Confused about the default buffer size of stdout

#include<iostream>

using namespace std;

int main()

{

    for(int i = 0 ; i < 10; i++)

    {

       printf("1 ");

    }

    while(1);

}

Is stdout use line buffered in default? If so, we will not see ten 1 on the console when execute the code above. What confused me is:

On windows system with gcc: the 1 is printed immediately.

On ubuntu system with gcc: the 1 is not printed.

I use cout<<stdout->_bufsiz to check the buffer size on windows, it is 0, does it mean that the stdout on windows is unbuffered in default?

cout<<stdout->_bufsiz is not work on ubuntu, how can I get the buffer size of stdout ?

When I replace while(1); with getchar();, 1 is printed immediately both on windows and ubuntu, why? getchar(); flush the stdout buffer ?

Thanks.

edited May 13 '14 at 13:38

asked May 13 '14 at 13:15

tenos

3961513

The variable stdout have nothing to do with std::cout. The stdout variable is used by the old C functions like printf, while the C++ streams uses their own buffers. There is no way of getting the buffer size of the underlying basic_streambuf used by C++ streams.

– Some programmer dude
May 13 '14 at 13:19

I replace cin with printf, it is still the same problem. @JoachimPileborg

– tenos
May 13 '14 at 13:32

add a comment |

#include<iostream>

using namespace std;

int main()

{

    for(int i = 0 ; i < 10; i++)

    {

       printf("1 ");

    }

    while(1);

}

Is stdout use line buffered in default? If so, we will not see ten 1 on the console when execute the code above. What confused me is:

On windows system with gcc: the 1 is printed immediately.

On ubuntu system with gcc: the 1 is not printed.

I use cout<<stdout->_bufsiz to check the buffer size on windows, it is 0, does it mean that the stdout on windows is unbuffered in default?

cout<<stdout->_bufsiz is not work on ubuntu, how can I get the buffer size of stdout ?

When I replace while(1); with getchar();, 1 is printed immediately both on windows and ubuntu, why? getchar(); flush the stdout buffer ?

Thanks.

edited May 13 '14 at 13:38

asked May 13 '14 at 13:15

tenos

3961513

The variable stdout have nothing to do with std::cout. The stdout variable is used by the old C functions like printf, while the C++ streams uses their own buffers. There is no way of getting the buffer size of the underlying basic_streambuf used by C++ streams.

– Some programmer dude
May 13 '14 at 13:19

I replace cin with printf, it is still the same problem. @JoachimPileborg

– tenos
May 13 '14 at 13:32

add a comment |

#include<iostream>

using namespace std;

int main()

{

    for(int i = 0 ; i < 10; i++)

    {

       printf("1 ");

    }

    while(1);

}

Is stdout use line buffered in default? If so, we will not see ten 1 on the console when execute the code above. What confused me is:

On windows system with gcc: the 1 is printed immediately.

On ubuntu system with gcc: the 1 is not printed.

I use cout<<stdout->_bufsiz to check the buffer size on windows, it is 0, does it mean that the stdout on windows is unbuffered in default?

cout<<stdout->_bufsiz is not work on ubuntu, how can I get the buffer size of stdout ?

When I replace while(1); with getchar();, 1 is printed immediately both on windows and ubuntu, why? getchar(); flush the stdout buffer ?

Thanks.

edited May 13 '14 at 13:38

asked May 13 '14 at 13:15

tenos

3961513

#include<iostream>

using namespace std;

int main()

{

    for(int i = 0 ; i < 10; i++)

    {

       printf("1 ");

    }

    while(1);

}

Is stdout use line buffered in default? If so, we will not see ten 1 on the console when execute the code above. What confused me is:

On windows system with gcc: the 1 is printed immediately.

On ubuntu system with gcc: the 1 is not printed.

I use cout<<stdout->_bufsiz to check the buffer size on windows, it is 0, does it mean that the stdout on windows is unbuffered in default?

cout<<stdout->_bufsiz is not work on ubuntu, how can I get the buffer size of stdout ?

