WaitCommEvent and GetCommMask (and overlapping)

[AnotherProgrammer]

Thanks for the help on my earlier problem.. I have now undertaken rewriting the serial portion of my code to use CreateFile and the like. It's all a bit complicated though, and being new to this, I have a few questions. It starts with overlapping, and also involves WaitCommEvent and GetCommMask. I did a search on the topics and read a few articles that were found, but while they cleared a few things up, they still left me with a few questions unanswered. First, I understand that SetCommMask allows you to screen for only a few of the events. But after calling SetCommMask to look for only what you want, how does one screen for these events and process them appropriately? I know you can use WaitCommEvent, but in that case, why would you even need GetCommMask? I also need to use overlapping for this program, but I'm not sure how to implement it or even what it actually is (do I need to use the overlapped structure at all?). I was able to find this piece of example code on MSDN: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/devio/base/monitoring\_communications\_events.asp I do not fully understand how it operates, though. Also, this article was very helpful, to a point: http://www.codeproject.com/system/serial\_com.asp Where I got lost was the huge block of code where he uses the OVERLAPPED structure and the Threadfn function, after which he writes "If you understood the above code , you will understand the whole of this article and the source code provided." Gulp. As always, the help is very much appreciated.

[AnotherProgrammer]

From this link: Configuring a communications resource: #include int main(int argc, char *argv[]) { DCB dcb; HANDLE hCom; BOOL fSuccess; char *pcCommPort = "COM2"; hCom = CreateFile( pcCommPort, GENERIC_READ | GENERIC_WRITE, 0, // must be opened with exclusive-access NULL, // no security attributes OPEN_EXISTING, // must use OPEN_EXISTING 0, // not overlapped I/O NULL // hTemplate must be NULL for comm devices ); pcCommPort is declared as a pointer to a character, which is assigned "COM2". How does this make sense? A char cannot be more than one character in length, right? Upon testing, trying to do *pcCommPort = "COM3" later in the program does indeed yield "error C2440: '=' : cannot convert from 'char [5]' to 'char'" which actually makes sense. So why is that same assignment statement allowed upon declaration? Also, if at some point, I need to change the COM port to say, COM3, how would I accomplish that? *pcCommPort = "COM3" did not work, as I mentioned. Thanks in advance.

[Paul Ranson]

"COM2" is a constant null terminated string allocated somewhere by the compiler. It's reasonable to set a char * to point to its first character. But really it should be a const char * since the value of the string should not be changed. Try writing pcCommPort = "COM3", now you're setting the value of pcCommPort to the address of "COM3". Previously you were trying to set what pcCommPort pointed at (in this case presumably the constant string "COM2") to your new string. Which isn't what you intended. Paul

[AnotherProgrammer]

Thanks Paul -- that was it! I don't know why I didn't catch it myself. Still looking for some clarification and answers about my original post... your help is greatly appreciated.

[AnotherProgrammer]

I'm now down to the point where I have the code written for everything up to where I understand -- meaning, the WaitCommEvent part is the only part that needs completing. Any help with this?