Named Pipes are useful in Inter Process communication. Pipes will always have two ends. One on the Server (usually to listen and reply) and the client which connects and sends messages. So Pipes can be used in communicating among two programs very conveniently.
Named Pipe server can be created using CreateNamedPipe function. This function creates the pipe and returns a handle for the Pipe created. Then ConnectNamedPipe should be used to listen for any incoming connections from the client. Typically this waits in a infinite loops to keep receiving messages.
The following sample uses both CreateNamedPipe and ConnectNamedPipe to receive and print the messages. See the corresponding Named Pipe client.
CreateNamedPipe – Sample:
#include <windows.h>
#include <stdio.h>
#define BUFSIZE 1024
#define PIPE_TIMEOUT 5000
int main()
{
BOOL fConnected;
LPTSTR lpszPipename = "\\\\.\\pipe\\SamplePipe";
CHAR chRequest[BUFSIZE]; DWORD cbBytesRead;
BOOL fSuccess;
HANDLE hPipe;
hPipe = CreateNamedPipe ( lpszPipename, PIPE_ACCESS_DUPLEX, // read/write access PIPE_TYPE_MESSAGE | // message type pipe PIPE_READMODE_MESSAGE | // message-read mode PIPE_WAIT, // blocking mode PIPE_UNLIMITED_INSTANCES, // max. instances BUFSIZE, // output buffer size BUFSIZE, // input buffer size PIPE_TIMEOUT, // client time-out NULL); // no security attribute
if (hPipe == INVALID_HANDLE_VALUE)
return true;
for (;;)
{
// Trying connectnamedpipe in sample for CreateNamedPipe
// Wait for the client to connect; if it succeeds,
// the function returns a nonzero value. If the function returns
// zero, GetLastError returns ERROR_PIPE_CONNECTED.
fConnected = ConnectNamedPipe(hPipe, NULL) ? TRUE : (GetLastError() == ERROR_PIPE_CONNECTED);
if (fConnected)
{
fSuccess = ReadFile (hPipe, // handle to pipe
chRequest, // buffer to receive data
BUFSIZE, // size of buffer
&cbBytesRead, // number of bytes read
NULL);
// not overlapped I/O
chRequest[cbBytesRead] = '\0';
printf("Data Received: %s\n",chRequest);
if (! fSuccess || cbBytesRead == 0)
break;
FlushFileBuffers(hPipe);
DisconnectNamedPipe(hPipe);
}
else
// The client could not connect in the CreateNamedPipe sample, so close the pipe.
CloseHandle(hPipe);
}
CloseHandle(hPipe);
return 1;
}
//End of sample using CreateNamedPipe
The above program waits infinitely for Client Pipes to connect from \\.\pipe\SamplePipe. When a client is connected and data is received, it is printed on to the console.