In C/C++ I want to write to the same pipe multiple times

Question

I have a program that creates pipes between two processes. One process constantly monitors the output of the other and when specific output is encountered it gives input through the other pipe with the write() function. The problem I am having, though is that the contents of the pipe don't go through to the other process's stdin stream until I close() the pipe. I want this program to infinitely loop and react every time it encounters the output it is looking for. Is there any way to send the input to the other process without closing the pipe?

I have searched a bit and found that named pipes can be reopened after closing them, but I wanted to find out if there was another option since I have already written the code to use unnamed pipes and I haven't yet learned to use named pipes.

Answer 1

看看使用fflush 。

Answer 2

How are you reading the other end? Are you expecting complete strings? You aren't sending terminating NULs in the snippet you posted. Perhaps sending strlen(string)+1 bytes will fix it. Without seeing the code it's hard to tell.

Answer 3

Use fsync. http://pubs.opengroup.org/onlinepubs/007908799/xsh/fsync.html

From http://www.delorie.com/gnu/docs/glibc/libc_239.html : Once write returns, the data is enqueued to be written and can be read back right away, but it is not necessarily written out to permanent storage immediately. You can use fsync when you need to be sure your data has been permanently stored before continuing. (It is more efficient for the system to batch up consecutive writes and do them all at once when convenient. Normally they will always be written to disk within a minute or less.) Modern systems provide another function fdatasync which guarantees integrity only for the file data and is therefore faster. You can use the O_FSYNC open mode to make write always store the data to disk before returning.