Ad:

C++ Discussion Thread
Unsolved
Views: 12735

May 25th, 2006

read data from file

Expand Post »

i write a program which write a value of a pointer into file using "out" now i need to read this data from the file but when i read it and print it on the screen a minus value appear.

can you help me by tell9ing me how to read data using "in" and why yhis problem occur

Similar Threads

how to read data from text file into data grid??? in VB.NET
Get data out of excel file stored as an image in MS SQL
help me to read my data file:(( in C
conversion of text file into data base file in Visual Basic 4 / 5 / 6
How to read data from csv file in an array and parse in C++

mhm_ra

Reputation Points: 10

Solved Threads: 0

Newbie Poster

Offline

16 posts
since Mar 2006

Permalink

May 25th, 2006

Re: read data from file

I guess you expect everyone to be mind readers. You will have to post your code

Ancient Dragon

Sponsor

Team Colleague

Featured Poster

Reputation Points: 5608

Solved Threads: 2283

Retired and Enjoying Life

Offline

21,963 posts
since Aug 2005

Permalink

May 25th, 2006

Re: read data from file

C++ Syntax (Toggle Plain Text)
#include<iostream>
#include <fstream>
#include <string>
using namespace std;
 
int main()
{
ifstream in("myfile.txt");
 
in>>address;
static_cast<long>(address);
 
cout<<address;
 
}
#include<iostream>
#include <fstream>
#include <string>
using namespace std;
 
int main()
{
ifstream in("myfile.txt");
 
in>>address;
static_cast<long>(address);
 
cout<<address;
 
}

Last edited by cscgal; May 25th, 2006 at 10:29 am.

mhm_ra

Reputation Points: 10

Solved Threads: 0

Newbie Poster

Offline

16 posts
since Mar 2006

Permalink

May 25th, 2006

Re: read data from file

what is variable "address"? where did you declare it?
also post the code that wrote the file. and the first line or two of the file contents.

>>static_cast<long>(address);
that line does nothing at all. you might as well delete it.

Ancient Dragon

Sponsor

Team Colleague

Featured Poster

Reputation Points: 5608

Solved Threads: 2283

Retired and Enjoying Life

Offline

21,963 posts
since Aug 2005

Permalink

May 25th, 2006

Re: read data from file

thank you for your interest
i try to defined address as a string and read data but didn't work
below is the code that write into a file

C++ Syntax (Toggle Plain Text)
 
#include <fstream>
#include <string>
using namespace std;
 
void main()
 
{  int arraysize=50;
   float **a;
	a=new float * [arraysize];
	for(int i=0;i<arraysize;i++)
	*(a+i)=new float[arraysize];
 
 
	float **b;
	b=new float * [arraysize];
	for( i=0;i<arraysize;i++)
	*(b+i)=new float[arraysize];
 
 
 	float **c;
	c=new float * [arraysize];
	for( i=0;i<arraysize;i++)
	*(c+i)=new float[arraysize];
 
 
	ofstream out("myfile.txt");
 
 
 
  for (i=0;i<arraysize;i++)
		for(int j=0;j<arraysize;j++)
		{
		a[i][j]=rand()*20 + 1 ;
 
		out<<(a + i*arraysize + j)<<endl;
 
		}  
 
 
for (i=0;i<arraysize;i++)
		for(int j=0;j<arraysize;j++)
		{
		b[i][j]=rand()*20 + 1 ;
 
		out<<(b + i*arraysize + j)<<endl;
 
		}  
 
		for (i=0;i<arraysize;i++)
		for(int j=0;j<arraysize;j++)
		{
		c[i][j]=rand()*20 + 1 ;
 
		out<<(c+ i*arraysize + j)<<endl;
 
		}  
 
/////////////////////////////////////////////////////////////////
	for(i=0;i<arraysize;i++)
		{ 
			for (int q=0;q<arraysize;q++)
			{	
				for(int j=0;j<arraysize;j++)
				{	c[i][q]=a[i][j]*b[j][q]+c[i][q];
				out<<(a + i*arraysize +j)<<endl;
				out<<(b +j*arraysize +q)<<endl;
				out<<(c + i*arraysize +q)<<endl;
				out<<(c + i*arraysize +q)<<endl;
				}//end of for i
 
			}//end of for q
		}//end of for i
 
 
 
