Buffering in standard library in C/C++

Question

I have a question about the buffering in standard library for I/O: I read "The Linux Programming Interface" chapter 13 about File I/O buffering, the author mentioned that standard library used I/O buffering for disk file and terminal. My question is that does this I/O buffering also apply to FIFO, pipe, socket and network file?

Answer 1

Yes, if you're using the FILE * based standard I/O library. The only odd thing that might happen is if the underlying system file descriptor returns non-zero for the isatty function. Then stdio might 'line buffer' both input and output. This means it tends to flush when it sees a '\\n' .

I believe that it's required to line buffer stdout if file descriptor 1 returns non-zero for isatty .

Answer 2

No. Anything that's an ordinary file descriptor (such as those returned by open(2) , pipe(2) , socket(2) , and accept(2) ) is not buffered—any data you read or write to it is input or output immediately via direct system calls.

Buffering only happens when you have FILE* objects, which you can get by fopen(3) 'ing a regular disk file; the objects stdin , stdout , and stderr are also FILE* objects that are setup at program start. Buffering is usually enabled on FILE* objects, but not always—it can be disabled with setbuf(3) , and stderr is unbuffered by default.

If you want to create a buffered stream out of a regular file descriptor, you can do so with fdopen(3) .