C++ Understanding Buffer and std::endl [duplicate] - c++

Question

This question already has answers here:
"std::endl" vs "\n"
(10 answers)
Closed 1 year ago.
I am trying to understand buffer, endl vs \n and why the latter is more efficient than endl.
Specifically, I am reading this
https://www.geeksforgeeks.org/buffer-flush-means-c/
The following code is supposedly output 1,2,3,4,5 at once
#include <iostream>
#include <windows.h>
using namespace std;
int main()
{
for (int i = 1; i <= 5; ++i)
{
cout << i << " " ;
Sleep(300);
}
cout << endl;
return 0;
}
whereas the following will output each integer one at a time:
#include <iostream>
#include <windows.h>
using namespace std;
int main()
{
for (int i = 1; i <= 5; ++i)
{
cout << i << " " << flush;
Sleep(300);
}
return 0;
}
However, both looks exactly the same during the time of execution, they appear one a time. Is my understanding wrong?
I'm also confused why endl is less efficient compared to \n.
From what I read, endl adds a \n and then flushes.
Isn't this more efficient, since it waits for the buffer to be full then output everything at once, compared to \n?
Please correct my flawed understanding, thank you.

Answer 1

You will clearly see the difference if you run the following code:
#include <iostream>
#include <unistd.h>
using namespace std;
int main()
{
for (int i = 1; i <= 5; ++i)
{
cout << i << " " << flush;
usleep(300000);
}
cout<<"\n";
for (int i = 1; i <= 5; ++i)
{
cout << i << " " ;
usleep(300000);
}
cout << endl;
return 0;
}
std::endl is equivalent to using "\n" and flush together.
If your program is stable then simply use "\n" else go for std::endl. "\n" is more efficient in terms that it does not force the buffer to be flushed right then.
Also in your code, you might now be able to see the difference because you are using Sleep() which takes input in milisec, so try with greater value.