		/////////////////////////////////////////////////////////////////
 
   out.close();
}
#include <fstream>
#include <string>
using namespace std;

void main()

{  int arraysize=50;
   float **a;
	a=new float * [arraysize];
	for(int i=0;i<arraysize;i++)
	*(a+i)=new float[arraysize];


	float **b;
	b=new float * [arraysize];
	for( i=0;i<arraysize;i++)
	*(b+i)=new float[arraysize];
	
	
 	float **c;
	c=new float * [arraysize];
	for( i=0;i<arraysize;i++)
	*(c+i)=new float[arraysize];

	
	ofstream out("myfile.txt");
   
	
   
  for (i=0;i<arraysize;i++)
		for(int j=0;j<arraysize;j++)
		{
		a[i][j]=rand()*20 + 1 ;
		
		out<<(a + i*arraysize + j)<<endl;
		
		}  


for (i=0;i<arraysize;i++)
		for(int j=0;j<arraysize;j++)
		{
		b[i][j]=rand()*20 + 1 ;
		
		out<<(b + i*arraysize + j)<<endl;
		
		}  

		for (i=0;i<arraysize;i++)
		for(int j=0;j<arraysize;j++)
		{
		c[i][j]=rand()*20 + 1 ;
		
		out<<(c+ i*arraysize + j)<<endl;
		
		}  

/////////////////////////////////////////////////////////////////
	for(i=0;i<arraysize;i++)
		{ 
			for (int q=0;q<arraysize;q++)
			{	
				for(int j=0;j<arraysize;j++)
				{	c[i][q]=a[i][j]*b[j][q]+c[i][q];
				out<<(a + i*arraysize +j)<<endl;
				out<<(b +j*arraysize +q)<<endl;
				out<<(c + i*arraysize +q)<<endl;
				out<<(c + i*arraysize +q)<<endl;
				}//end of for i
			
			}//end of for q
		}//end of for i



		/////////////////////////////////////////////////////////////////

   out.close();
}

mhm_ra

Reputation Points: 10

Solved Threads: 0

Newbie Poster

Offline

16 posts
since Mar 2006

Permalink

May 25th, 2006

Re: read data from file

and this is a first few lines from the file it represent a hexadecimal value

00481D70
00481D74
00481D78
00481D7C
00481D80
00481D84

mhm_ra

Reputation Points: 10

Solved Threads: 0

Newbie Poster

Offline

16 posts
since Mar 2006

Permalink

May 25th, 2006

Re: read data from file

Why are you using this form: (a + i*arraysize +j) rather than subscript notation a[i][j]?

It's simpler, for one, and it is also easier to see that (a + i*arraysize +j) means the same as &a[i][j].
Or that *(a + i*arraysize +j) means the same as a[i][j].

So what you are putting into your file are not the values you have created, but their location -- which is fairly meaningless.

It might be helpful to output some text into the file to denote matrices, and perhaps make them look like 2D matrices rather than one long column.

Also, MSVC6 uses incorrect scoping rules with variables declared in a for loop. I'd say just move your i, j, q outside of the loops.

And do you instead want % here?

(Toggle Plain Text)

a[i][j]=rand() * 20 + 1 ;

And main returns an int.

You may want to seed your random number generator. Often srand(time(0)); is used.

Dave Sinkula

Team Colleague

Reputation Points: 2780

Solved Threads: 312

long time no c

Offline

4,790 posts
since Apr 2004

Permalink

Jul 17th, 2010

-1

Re: read data from file

Good but provide CPP from basic

neela_482

Reputation Points: 4

Solved Threads: 0

Newbie Poster

Offline

1 posts
since Jul 2010

Permalink

Jul 18th, 2010

Re: read data from file

Click to Expand / Collapse Quote originally posted by neela_482 ...

Good but provide CPP from basic

Pointless reopening of 4 years old thread and on top of that absolutely rubbish advice.

Thread closed

peter_budo

Moderator

Featured Poster

Reputation Points: 2786

Solved Threads: 874

Code tags enforcer

Offline

6,659 posts
since Dec 2004

This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.

This thread is currently closed and is not accepting any new replies.

Previous Thread in C++ Forum Timeline: C++ Console document and server question.

Next Thread in C++ Forum Timeline: what is wrong with my code plss help?

DaniWeb Message

Cancel Changes

User Name
Password