What does it mean to write to stdout in C

Question

Does a program that writes to  stdout  write to a file   the screen   I don t understand what it means to write to stdout

User · Answer

stdout is the standard output stream in UNIX   See http   www gnu org software libc manual html node Standard-Streams html Standard-Streams  When running in a terminal  you will see data written to stdout in the terminal and you can redirect it as you choose

User · Answer

stdout stands for standard output stream and it is a stream which is available to your program by the operating system itself  It is already available to your program from the beginning together with stdin and stderr   What they point to  or from  can be anything  actually the stream just provides your program an object that can be used as an interface to send or retrieve data  By default it is usually the terminal but it can be redirected wherever you want  a file  to a pipe goint to another process and so on

User · Answer

stdout is the standard output file stream  Obviously  it s first and default pointer to output is the screen  however you can point it to a file as desired   Please read   http   www cplusplus com reference cstdio stdout   C   is very similar to C however  object oriented

User · Answer

It depends   When you commit to sending output to stdout  you re basically leaving it up to the user to decide where that output should go   If you use printf       or the equivalent fprintf stdout         you re sending the output to stdout  but where that actually ends up can depend on how I invoke your program   If I launch your program from my console like this  I ll see output on my console     prog Hello  World     lt -- output is here on my console   However  I might launch the program like this  producing no output on the console     prog  gt  hello txt   but I would now have a file  hello txt  with the text  Hello  World   inside  thanks to the shell s redirection feature   Who knows     I might even hook up some other device and the output could go there  The point is that when you decide to print to stdout  e g  by using printf     then you won t exactly know where it will go until you see how the process is launched or used

User · Answer

That means that you are printing output on the main output device for the session    whatever that may be  The user s console  a tty session  a file or who knows what  What that device may be varies depending on how the program is being run and from where   The following command will write to the standard output device  stdout      printf   hello world n       Which is just another way  in essence  of doing this     fprintf  stdout   hello world n       In which case stdout is a pointer to a FILE stream that represents the default output device for the application  You could also use  fprintf  stderr   that didn t go well n       in which case you would be sending the output to the standard error output device for the application which may  or may not  be the same as stdout -- as with stdout  stderr is a pointer to a FILE stream representing the default output device for error messages

User · Answer

K Scott Piel wrote a great answer here  but I want to add one important point   Note that the stdout stream is usually line-buffered  so to ensure the output is actually printed and not just left sitting in the buffer waiting to be written you must flush the buffer by either ending your printf statement with a  n  Ex    printf  hello world n      or  printf  hello world     printf   n      or similar  OR you must call fflush stdout   after your printf call   Ex    printf  hello world     fflush stdout     Read more here  Why does printf not flush after the call unless a newline is in the format string

[c] What does it mean to write to stdout in C?

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