File input from method?

[Tiny_trixer]

I was wondering. Is there a way to write something from one method in to a result file instead of outputting to screen?

To describe a little better, in pseudocode:

#include <iostream>
#include <fstream>

using namespace std;

class Inputoutput
{
private:
	ifstream fileOne;
	ofstream fileTwo;
        int i;
        //More variables here off course. Int's and stuff...

public:
	// In the original program this method 
        // has an output to screen:
	void outputFromFileToScreen()
	{
		fileOne.open("file.txt", ios::in);

                for(i = 0; i < 16 && !fileOne.eof(); i ++)
			{
				fileOne.get(chars[i]);
			} // end for
		infile.close();

		for(j = 0; j <i; j ++)
			{
				cout << (int) c[j];
			} // end for
	} // end methode
}; // end class

Now instead of outputting this to screen by calling this method from main I would like to do something like:

int main()
{
	ofstream resultMethod;

	resultMethod.open("resultFile.dat", ios::out);
	resultMethod << io.del3(); // Pass the output to resultFile instead of screen?
} // end main

But trying this just gives a "no operator "<<" matches these operands". And I'm at a loss. Trying to find a tutorial that shows how to output stuff from methods to a file but I can't find anything...?

[drkybelk]

you have to write your own operator for class Inputoutput:

ostream& operator << (ostream& os, const Inputoutput& io)
{
   // here you have to implement how you want to output
   os << io.someMember << "," << io.anotherMember();
   return os;
}

you might need to declare the new (global!) << operator as a friend to your
class, if it accesses private or protected members.
Once you created the override for your class, you can also use it with cout and cerr:

Inputoutput io;
cout << io << endl; // will be fine

[Tiny_trixer]

Hmmm, okey. I'll give it a try! Thank you for pointing me in the right direction!

[Tiny_trixer]

OK, so I tried doing this:

friend ostream& operator<<(ostream& out, IOmetoder &io);

// Code code
// code code code

ostream& operator<<(ostream& out, const Inputoutput &io)
{
	out << io.method1() << io.resultMethod(); // ***
	return out;
} // end metode

***Trying to say that when << is used with this, then the stuff done in method1 should be written to resultMethod. But then I get the "no operator "<<" matches these operands" between out and io.method1().

The thought was to then have the resultMethod() go something like this:

void resultMethod()
	{
		result.open("thisfile.dat");

		cout << io << endl;

		result.close();
	} // end metode

And then call this method from main.

But I've only done a couple of programs with operator overloading in the past and those did not invovle files. Just simple stuff like:

ostream& operator<< (ostream &out, Point &onePoint)
{
    out << "(" << onePoint.xvalue << ", " << onePoint.yvalue << ")";
    return out;
}

(Used for simple coordinates)

So again I'm at a loss... Trying to consult the books and online tutorials of the world to find a solution.

[drkybelk]

Sorry I should have been clearer:

out << val1 << meth2() << val3 << val4 << meth5();

for all your val_x and meth_y() the operators have to be defined also.
Don't worry too much cos for all the built-in types and some STL types they are already defined (everything you can print out with cout <<. But the methods have to return something that you can print. void won't work.

[Tiny_trixer]

Ah! Okey. Now it's a little clearer. Thank you for helping!

[drkybelk]

Strictly speaking the operator(s) described above do not neccessarily write to files, but to streams. You can use them to write to strings, devices, and more without re-writing them. That's actually quite useful.