std endl vs n

Question

Many C   books contain example code like this     std  cout  lt  lt   Test line   lt  lt  std  endl       so I ve always done that too  But I ve seen a lot of code from working developers like this instead   std  cout  lt  lt   Test line n     Is there a technical reason to prefer one over the other  or is it just a matter of coding style

User · Answer

I ve always had a habit of just using std  endl because it is easy for me to see

User · Answer

There might be performance issues  std  endl forces a flush of the output stream

User · Answer

If you intend to run your program on anything else than your own laptop  never ever use the endl statement  Especially if you are writing a lot of short lines or as I have often seen single characters to a file  The use of endl is know to kill networked file systems like NFS

User · Answer

With reference This is an output-only I O manipulator   std  endl Inserts a newline character into the output sequence os and flushes it as if by calling os put os widen   n    followed by os flush      When to use   This manipulator may be used to produce a line of output immediately    e g       when displaying output from a long-running process  logging activity of multiple threads or logging activity of a program that may crash unexpectedly     Also     An explicit flush of std  cout is also necessary before a call to std  system  if the spawned process performs any screen I O  In most other usual interactive I O scenarios  std  endl is redundant when used with std  cout because any input from std  cin  output to std  cerr  or program termination forces a call to std  cout flush    Use of std  endl in place of   n   encouraged by some sources  may significantly degrade output performance

User · Answer

The std  endl manipulator is equivalent to    n   But std  endl always flushes the stream    std  cout  lt  lt   Test line   lt  lt  std  endl     with flush std  cout  lt  lt   Test line n      no flush

User · Answer

Not a big deal  but endl won t work in boost  lambda    cout lt  lt  1 lt  lt endl  3     error   cout lt  lt  1 lt  lt   n   3     OK   prints 3

User · Answer

The difference can be illustrated by the following   std  cout  lt  lt  std  endl    is equivalent to  std  cout  lt  lt    n   lt  lt  std  flush    So    Use std  endl If you want to force an immediate flush to the output  Use  n if you are worried about performance  which is probably not the case if you are using the  lt  lt  operator     I use  n on most lines  Then use std  endl at the end of a paragraph  but that is just a habit and not usually necessary    Contrary to other claims  the  n character is mapped to the correct platform end of line sequence only if the stream is going to a file  std  cin and std  cout being special but still files  or file-like

User · Answer

If you intend to run your program on anything else than your own laptop  never ever use the endl statement  Especially if you are writing a lot of short lines or as I have often seen single characters to a file  The use of endl is know to kill networked file systems like NFS

User · Answer

I ve always had a habit of just using std  endl because it is easy for me to see

User · Answer

I recalled reading about this in the standard  so here goes   See C11 standard which defines how the standard streams behave  as C   programs interface the CRT  the C11 standard should govern the flushing policy here      ISO IEC 9899 201x      7 21 3   7      At program startup  three text streams are predefined and need not be opened explicitly       standard input  for reading conventional input   standard output  for writing   conventional output   and standard error  for writing diagnostic output   As initially   opened  the standard error stream is not fully buffered  the standard input and standard   output streams are fully buffered if and only if the stream can be determined not to refer   to an interactive device       7 21 3   3      When a stream is unbuffered  characters are intended to appear from the source or at the   destination as soon as possible  Otherwise characters may be accumulated and   transmitted to or from the host environment as a block  When a stream is fully buffered    characters are intended to be transmitted to or from the host environment as a block when   a buffer is filled  When a stream is line buffered  characters are intended to be   transmitted to or from the host environment as a block when a new-line character is   encountered  Furthermore  characters are intended to be transmitted as a block to the host   environment when a buffer is filled  when input is requested on an unbuffered stream  or   when input is requested on a line buffered stream that requires the transmission of   characters from the host environment  Support for these characteristics is   implementation-defined  and may be affected via the setbuf and setvbuf functions    This means that std  cout and std  cin are fully buffered if and only if they are referring to a non-interactive device  In other words  if stdout is attached to a terminal then there is no difference in behavior    However  if std  cout sync with stdio false  is called  then   n  will not cause a flush even to interactive devices  Otherwise   n  is equivalent to std  endl unless piping to files  c   ref on std  endl

