How to redirect stdin from my app to another knowing its PID (C,in windows)

Question

I have a script vbs wich redirect some data to the stdin of myApp (written in C in Windows). If myApp was already launched before myApp finds the PID of the first myApp session and redirects the input received via stdin to the stdin of the first session of myApp which handles the stdin. So when myApp receives a stdin and no other instances of myApp are running it handles the stdin and does stuff with it. So the question is : how to redirect stdin from an app to another knowing the PID of this secnd spp? language = C platform = MSwindows

Answer 1

Is this any use to you? http://msdn.microsoft.com/en-us/library/ms682499%28VS.85%29.aspx

This article creates a child process with re-directed IO using anonymous pipes, you could use named pipes. Using this function: http://msdn.microsoft.com/en-us/library/aa365144%28VS.85%29.aspx you can test if a named pipe already exists - if it doesn't, you can create one and wait on its input.

I'm not sure r.e. multiple files writing to the same named pipe - I assume all the data comes through as if one file, so I'd use one named pipe as a negotiator which instantiates a new named pipe per client and adds its pipe to the list of pipes to wait on. Close it with a message through the new pipe.

I don't think (someone correct me if I'm wrong please) it is that easy to redirect handles of another process.

Answer 2

thanx for the quick reply. But what I need is that the 2 processes are completely independend. The parent code in your example creates a child process, mine should only check if another instance of the same process is already running. In that case this second instance should redirect the received stdin to THAT first instance (via its PID) and close itself (not the first intance). The first instance will always be running and waiting for the stdin given by other instances of the same process.

Answer 3

Ok having the chance of writing the source of the program I'll move toward the idea of named pipes. The main process of App1 will check if another instance of App (i.e. App0) is already running. If so the stdin received by App1 will be redirected to a named pipe X. App0 keeps receiving inputs using the named pipe X. So App0 and all others instances of App (App2,e,4...) will communicate via the named pipe. Thankyou very much NineFingers, u were so helpful!

Answer 4

No problem Gino!