When I replace while(1); with getchar();, 1 is printed immediately both on windows and ubuntu, why? getchar(); flush the stdout buffer ?

Thanks.

c++ io buffer stdout

edited May 13 '14 at 13:38

asked May 13 '14 at 13:15

tenos

3961513

edited May 13 '14 at 13:38

asked May 13 '14 at 13:15

tenos

3961513

edited May 13 '14 at 13:38

asked May 13 '14 at 13:15

tenos

3961513

asked May 13 '14 at 13:15

tenos

3961513

asked May 13 '14 at 13:15

tenos

3961513

The variable stdout have nothing to do with std::cout. The stdout variable is used by the old C functions like printf, while the C++ streams uses their own buffers. There is no way of getting the buffer size of the underlying basic_streambuf used by C++ streams.

– Some programmer dude
May 13 '14 at 13:19

I replace cin with printf, it is still the same problem. @JoachimPileborg

– tenos
May 13 '14 at 13:32

add a comment |

The variable stdout have nothing to do with std::cout. The stdout variable is used by the old C functions like printf, while the C++ streams uses their own buffers. There is no way of getting the buffer size of the underlying basic_streambuf used by C++ streams.

– Some programmer dude
May 13 '14 at 13:19

I replace cin with printf, it is still the same problem. @JoachimPileborg

– tenos
May 13 '14 at 13:32

The variable stdout have nothing to do with std::cout. The stdout variable is used by the old C functions like printf, while the C++ streams uses their own buffers. There is no way of getting the buffer size of the underlying basic_streambuf used by C++ streams.

– Some programmer dude
May 13 '14 at 13:19

I replace cin with printf, it is still the same problem. @JoachimPileborg

– tenos
May 13 '14 at 13:32

add a comment |

2 Answers
2

active

oldest

votes

The question is, which buffer do you mean?

the ostream buffer?

the buffer of the file stream under the STDOUT file descriptor?

the buffer beneath that in whatever device STDOUT happens to be built on?

If it's 1 I think you're doing the right thing.

If it's 2, then you're out of luck. see the documentation of setbuf() here http://man7.org/linux/man-pages/man3/setbuf.3.html as far as I know there is no getbuf equivalent. (can someone correct me here?)

If it's 3 then I think you're really out of luck.

answered May 13 '14 at 13:41

Richard Hodges

56.7k658104

I mean the stdout buffer when I call printf

– tenos
May 13 '14 at 13:48

add a comment |

On linux you can do these to flush the buffer :

cout << "1 " << "n";

cout << "1 " << flush;

answered May 13 '14 at 13:19

AMDG

783821

1

that doesn't answer the question

– spiritwolfform
May 13 '14 at 13:26

The first comment on the question answer it. Here I add a work around for Linux.

– AMDG
May 13 '14 at 13:28

cout<<"n" doesn't flush the buffer. cout<<endl does. And you didn't answer my qustion @AMDG

– tenos
May 13 '14 at 13:43

add a comment |

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

The question is, which buffer do you mean?

the ostream buffer?

the buffer of the file stream under the STDOUT file descriptor?

the buffer beneath that in whatever device STDOUT happens to be built on?

If it's 1 I think you're doing the right thing.

If it's 3 then I think you're really out of luck.

answered May 13 '14 at 13:41

Richard Hodges

56.7k658104

I mean the stdout buffer when I call printf

– tenos
May 13 '14 at 13:48

add a comment |

The question is, which buffer do you mean?

the ostream buffer?

the buffer of the file stream under the STDOUT file descriptor?

the buffer beneath that in whatever device STDOUT happens to be built on?

If it's 1 I think you're doing the right thing.

