overload operator <<

[wolfv]

In the first example, fstream works with operator << as expected.
The second example is similar, but with the fstream in a wrapper.
How to make it work with the operator <<?
My failed attempt to overload << is in the second example.

example 1:

#include <stdlib.h>
#include <iostream>
#include <fstream>

int main()
{
	char const* fileName="file1.txt";
	std::fstream of;

	of.open(fileName);

	if (of.is_open())
	{
		std::cerr << fileName << " opened for writing.\n";
	}
	else
	{
		std::cerr << fileName << " could not be opened for writing!\n";
		exit(0);
	}

	of << "hello";		//'hello' appears in file1.txt
}

example 2:

#include <stdlib.h>
#include <iostream>
#include <fstream>
#include <istream>

class OutFile
{
	private:
		std::fstream outf;
	public:
		void initialize(char const* fileName);
};

void OutFile::initialize(char const* fileName)
{
	outf.open(fileName);

	if (outf.is_open())
	{
		std::cerr << fileName << " opened for writing.\n";
		return;
	}
	std::cerr << fileName << " could not be opened for writing!\n";
	exit(0);
}

//overload <<
OutFile& operator<<(OutFile& outf, std::istream& in)
{
	outf << in;
	return outf;
}

int main()
{
	char const* fileName="file2.txt";
	OutFile of;

	of.initialize(fileName);
	of << "hello";		//compiles and runs when this line is commented
}

example 2 output:

C:\Users\wolf\Documents\demo_MinGW\OutFile>g++ main.c
main.c: In function 'int main()':
main.c:40:5: error: no match for 'operator<<' (operand types are 'OutFile' and '
const char [6]')
  of << "hello";  //compiles and runs when this line is commented
     ^
main.c:40:5: note: candidate is:
main.c:28:10: note: OutFile& operator<<(OutFile&, std::istream&)
 OutFile& operator<<(OutFile& outf, std::istream& in)
          ^
main.c:28:10: note:   no known conversion for argument 2 from 'const char [6]' t
o 'std::istream& {aka std::basic_istream<char>&}'

Maybe example 2 is not the best way to write the OutFile class.
Would it be better to use a wrapper or inherit from fstream?

Thand you.

[coder777]

Overloding the stream operators requires the stream as the first parameter and the result:

std::istream& operator>>(std::istream& in, OutFile& outf)
{
	in >> outf;
	return in;
}

But what I think you rather want is this:

#include <stdlib.h>
#include <iostream>
#include <fstream>
#include <istream>

class OutFile
{
	private:
		std::fstream outf;
	public:
		void initialize(char const* fileName);

OutFile& operator<<(char const* data) // Note
{
  outf << data;
  return *this;
}
};

void OutFile::initialize(char const* fileName)
{
	outf.open(fileName);

	if (outf.is_open())
	{
		std::cerr << fileName << " opened for writing.\n";
		return;
	}
	std::cerr << fileName << " could not be opened for writing!\n";
	exit(0);
}

int main()
{
	char const* fileName="file2.txt";
	OutFile of;

	of.initialize(fileName);
	of << "hello" << "world";	
}

[wolfv]

Thank you coder777! That worked beautifully.