How to input values from *.txt to an array in C++

HBMSGUY · 11-16-2008, 10:39 PM

Hello I am looking for a way to take data from a *.txt file, as part of my bigger project. The file looks like this:
1 0.0 0.0
2 10.1 -10.1
3 -12.2 12.2
4 38.3 38.3
5 79.99 179.99

Now I don't mean to be picky, but I want it to go into an array of doubles like this.
originalData[0][0] = 1
originalData[0][1] = 0.0
originalData[0][2] = 0.0
originalData[1][0] = 2
originalData[1][1] = 10.1
and it continues.

There is one last thing: The file will always be in this format with each line being complete, although I don't know till the time of execution how many lines there will be.

Thanks so much, it really helps.

Nylex · 11-17-2008, 01:08 AM

Please make sure you choose your forum more carefully in future!

Two things I can think of for doing this:

1. Go through the file, checking how many lines there are and then create your array based on that.

2. Just put all the numbers into a C++ vector (they're like arrays, but can grow and shrink) and since you know each line in the file contains 3 values, dividing the size of the vector by 3 will give you the number of lines..

There may be other, better ways of approaching your problem, but these are just the ways I could come up with.

HBMSGUY · 11-17-2008, 07:01 PM

Thank you very much for the reply, that is what looks like to me a good way to store the data. I am sorry I got this in the wrong category, I could have sworn I picked programming. But, I still I am not understanding how to take the information from the file. I have looked at the <ifstream> but the when I use get, it get() it gives me two characters. And read will not read just a character.
Thanks for the help.

Nylex · 11-17-2008, 11:37 PM

Do you know how to read input from the console using cin? If so, you can read from a file in the same way, but using an ifstream object, e.g.

Code:

ifstream in("file.txt");
double d;

// Loop will break when there are no more values to read
while(in >> d)
{
  // Do stuff
}

Edit: This will read individual values. If you want entire lines, then use getline() (but then you'd have the issue of splitting that line up into its constituent elements).

HBMSGUY · 11-17-2008, 11:51 PM

Thanks, I am starting to see that I was over thinking the input task. I am guessing that the way the >> operator works is it will just read the next value. Then next time the loop repeats it will read the numeric value after, and so on. Thanks so much, I really appreciate the help.

Nylex · 11-18-2008, 12:22 AM

Quote:

Originally Posted by HBMSGUY

Thanks, I am starting to see that I was over thinking the input task. I am guessing that the way the >> operator works is it will just read the next value. Then next time the loop repeats it will read the numeric value after, and so on. Thanks so much, I really appreciate the help.

Yes and yes and no problem

.

reddazz · 11-18-2008, 09:33 PM

Moved: This thread is more suitable in the Programming forum and has been moved accordingly to help your thread/question get the exposure it deserves.