bit rusty on the C++ and I've never
done file I/O so I'm trying to do this in the simplest way possible but
most of the file input examples I've seen online contain many function
calls that I don't understand. So when explaining, please do the typing
equivalent of speaking loudly and slowly =)





//The initializations are simple enough:
int in1, in2, in3, in4;
char ch1;

ifstream file_in;
file_in.open("test.txt");

if (!file_in)
{
cout << "Cannot open the file test.txt" << endl;
return (-1);
}

//And I think I have the while loop:
while( (file_in >> in1 >> in2 >> in3 >> in4 ) || (file_in >> ch1) )

//But then, I'm not sure how to check for type with my input


thanks in advance,
-frank (email: (e-mail address removed))

 

[Attila Feher]

(I've reached that familiar place where I've got a nagging little
problem in a program I'm writing but I've been staring at code for too
long and I probably wouldn't be able to recognize the answer even if I
was staring right at it.)

I'm trying to design a function that reads input from my data file
into (a pair of) arrays. Simple enough? However, each line of the
file is either going to be 4 integers or a character (then a carriage
return) and I'm not sure which (i.e. there could be 4 integers
followed by another line of 4 integers followed by a letter or it
could just be 1 letter/1 letter/1 letter). If the input is a
character, it goes into charArray, but if the input are those 4
integers, then they take up the next 4 spots in intArray.

[SNIP]

Since you input is line based, you will need to use the getline
functionality. Get the line into an std::string and when it is there, you
can find out if it is a 4*int or a 1*char. Be careful that a 1*char looks
just like a 1*int.

The iostream extract operator makes no difference between the any whitespace
and the end of line, so your approach with the two reads hoping that the int
reader will fail on a char is wrong. If the char happens to be 1, it will
read it as the first integer. If there are 4 lines like this you will get 4
intergers and so forth.

If you did read a line into a string you can easily check if it has one
character in it or not (by looking at the size). If not put this string
into an istringstream and get the 4 integers out.

 

[a]

Since you input is line based, you will need to use the getline

functionality. Get the line into an std::string and when it is there, you
can find out if it is a 4*int or a 1*char. Be careful that a 1*char looks
just like a 1*int.

The iostream extract operator makes no difference between the any whitespace
and the end of line, so your approach with the two reads hoping that the int
reader will fail on a char is wrong. If the char happens to be 1, it will
read it as the first integer. If there are 4 lines like this you will get 4
intergers and so forth.

If you did read a line into a string you can easily check if it has one
character in it or not (by looking at the size). If not put this string
into an istringstream and get the 4 integers out.

Oops, I have a small problem. I reread what I wrote and I said exactly
4 but it's actually anywhere from 1 to 4 integers on a line.
Unfortunately, as you mentioned in the first paragraph, this creates a
problem when I'm just trying to search on length alone. Is there any
way to test for data type of the input rather than length of it?

-frank

-frank

 

[Attila Feher]

Oops, I have a small problem. I reread what I wrote and I said
exactly 4 but it's actually anywhere from 1 to 4 integers on a line.
Unfortunately, as you mentioned in the first paragraph, this creates a
problem when I'm just trying to search on length alone. Is there any
way to test for data type of the input rather than length of it?

Frank. Honestly. Who made that specification? Please let me know:

1
1
1

Was this 3 lines of one characters or 3 lines of one integer?

 

[a]

Frank. Honestly. Who made that specification? Please let me know:

1
1
1

Was this 3 lines of one characters or 3 lines of one integer?

As for who made that design spec- it's poor data structure design. I'm
in the process of refining it. Obviously it still has some work to go.
*sheepish grin*

Basically, the concept is that if a player (each designated by a letter)
plays a variable number of games per week, hence the different number
of, well, numbers. Basically, in the example below, player A (I'll get
names implemented later- I'm just working on getting the smaller issues
right first- but that string is another reason why I want to be able to
determine things via data type) only had x number of games each week (2,
1, 3 in the example below) and the numbers denote the number of points
per game.

A
8 12
1
2 3 5


As for
1
1
1
Those would all count as integers. Single integers are not characters-
sorry for not clarifying.

-frank

 

[Attila Feher]

a wrote:
[NIP]

Basically, the concept is that if a player (each designated by a
letter) plays a variable number of games per week, hence the
different number of, well, numbers. Basically, in the example below,
player A (I'll get names implemented later- I'm just working on
getting the smaller issues right first- but that string is another
reason why I want to be able to determine things via data type) only
had x number of games each week (2, 1, 3 in the example below) and
the numbers denote the number of points per game.

A
8 12
1
2 3 5

OK. As I said: read lines into an std::string using getline, since your
file is lone based. Then check the first character if it is a letter.
Let's suppose you are only using that English 26, so it should be pretty
simple. If it is a letter, you have it: a new player. If it is not, it is
better be a number, because you put Mr. Std. String into a stringstream and
read integers from it one by one in a loop, until you can.

 

[Mike Wahler]

As for who made that design spec- it's poor data structure design. I'm
in the process of refining it. Obviously it still has some work to go.
*sheepish grin*

Basically, the concept is that if a player (each designated by a letter)
plays a variable number of games per week, hence the different number
of, well, numbers. Basically, in the example below, player A (I'll get
names implemented later- I'm just working on getting the smaller issues
right first- but that string is another reason why I want to be able to
determine things via data type) only had x number of games each week (2,
1, 3 in the example below) and the numbers denote the number of points
per game.

A
8 12
1
2 3 5

Why not change the file format to tell you this information?
E.g.

A 3 // 3 is number of following lines related to 'A'
2 8 12 // 2 is num of scores, 8 and 12 are the two scores
1 1 // 1 is num of scores, 1 is the single score
3 2 3 5 // 3 is num of scores, 2, 3, and 5 are the three scores.

As for
1
1
1
Those would all count as integers. Single integers are not characters-

Actually *everything* in a text file is a character,
including single digit characters such as '1'.
A sequence of digit characters can be converted
to an integer type, but that doesn't stop them
from being characters, i.e. valid as a string.

sorry for not clarifying.

If you say that a single numerical character does not
qualify as a 'character' in your file specification,
then you'll have to disallow such from being a 'player
name'.

I think it's much more effective to create a good design
for your file format, rather than trying to come up with
'fancy tricks' to try to decipher one with a limited amount
of information.

-Mike