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Reading specific numbers in a .txt file and record them in an array

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amegahed3

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Reading specific numbers in a .txt file and record them in an array

Apr 17th, 2009

Hi All,

I'm a C++ beginner, and I face the following problem:

There's a .txt file that has some number written successively in the 15th line of the file. Each number (that could be a one or 2 digits number) is separated by a space from the preceding and succeeding numbers.

What I want to do is to read each of those numbers (their total number is 333) and store each of them( in its specific order) in an array of integers. i.e. I need to have an array declared as int [333], and each of its entries is one of the 333 numbers in the same order they appear in the text file.

Suppose that the file is called input.txt and that its path is c:\input.txt.

Could you please provide me with a simple code for that?

Thanks a lot.

Aly

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nucleon

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Re: Reading specific numbers in a .txt file and record them in an array

Apr 17th, 2009

What does "written successively in the 15th line" mean?
Do you mean starting at the 15th column?

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Re: Reading specific numbers in a .txt file and record them in an array

Apr 17th, 2009

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Originally Posted by nucleon

What does "written successively in the 15th line" mean?
Do you mean starting at the 15th column?

It means that line 15 (row 15) in the .txt file has the following structure for example:

2 23 434 22 12 4 7 9 0 1 4 8 9

And all what I need to do is to read those numbers (that are again in the 15th line of the .txt file, and store them in an integer array. So, for example, for the previous example, the array that I want should be like this:

A[1]=2
A[2]=23
A[3]=434
A[4]=22

And so on.

Hope it's clear now. Thanks for your help in advance.

Aly

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Re: Reading specific numbers in a .txt file and record them in an array

Apr 18th, 2009

Declare your integer array and an ifstream:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
int A[333];
ifstream input;
int A[333];
ifstream input;

Skip the first 14 lines using getline to grab the line up to the newline and then do nothing with it. You've now reached the 15th line.

Set up a loop and read in the 333 integers:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
for (int i = 0; i < 333; i++)
    input >> A[i];
for (int i = 0; i < 333; i++)
    input >> A[i];

Close the ifstream.

Note that array indexes should start with 0, not 1.

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Re: Reading specific numbers in a .txt file and record them in an array

Apr 18th, 2009

Thanks a lot for your reply.

Actually, I tried the ideas you told me about. I think my problem is with getline. Here's my code, which compiles, but doesn't give any results (it takes forever at getline):

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <fstream>
#include <iostream>
#include <stdio.h>
#include <string>
#include <cstdlib>
using namespace std;
 
int main (void)
{
	int A[333];
	char name[1000];
	ifstream filein;
	filein.open("input.txt");
	for(int h=0;h<9;h++){
		cin.getline(name,10);
	}
 
	for (int i = 0; i < 6; i++)
		filein>> A[i];
 
	filein.close();
	for(int yy=0;yy<7;yy++){
		cout<<A[yy];
	}
 
	return 0;
}
#include <fstream>
#include <iostream>
#include <stdio.h>
#include <string>
#include <cstdlib>
using namespace std;

int main (void)
{
	int A[333];
	char name[1000];
	ifstream filein;
	filein.open("input.txt");
	for(int h=0;h<9;h++){
		cin.getline(name,10);
	}

	for (int i = 0; i < 6; i++)
		filein>> A[i];

	filein.close();
	for(int yy=0;yy<7;yy++){
		cout<<A[yy];
	}

	return 0;
}

Could you please help me with my mistake?

Thanks.

Aly

Last edited by amegahed3; Apr 18th, 2009 at 4:01 am.

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Re: Reading specific numbers in a .txt file and record them in an array

Apr 18th, 2009

You opened filein and you're reading from cin.

The 3 Laws of the Procrastination Society:
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2) Tomorrow never comes

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Re: Reading specific numbers in a .txt file and record them in an array

Apr 18th, 2009

Ooooh, what a stupid mistake.
Thanks a lot, man. It now works fine.

I just have one last question:

If that 15th line contains "value=" and then the numbers (with a space between each 2 numbers). How can I skip those initial characters, and begin reading and storing my numbers in A[]?

So, to make it more clear, in my .txt file, the 15th line looks like this for example:

value= 1 22 434 3 100

And I want to have an array of integers A[7], where:
A[1]=1
A[2]=22
A[3]=434
A[4]=3
A[5]=100

How can that be done, please?

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Re: Reading specific numbers in a .txt file and record them in an array

Apr 18th, 2009

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Originally Posted by amegahed3

Ooooh, what a stupid mistake.
Thanks a lot, man. It now works fine.

I just have one last question:

If that 15th line contains "value=" and then the numbers (with a space between each 2 numbers). How can I skip those initial characters, and begin reading and storing my numbers in A[]?

So, to make it more clear, in my .txt file, the 15th line looks like this for example:

value= 1 22 434 3 100

And I want to have an array of integers A[7], where:
A[1]=1
A[2]=22
A[3]=434
A[4]=3
A[5]=100

How can that be done, please?

If you know FOR SURE that there is NO space between "value" and "=" and that there IS a space between "=" and the first number, just read "value=" into a string and throw it away before you read in the numbers:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
string throwAway;
filein >> throwAway; // read in "value="
for (int i = 0; i < 333; i++)
    filein >> A[i]; // read in numbers
string throwAway;
filein >> throwAway; // read in "value="
for (int i = 0; i < 333; i++)
    filein >> A[i]; // read in numbers

Again, this only works if the assumptions listed above are valid.

Last edited by VernonDozier; Apr 18th, 2009 at 12:40 pm. Reason: screwed up on sample code

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Re: Reading specific numbers in a .txt file and record them in an array

Apr 18th, 2009

Thanks a lot. That totally solves all my problems.

I really appreciate it. You guys are so helpful!

Aly

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amegahed3

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Re: Reading specific numbers in a .txt file and record them in an array

#10

Apr 18th, 2009

I'm really sorry guys for the continuous disturbance, but on another thought, I found that my .txt file, its 15th line is in the form of:

value =1 22 434 3 100

Which means that there is a space between the word "value", and "=", while there is no space between "=" and the first number that I want to read.

Now, if I read 2 throwaway strings, the first number is read with the "=" in the second string, and so, the first number is not read in A[0]. How can that be solved in this case?

Thanks in advance.