Works in UNIX but not windows? - Overclock.net

The Hundred Gunner · 10-08-08

Can someone tell me why this program works in UNIX (OSX, more specifically) but not in windows? The goal of the program is to read a series of numbers from a file and report the largest and smallest ones. Here's the program in a nutshell:

1. Ask what file to use to input data
2. Check if the file exists
3. If so, check that the file actually contains numbers
4. If so, check what is the greatest number by comparing values
5. Check what is the smallest number by comparing the values

In UNIX, the program works flawlessly. When I copy the code to windows and build, the program works correctly EXCEPT for the reporting of the least number, I get garbage. I have no idea why this works in one OS, but in the other it works half-assed. Here's the code:

Code:

#include <iostream>
#include <string>
#include <fstream>
using namespace std;

int main(void)
{
	long largest, smallest, temp;
	
	string file;	//For which file to use to import data
	
	int file_contains_values;
	
	cout << "Get data from which file? ";
	cin >> file;
	
	ifstream data_list;
	
	data_list.open(file.c_str());
	
	if (!data_list)	//If no file, exit program
	{
		cout << "The file \"" << file << "\" could not be read." << endl;
		cout << "The program will now exit.  Press any key to continue.\n";
		getchar();
		getchar();
		return 0;
	}
	
	else
	{
	
	if (data_list >> file_contains_values == 0)	//If read of values fails, program closes.
		{
			cout << "There is no data in " << file << ".  The program will now exit.\n";
			getchar();
			getchar();
			return 0;
		}
		
		else
		{
		data_list.close();	//Close the file and open again to start from beginning
		data_list.open(file.c_str());	/*b/c 1st value was used to determine if numbers existed,
											the file will be read from 2nd value otherwise*/
	
		cout << endl << "Checking for largest number...\n";
		data_list >> largest;
		
		do
		{
			data_list >> temp;
			
			if (temp > largest)
			largest = temp;		
		
		} while (!data_list.eof());
		data_list.close();	//Close the file
		
		cout << "The largest number in the list is " << largest << endl << endl;
		
		cout << "Checking for the smallest number...\n";
		data_list.open(file.c_str());
		data_list >> smallest;
		
		do
		{
			data_list >> temp;
			
			if (temp < smallest)
			smallest = temp;
		} while (!data_list.eof());
		
		cout << "The smallest number is " << smallest << endl << endl;
		data_list.close();
		}
		
	}
	
	return 0;
}

Any help is apreciated.

Manyak · 10-08-08

You shouldn't keep closing and reopening the file over and over. Instead of doing that, why don't you try using:

Code:

seekg(ios_base::beg);

That will send the read pointer back to the beginning of the file. This will most likely fix the problem.

The Bartender Paradox · 10-08-08

It could be that your assumption that your .close() - .open() sequence resetting the file pointer back to 0 is not correct on the system you are compiling on, or it could not be resetting the EOF flag. Try checking for EOF just before and just after the first time you read in smallest.

Or I could just be off my rocker

What compiler are you using?

The Hundred Gunner · 10-08-08

Quote:

Originally Posted by Manyak

You shouldn't keep closing and reopening the file over and over. Instead of doing that, why don't you try using:

Code:

seekg(ios_base::beg);

That will send the read pointer back to the beginning of the file. This will most likely fix the problem.

That actually made UNIX reproduce the error that I would otherwise ONLY experience in windows

I actually tried a few things based on this reference:

http://www.cplusplus.com/reference/i...eam/seekg.html

I tried:

Code:

data_list.seekg(ios_base::beg);

and

[code]data_list.seekg(0, ios::beg);[/quote]

Both produce a garbage number for smallest, even though largest is given the correct value. The garbage value seems to be different for the two above.

Quote:

Originally Posted by The Bartender Paradox

It could be that your assumption that your .close() - .open() sequence resetting the file pointer back to 0 is not correct on the system you are compiling on, or it could not be resetting the EOF flag. Try checking for EOF just before and just after the first time you read in smallest.

Or I could just be off my rocker

What compiler are you using?

If the EOF flag isn't being reset, how would I reset it?

The compiler I'm using in OSX is g++, and the compiler I'm using in windows is Visual C++ Express.

Manyak · 10-08-08

Hrm...can you put a couple of cout statements at the beginning and middle of both the largest and smallest loops? This way we can see exactly when the garbage comes up.

Like this:

Code:

		cout << "Checking for the smallest number...n";
		data_list.open(file.c_str());
		data_list >> smallest;
		cout << "Initial: " << smallest << endl;
		do
		{
			data_list >> temp;
			cout << "Next Smallest: " << temp << endl;
			if (temp < smallest)
			smallest = temp;
		} while (!data_list.eof());
		
		cout << "The smallest number is " << smallest << endl << endl;
		data_list.close();

Its possible that the program is only reading garbage after a certain number of reads, and that garbage happens to be a really low negative number (bitwise), which is why it doesn't cause an error in the "largest" loop.

I'm actually betting now that the garbage read is only the last one.

error10 · 10-08-08

Why are you reading the file twice at all? Just read it once.

The Hundred Gunner · 10-10-08

Quote:

Originally Posted by error10

Why are you reading the file twice at all? Just read it once.

If I don't do the opening/closing, then the next time I want to read from the list, it doesn't start from the top. I need it to start from the top, and the only way I know how to do that is to close then open the file again.

error10 · 10-10-08

Yeah, but the point is, you only NEED to read the file once!

Manyak · 10-10-08

Quote:

Originally Posted by The Hundred Gunner

If I don't do the opening/closing, then the next time I want to read from the list, it doesn't start from the top. I need it to start from the top, and the only way I know how to do that is to close then open the file again.

He means that as you read it the first time, check both variables at once.

Code:

		data_list.open(file.c_str());
		if (!(data_list >> temp))
		{
			cout << "There is no data in " << file << ".  The program will now exit.n";
			return 0;
		}
		
		// If the program didn't exit, then temp will already contain the first entry
		// So put the initial value into both smallest and largest
		// And check both in one loop
		smallest = temp;
		largest = temp;
		
		do {
			data_list >> temp;

			if (temp < smallest)
				smallest = temp;

			if (temp > largest)
				largest = temp;
		} while (!data_list.eof());
		
		cout << "The smallest number is " << smallest << endl;
		cout << "The largest number is " << largest << endl;
		data_list.close();

This way you only have to read the file once.

The Hundred Gunner · 10-10-08

Yeah, a friend ended up telling me that I could have just done it all at once... But I'm still stumped as to what's making it F up in windows but it works just fine in UNIX. My class TA is stumped as well.

Anyway, thanks to you all.

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Works in UNIX but not windows?

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