User · Answer

If you use Qt and endl  you could accidentally end up using an incorrect endl which gives you very surprising results  See the following code snippet    include  lt iostream gt   include  lt QtCore QtCore gt    include  lt QtGui QtGui gt      notice that there is no  using namespace std   int main int argc  char   argv        QApplication qapp argc argv       QMainWindow mw      mw show        std  cout  lt  lt   Finished Execution    lt  lt  endl         This prints something similar to   Finished Execution 67006AB4      return qapp exec        Note that I wrote endl instead of std  endl  which would have been correct  and apparently there is a endl function defined in qtextstream h  which is part of QtCore    Using   n  instead of endl completely sidesteps any potential namespace issues  This is also a good example why putting symbols into the global namespace  like Qt does by default  is a bad idea

User · Answer

There might be performance issues  std  endl forces a flush of the output stream

User · Answer

The difference can be illustrated by the following   std  cout  lt  lt  std  endl    is equivalent to  std  cout  lt  lt    n   lt  lt  std  flush    So    Use std  endl If you want to force an immediate flush to the output  Use  n if you are worried about performance  which is probably not the case if you are using the  lt  lt  operator     I use  n on most lines  Then use std  endl at the end of a paragraph  but that is just a habit and not usually necessary    Contrary to other claims  the  n character is mapped to the correct platform end of line sequence only if the stream is going to a file  std  cin and std  cout being special but still files  or file-like

User · Answer

The varying line-ending characters don t matter  assuming the file is open in text mode  which is what you get unless you ask for binary   The compiled program will write out the correct thing for the system compiled for   The only difference is that std  endl flushes the output buffer  and   n  doesn t   If you don t want the buffer flushed frequently  use   n    If you do  for example  if you want to get all the output  and the program is unstable   use std  endl

User · Answer

The varying line-ending characters don t matter  assuming the file is open in text mode  which is what you get unless you ask for binary   The compiled program will write out the correct thing for the system compiled for   The only difference is that std  endl flushes the output buffer  and   n  doesn t   If you don t want the buffer flushed frequently  use   n    If you do  for example  if you want to get all the output  and the program is unstable   use std  endl

User · Answer

I ve always had a habit of just using std  endl because it is easy for me to see

User · Answer

They will both write the appropriate end-of-line character s   In addition to that endl will cause the buffer to be committed  You usually don t want to use endl when doing file I O because the unnecessary commits can impact performance

User · Answer

If you use Qt and endl  you could accidentally end up using an incorrect endl which gives you very surprising results  See the following code snippet    include  lt iostream gt   include  lt QtCore QtCore gt    include  lt QtGui QtGui gt      notice that there is no  using namespace std   int main int argc  char   argv        QApplication qapp argc argv       QMainWindow mw      mw show        std  cout  lt  lt   Finished Execution    lt  lt  endl         This prints something similar to   Finished Execution 67006AB4      return qapp exec        Note that I wrote endl instead of std  endl  which would have been correct  and apparently there is a endl function defined in qtextstream h  which is part of QtCore    Using   n  instead of endl completely sidesteps any potential namespace issues  This is also a good example why putting symbols into the global namespace  like Qt does by default  is a bad idea

User · Answer

I recalled reading about this in the standard  so here goes   See C11 standard which defines how the standard streams behave  as C   programs interface the CRT  the C11 standard should govern the flushing policy here      ISO IEC 9899 201x      7 21 3   7      At program startup  three text streams are predefined and need not be opened explicitly       standard input  for reading conventional input   standard output  for writing   conventional output   and standard error  for writing diagnostic output   As initially   opened  the standard error stream is not fully buffered  the standard input and standard   output streams are fully buffered if and only if the stream can be determined not to refer   to an interactive device       7 21 3   3      When a stream is unbuffered  characters are intended to appear from the source or at the   destination as soon as possible  Otherwise characters may be accumulated and   transmitted to or from the host environment as a block  When a stream is fully buffered    characters are intended to be transmitted to or from the host environment as a block when   a buffer is filled  When a stream is line buffered  characters are intended to be   transmitted to or from the host environment as a block when a new-line character is   encountered  Furthermore  characters are intended to be transmitted as a block to the host   environment when a buffer is filled  when input is requested on an unbuffered stream  or   when input is requested on a line buffered stream that requires the transmission of   characters from the host environment  Support for these characteristics is   implementation-defined  and may be affected via the setbuf and setvbuf functions    This means that std  cout and std  cin are fully buffered if and only if they are referring to a non-interactive device  In other words  if stdout is attached to a terminal then there is no difference in behavior    However  if std  cout sync with stdio false  is called  then   n  will not cause a flush even to interactive devices  Otherwise   n  is equivalent to std  endl unless piping to files  c   ref on std  endl