If it's 3 then I think you're really out of luck.

answered May 13 '14 at 13:41

Richard Hodges

56.7k658104

I mean the stdout buffer when I call printf

– tenos
May 13 '14 at 13:48

add a comment |

The question is, which buffer do you mean?

the ostream buffer?

the buffer of the file stream under the STDOUT file descriptor?

the buffer beneath that in whatever device STDOUT happens to be built on?

If it's 1 I think you're doing the right thing.

If it's 3 then I think you're really out of luck.

answered May 13 '14 at 13:41

Richard Hodges

56.7k658104

The question is, which buffer do you mean?

the ostream buffer?

the buffer of the file stream under the STDOUT file descriptor?

the buffer beneath that in whatever device STDOUT happens to be built on?

If it's 1 I think you're doing the right thing.

If it's 3 then I think you're really out of luck.

answered May 13 '14 at 13:41

Richard Hodges

56.7k658104

answered May 13 '14 at 13:41

Richard Hodges

56.7k658104

answered May 13 '14 at 13:41

Richard Hodges

56.7k658104

answered May 13 '14 at 13:41

Richard Hodges

56.7k658104

I mean the stdout buffer when I call printf

– tenos
May 13 '14 at 13:48

add a comment |

I mean the stdout buffer when I call printf

– tenos
May 13 '14 at 13:48

I mean the stdout buffer when I call printf

– tenos
May 13 '14 at 13:48

add a comment |

On linux you can do these to flush the buffer :

cout << "1 " << "n";

cout << "1 " << flush;

answered May 13 '14 at 13:19

AMDG

783821

1

that doesn't answer the question

– spiritwolfform
May 13 '14 at 13:26

The first comment on the question answer it. Here I add a work around for Linux.

– AMDG
May 13 '14 at 13:28

cout<<"n" doesn't flush the buffer. cout<<endl does. And you didn't answer my qustion @AMDG

– tenos
May 13 '14 at 13:43

add a comment |

On linux you can do these to flush the buffer :

cout << "1 " << "n";

cout << "1 " << flush;

answered May 13 '14 at 13:19

AMDG

783821

1

that doesn't answer the question

– spiritwolfform
May 13 '14 at 13:26

The first comment on the question answer it. Here I add a work around for Linux.

– AMDG
May 13 '14 at 13:28

cout<<"n" doesn't flush the buffer. cout<<endl does. And you didn't answer my qustion @AMDG

– tenos
May 13 '14 at 13:43

add a comment |

On linux you can do these to flush the buffer :

cout << "1 " << "n";

cout << "1 " << flush;

answered May 13 '14 at 13:19

AMDG

783821

On linux you can do these to flush the buffer :

cout << "1 " << "n";

cout << "1 " << flush;

answered May 13 '14 at 13:19

AMDG

783821

answered May 13 '14 at 13:19

AMDG

783821

answered May 13 '14 at 13:19

AMDG

783821

answered May 13 '14 at 13:19

AMDG

783821

1

that doesn't answer the question

– spiritwolfform
May 13 '14 at 13:26

The first comment on the question answer it. Here I add a work around for Linux.

– AMDG
May 13 '14 at 13:28

cout<<"n" doesn't flush the buffer. cout<<endl does. And you didn't answer my qustion @AMDG

– tenos
May 13 '14 at 13:43

add a comment |

1

that doesn't answer the question

– spiritwolfform
May 13 '14 at 13:26

The first comment on the question answer it. Here I add a work around for Linux.

– AMDG
May 13 '14 at 13:28

cout<<"n" doesn't flush the buffer. cout<<endl does. And you didn't answer my qustion @AMDG

– tenos
May 13 '14 at 13:43

that doesn't answer the question

– spiritwolfform
May 13 '14 at 13:26

The first comment on the question answer it. Here I add a work around for Linux.

– AMDG
May 13 '14 at 13:28

cout<<"n" doesn't flush the buffer. cout<<endl does. And you didn't answer my qustion @AMDG

– tenos
May 13 '14 at 13:43

add a comment |

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