WinAPI C++ client detect write on anonymous pipe before reading

Question

I am writing a C++ (Windows) client console application which reads from an anonymous pipe on STDIN. I would like to be able to use my program as follows:

echo i         


        

Answer 1

Look at PeekNamedPipe(). Despite its name, it works for both named and anonymous pipes.

int main(int argc, const char *argv[])
{
    char char_buffer[BUFSIZE]; 
    DWORD bytes_read;
    DWORD bytes_avail;
    DWORD dw;
    HANDLE stdin_handle;
    bool is_pipe;

    stdin_handle = GetStdHandle(STD_INPUT_HANDLE);
    is_pipe = !GetConsoleMode(stdin_handle, &dw);

    if (stdin_handle == INVALID_HANDLE_VALUE) {
        std::cout << "Error: invalid handle value!\n\n";
    } else {
        while (1) { 
            if (is_pipe) {
                if (PeekNamedPipe(stdin_handle, NULL, 0, NULL, &bytes_avail, NULL)) {
                    if (bytes_avail == 0) {
                        Sleep(100);
                        continue;
                    }
                }
            }

            if (!ReadFile(stdin_handle, char_buffer, min(bytes_avail, BUFSIZE), &bytes_read, NULL)) {
                break; 
            }

            if (bytes_read == 0) {
                break;
            }

            // Output what we have read so far
            for (unsigned int i = 0; i < bytes_read; i++) {
                std::cout << char_buffer[i];
            }
        }
    }

    return 0;
}