User · Answer

There might be performance issues  std  endl forces a flush of the output stream

User · Answer

The varying line-ending characters don t matter  assuming the file is open in text mode  which is what you get unless you ask for binary   The compiled program will write out the correct thing for the system compiled for   The only difference is that std  endl flushes the output buffer  and   n  doesn t   If you don t want the buffer flushed frequently  use   n    If you do  for example  if you want to get all the output  and the program is unstable   use std  endl

User · Answer

There s another function call implied in there if you re going to use std  endl  a  std  cout  lt  lt   Hello n   b  std  cout  lt  lt   Hello   lt  lt  std  endl    a  calls operator  lt  lt  once   b  calls operator  lt  lt  twice

User · Answer

There might be performance issues  std  endl forces a flush of the output stream

User · Answer

They will both write the appropriate end-of-line character s   In addition to that endl will cause the buffer to be committed  You usually don t want to use endl when doing file I O because the unnecessary commits can impact performance

User · Answer

The varying line-ending characters don t matter  assuming the file is open in text mode  which is what you get unless you ask for binary   The compiled program will write out the correct thing for the system compiled for   The only difference is that std  endl flushes the output buffer  and   n  doesn t   If you don t want the buffer flushed frequently  use   n    If you do  for example  if you want to get all the output  and the program is unstable   use std  endl

User · Answer

The difference can be illustrated by the following   std  cout  lt  lt  std  endl    is equivalent to  std  cout  lt  lt    n   lt  lt  std  flush    So    Use std  endl If you want to force an immediate flush to the output  Use  n if you are worried about performance  which is probably not the case if you are using the  lt  lt  operator     I use  n on most lines  Then use std  endl at the end of a paragraph  but that is just a habit and not usually necessary    Contrary to other claims  the  n character is mapped to the correct platform end of line sequence only if the stream is going to a file  std  cin and std  cout being special but still files  or file-like

User · Answer

There s another function call implied in there if you re going to use std  endl  a  std  cout  lt  lt   Hello n   b  std  cout  lt  lt   Hello   lt  lt  std  endl    a  calls operator  lt  lt  once   b  calls operator  lt  lt  twice

User · Answer

The std  endl manipulator is equivalent to    n   But std  endl always flushes the stream    std  cout  lt  lt   Test line   lt  lt  std  endl     with flush std  cout  lt  lt   Test line n      no flush

User · Answer

They will both write the appropriate end-of-line character s   In addition to that endl will cause the buffer to be committed  You usually don t want to use endl when doing file I O because the unnecessary commits can impact performance

User · Answer

The difference can be illustrated by the following   std  cout  lt  lt  std  endl    is equivalent to  std  cout  lt  lt    n   lt  lt  std  flush    So    Use std  endl If you want to force an immediate flush to the output  Use  n if you are worried about performance  which is probably not the case if you are using the  lt  lt  operator     I use  n on most lines  Then use std  endl at the end of a paragraph  but that is just a habit and not usually necessary    Contrary to other claims  the  n character is mapped to the correct platform end of line sequence only if the stream is going to a file  std  cin and std  cout being special but still files  or file-like

User · Answer

With reference This is an output-only I O manipulator   std  endl Inserts a newline character into the output sequence os and flushes it as if by calling os put os widen   n    followed by os flush      When to use   This manipulator may be used to produce a line of output immediately    e g       when displaying output from a long-running process  logging activity of multiple threads or logging activity of a program that may crash unexpectedly     Also     An explicit flush of std  cout is also necessary before a call to std  system  if the spawned process performs any screen I O  In most other usual interactive I O scenarios  std  endl is redundant when used with std  cout because any input from std  cin  output to std  cerr  or program termination forces a call to std  cout flush    Use of std  endl in place of   n   encouraged by some sources  may significantly degrade output performance

User · Answer

I ve always had a habit of just using std  endl because it is easy for me to see

User · Answer

Not a big deal  but endl won t work in boost  lambda    cout lt  lt  1 lt  lt endl  3     error   cout lt  lt  1 lt  lt   n   3     OK   prints 3

User · Answer

They will both write the appropriate end-of-line character s   In addition to that endl will cause the buffer to be committed  You usually don t want to use endl when doing file I O because the unnecessary commits can impact performance

[c++] "std::endl" vs "\n"

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