Create Windows named pipe in C++

Question

I am trying to create a simple communication between 2 processes in C++ (Windows) like FIFO in Linux.

This is my server:

int main()
{
    HANDLE pipe = CreateFile(TEXT("\\\\.\\pipe\\Pipe"), GENERIC_READ, 0, NULL, OPEN_EXISTING,    FILE_FLAG_OVERLAPPED, NULL);
    ConnectNamedPipe(pipe, NULL);
    while(TRUE){
        string data;
        DWORD numRead =1 ;
        ReadFile(pipe, &data, 1024, &numRead, NULL);
        cout << data << endl;

}
    CloseHandle(pipe);
    return 0;
}

And this is my client:

int main()
{
    HANDLE pipe = CreateFile(TEXT("\\\\.\\pipe\\Pipe"), GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);
    ConnectNamedPipe(pipe, NULL);
    string message = "TEST";
    DWORD numWritten;
    WriteFile(pipe, message.c_str(), message.length(), &numWritten, NULL);
    return 0;
}

The code doesn't work. How can I fix it to work like FIFO?

Answer 1

You cannot create a named pipe by calling CreateFile(..).

Have a look at the pipe examples of the Microsoft Learn. Since these examples are quite complex I've quickly written a VERY simple named pipe server and client.

int main(void)
{
    HANDLE hPipe;
    char buffer[1024];
    DWORD dwRead;


    hPipe = CreateNamedPipe(TEXT("\\\\.\\pipe\\Pipe"),
                            PIPE_ACCESS_DUPLEX,
                            PIPE_TYPE_BYTE | PIPE_READMODE_BYTE | PIPE_WAIT,   // FILE_FLAG_FIRST_PIPE_INSTANCE is not needed but forces CreateNamedPipe(..) to fail if the pipe already exists...
                            1,
                            1024 * 16,
                            1024 * 16,
                            NMPWAIT_USE_DEFAULT_WAIT,
                            NULL);
    while (hPipe != INVALID_HANDLE_VALUE)
    {
        if (ConnectNamedPipe(hPipe, NULL) != FALSE)   // wait for someone to connect to the pipe
        {
            while (ReadFile(hPipe, buffer, sizeof(buffer) - 1, &dwRead, NULL) != FALSE)
            {
                /* add terminating zero */
                buffer[dwRead] = '\0';

                /* do something with data in buffer */
                printf("%s", buffer);
            }
        }

        DisconnectNamedPipe(hPipe);
    }

    return 0;
}

And here is the client code:

int main(void)
{
    HANDLE hPipe;
    DWORD dwWritten;


    hPipe = CreateFile(TEXT("\\\\.\\pipe\\Pipe"), 
                       GENERIC_READ | GENERIC_WRITE, 
                       0,
                       NULL,
                       OPEN_EXISTING,
                       0,
                       NULL);
    if (hPipe != INVALID_HANDLE_VALUE)
    {
        WriteFile(hPipe,
                  "Hello Pipe\n",
                  12,   // = length of string + terminating '\0' !!!
                  &dwWritten,
                  NULL);

        CloseHandle(hPipe);
    }

    return (0);
}

You should replace the name of the pipe TEXT("\\\\.\\pipe\\Pipe") by a #define which is located in a commonly used header file.