Programming

thanks

but i still have some doubts!
that is where does the printf save it's buffer and how does the buffer being copied?
does the process save it's buffer in it's struct user?or in it's data area?

and how does the OS know it's line-buffered or block-buffered?
Is there a flag in it?

By defalt stdout is "line - buffered".
It mean that after printf("...\n") buffer was flushed if output to stdout.

Certainly the file I/O buffers isn't "line-buffered", and before fork(), buffers was not flushed. So its filled buffers was copied.

What happen if we write " for(int i = 0 ; i < 3; ++i) " ?

You can manage I/O buffering by using "setvbuf" function.

Do you mean when OS invoke printf(),it will invoke setbuf()?

and does it mean that setbuf() will set a buffer flag to determine
if it is line-buffered or block-buffered?


i have traced in C++ code when it invoke setbuf(),but i still can't find where it set flag?

i wanna thank all the people who reply to my question!!!

No, it only mean that you can change default behaviour of I/O buffering.

After "printf" call, all data come in I/O buffer. In first case it is standard output (stdout) buffer, which is "line - buffered".
In another case it is file I/O buffer, which is "block - buffered".

I hope that answered your question.