C++ issues reading from files - Overclock.net

NameUnknown · 4 Weeks Ago

Ive never been good at reading from files in C++, but at the same time Ive never had this much trouble with it either. And Im almost guaranteed to be overlooking a stupid and simple issue with the code, but whatever it is, I cant find it.

On to the issues with this program though. for this program i have to read in values from a .txt file and then add 10 to each value and output it all into a new file. Ive got it outputting fine, but it wont read write. All I get depending on how I write it is 0, 10, or -858993450, never the right answer.

As you can see, it initially checks to make sure it isnt at the end of the file, and if it is it exits, if not, it goes on to do the calculations. Well as said above the calculations dont give any real results, and then it just sits in an infinite loop instead of jumping out at the end of the file.

Unless Im missing something (which I probably am) then there isnt anything wrong, but who knows, I missed lecture last week because i wasn feeling well.

Code:

#include <iostream>
#include <fstream>

using namespace std;

int main ()
{
	int NumIn;
	int NumOut;

	ifstream infile("C:\in.txt", ios::in);
	ofstream outfile("C:\out.txt", ios::out);

	if (infile.eof())
	{
		cout << "There are no more data points int eh data source." << endl;
		cout << "The program will now exit" << endl;
	}	
	
	else (!infile.eof())	
	{
		while (!infile.fail())
		{
			infile >> NumIn;
			outfile << (NumIn + 10) << endl;
			cout << (NumIn + 10) << endl;
		}	
	}	

	infile.close();
	outfile.close();
	
	system("PAUSE");
}

Twinnuke · 4 Weeks Ago

Is it possible you aren't supposed to have the "" around the file name?

scratch that i just wasnt paying attention, i know where it comes from now.

NameUnknown · 4 Weeks Ago

Ive got quotes around both file paths :\

Korben · 4 Weeks Ago

Try something like this.

Code:

#include <fstream>
#include <iostream>
#include <iomanip>
using std::cout;
using std::endl;


int main() 
{
	const char* filename = "test.txt";
	std::ifstream inFile(filename);

	// Make sure the file stream is good
	if(!inFile) 
	{
		cout << endl << "Failed to open file " << filename;
		return 1;
	}

	int n = 0;
	while(!inFile.eof()) 
	{
		inFile >> n;
		int x = n+10;
		cout << x << endl;
	}
	cout << endl;
	system("pause");
	return 0;
}

edit:

I probably should have just told you what was wrong with yours instead. I had to do this to get it working for your file.

Code:

#include <iostream>
#include <fstream>

using namespace std;

int main ()
{
	int NumIn;
	int NumOut;

	ifstream infile("c://in.txt", ios::in);//use string literal // to create backslash / 
	ofstream outfile("c://out.txt", ios::out);//^^ vice versa

	if (infile.eof())
	{
		cout << "There are no more data points int eh data source." << endl;
		cout << "The program will now exit" << endl;
	}	
	
	else if (!infile.eof())//cannot have parameters for else needs to be else if
	{
		while (!infile.fail())
		{
			infile >> NumIn;
			outfile << (NumIn + 10) << endl;
			cout << (NumIn + 10) << endl;
		}	
	}	

	infile.close();
	outfile.close();
	
	system("PAUSE");
}

Pooping^fish · 4 Weeks Ago

You check for EOF before even reading, what the ****?

Also, you need to handle data types. this isnt your little scripting language, its up to you to do things correctly. Cast and/or atoi() values.
Id also suggest manually parsing the file as always, its your best bet. Have a common data format for the program and error check for anything else.

Also, dont use the System() call if you plan on distributing this at all.

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C++ issues reading from files

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