redefine cout to directing one file, is impossible?

I want to save my test prog processing result showing to other
newbie, (haha, I am just a new new newbie)
I think is it possible to change cout direction from monitor to a file?
just like we often do in dos:

Code:

c:\>dir >>test.txt

The statement can save output directory list.

How to do in c++?

well in dos and linux its >(file) not >>(file)

If you want to do it inside the program instead of external you'll have to do something like:

Code:

std::ofstream outfile ("test.txt");
std::ostream out = outfile;

out<<"Hello world";

Then when you want to go back to the console you just change it to

Code:

std::ostream out = std::cout;

Or you could just use the operating system's redirection and save yourself a lot of trouble

@ Thantos :
Thanks, it's great.

I just test it,

Code:

#include <iostream>
#include <stdio.h>

using namespace std;

std::ofstream outfile ("c:test.txt");
std::ostream out = outfile;

but dev-cpp give me some error message like this:

variable `std:fstream outfile' has initializer but incomplete type
storage size of `outfile' isn't known

How to correct it ?

Code:

#include <fstream>

• well you need to define a main() function
• get rid of #include <stdio.h>
• #include <fstream>

Ok I was slightly off on previoius. Here is an example:
to console:

Code:

#include <iostream>
#include <fstream>

int main()
{
  std::ofstream outfile ("test.txt");
  std::ostream &out = std::cout;
  out<<"Hello World"<<endl;
}

To file:

Code:

#include <iostream>
#include <fstream>

int main()
{
  std::ofstream outfile ("test.txt");
  std::ostream &out = outfile;
  out<<"Hello World"<<endl;
}

@ Thantos & Tybalt :
THANKS for you quickly helpness.

@ Thantos :

I just copy your code , it's ok:

Code:

#include <iostream>
#include <fstream>
using namespace std;   //I add this statement, otherwise endl cant work;

int main()
{
  std::ofstream outfile ("e:test.txt");   //why add it in main()? 
  std::ostream &out = outfile;
  out<<"Hello World"<<endl;
    
  return 0;          //add this.
}

If I want to save some functions output which no beside in main(),
Whether is it normal work on function , when put this two statements in main() ?

using namespace std; //I add this statement, otherwise endl cant work;

That's because it's std::endl.

Opps yeah I should have had std::endl

The reason I put it into main was because you need a main function to create a program. If you want to do it on a per function base:

Code:

#include <iostream>
#include <fstream>
#include <string>

void foo (std::ostream &, const string &);

int main()
{
  std::ofstream outfile ("test.txt");
  std::string str = "This is a test of the emergency broadcast system";
  foo(std::cout, str);
  foo(outfile, str);
}

void foo (std::ostream &out, const string &str)
{
  out << str << std::endl;
}

To redirect streams, i.e. cout you can do this:

Code:

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

int main()
{
    // Open file for writing
    ofstream output("output.txt");

    // Save existing "cout" buffer
    streambuf* saved_buffer = cout.rdbuf();

    // Redirect "cout" to file stream "output"
    cout.rdbuf(output.rdbuf());

    // Write a line using "cout", this will be redirected to the output file
    cout << "This line will actually go to the output file and not the console." << endl;

    // Restore old "cout" buffer
    cout.rdbuf(saved_buffer);

    // Write a line using "cout", this will be sent to screen as normal
    cout << "This line will go to the console as normal." << endl;

    return 0;
}

After running, using just cout, the file will contain the first line of data while the second line will be displayed to the screen.