C / C++ / MFC

Re: How to open and read/write from multiple serial ports at the same time?

17-Jul-11 20:42

Hi all,

i am using CreateFile to open the port,its working fine when i am handle this with only single port.

but now i want to open multiple port at the same time and perform read/write operation on these ports.

In The open port method, it opens the first available port and when it gets the second it closes the opened one and then opens the next port and so on.

if (IsOpen())
  {
    //Close down the comms port
    BOOL bSuccess = CloseHandle(m_hComm);
    m_hComm = INVALID_HANDLE_VALUE;
    if (!bSuccess)
      TRACE(_T("Failed to close up the comms port, GetLastError:%d\n"), GetLastError());
  }
  
  //Free the event object we are using
  if (m_hEvent)
  {
    CloseHandle(m_hEvent);
    m_hEvent = NULL;
  }

//Call CreateFile to open up the comms port
  CString sPort;
  sPort.Format(_T("\\\\.\\COM%d"), nPort);
  m_hComm = CreateFile(sPort, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, NULL);

so please help me how can i do this.

thanks in advance.

Code-o-mat17-Jul-11 20:50

Re: How to open and read/write from multiple serial ports at the same time?

17-Jul-11 20:50

Are you possibly using the same instance of this class to open all your ports?

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> //TODO: Implement signature here<

Le@rner17-Jul-11 20:56

Re: How to open and read/write from multiple serial ports at the same time?

17-Jul-11 20:56

i am using it like this:

//CPort_Class handels all port operation like open/Close and read and write

//CAppClass its a main appclass

void CAppClass::fun1()
{
  for(int i=0; i<port_count;i++)
  {
    CPort_Class* p_c=new CPort_Class;
    p_c->Open()
   
    //some working

    p_c->Close();
  }
}

Code-o-mat17-Jul-11 21:36

Re: How to open and read/write from multiple serial ports at the same time?

17-Jul-11 21:36

This code opens a port and then later on closes it before going on with the next one. I thought you wanted to have multiple ports open at the same time. Could you clearify?

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> //TODO: Implement signature here<

Le@rner17-Jul-11 21:38

Re: How to open and read/write from multiple serial ports at the same time?

17-Jul-11 21:38

yes i want to open the multiple port at same time.

Code-o-mat17-Jul-11 21:52

Re: How to open and read/write from multiple serial ports at the same time?

17-Jul-11 21:52

The code fragment you have shown opens and closes the ports one-by-one. You should rethink your strategy i guess. Without knowing more about what exactly you are trying to achieve it is hard to guess on anything, but you could for example try strating a new thread for each port if there aren't too many ports you want to use (of course you would need to implement proper synchronization as needed), or you could have an array for the port class instances, something like this:

CPort_Class *ports = new CPort_Class[portcount]
for (int port = 0; port < portcount; port++) ports[port].Open();
...
//now you have an array of ports that are opened simulteniously, do what you need with them
...
for (int port = 0; port < portcount; port++) ports[port].Close(); //you could put a call to Close() in
                                                                  //the destructor of this class possibly
delete []ports;

This is a simplified code fragment, you would of course need to do error checks too.

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> //TODO: Implement signature here<

Le@rner17-Jul-11 22:05

Re: How to open and read/write from multiple serial ports at the same time?

17-Jul-11 22:05

now i am crate different thread for each port,now how can i do this?

Code-o-mat17-Jul-11 22:35

17-Jul-11 22:35

If you don't know threading then you have a lot to learn. There are great articles about threading all around the web so google away. But if you do not know threading yet then maybe the other solution would be better for you, but as said, since i do not know what you are trying to achieve, it is hard to say.

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> //TODO: Implement signature here<

Message Removed

16-Dec-11 0:14

Re: How to open and read/write from multiple serial ports at the same time?

16-Dec-11 0:14

Message Removed

Code-o-mat16-Dec-11 0:29

16-Dec-11 0:29

You are probably specifying it an invalid handle or the instance of which you are trying to use its m_hComm member has been deleted OR it never existed at all and you are calling into some random pointer.

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> If it doesn't matter, it's antimatter.<

array declaration

Danzy8317-Jul-11 10:17

Danzy83

17-Jul-11 10:17

Hi experts, I am reading a source file written in C and there is a declaration syntax which is not familiar to me. The source file is from libmad mp3 decoder. When the file in which the declaration is made has a file extension of .c, the c++ compiler is able to compile successfully. I have changed the source file extension to .cpp but the compiler reports an error. When I looked at the line from where the error was reported, I saw an array declaration which I do not understand very well. This is how the array has been declared.

unsigned char (*main_data)[MAD_BUFFER_MDLEN];

The declaration has been made in a structure called mad_stream. I am not certain about the pointer (*main_data). The following assignment generates an error:

stream->main_data = malloc(MAD_BUFFER_MDLEN);

and Microsoft Visual Studio 2005 reports the following error:

.\mad\layer3.cpp(2531) : error C2440: '=' : cannot convert from 'void *' to 'unsigned char (*)[2567]'<br />

Could someone please explain to me what is happening? What should I do?. Thanks.

Richard Andrew x6417-Jul-11 10:47

Re: array declaration [modified]

17-Jul-11 10:47

I think this is an array of unsigned char pointers.

unsigned char (*main_data)[MAD_BUFFER_MDLEN];  is somewhat equivalent to:

unsigned char **main_data;

The difference is that in the first declaration above, the entire array is created on the stack by the compiler.

You don't need to allocate this array with malloc since it's already on the stack.

The difficult we do right away...
...the impossible takes slightly longer.

Danzy8317-Jul-11 11:56

Danzy83

17-Jul-11 11:56

Right Richie, but do you have any idea how I should allocate the memory in C++ with the new operator for it to work? I still can't figure it out.

For instance, I was playing with this syntax in both C and C++. As an example, the following code compiled successfully when the file extension was .c:

#include <stdio.h>


int main(void)
{
    char (*ptr)[40];

    ptr = malloc(40);

    // some code...
    
    free(ptr);

    return 0;

}

However, by just changing the source file to .cpp, the code doesn't compile. Anyway of accomplishing this in C++?

modified on Sunday, July 17, 2011 7:14 PM

Richard Andrew x6417-Jul-11 13:45

17-Jul-11 13:45

~~Can you say exactly what error it gives when you say it doesn't compile in C++?~~

I know why it won't compile in C++, it's because C++ has stricter type checking.

You need to cast the output of the malloc call thus:

*ptr = (char*)malloc( sizeof(char*) * 40 );

The difficult we do right away...
...the impossible takes slightly longer.

Richard MacCutchan17-Jul-11 22:59

Richard MacCutchan

17-Jul-11 22:59

Richard Andrew x64 wrote:
I think this is an array of unsigned char pointers.

Sorry Richard, you are incorrect. This (awful) syntax needs to be read from inside the parenthesis and then right to left so that:
(*main_data) is a pointer, to [MAD_BUFFER_MDLEN] an array this length of unsigned chars.

The best things in life are not things.

«_Superman_»17-Jul-11 15:45

«_Superman_»

17-Jul-11 15:45

char (*p)[10]; is declaring a pointer to a fixed size array and is different from char *p[10]; which simply means an array of 10 pointers.
You allocate memory using p = new char[2][10]; and deallocate using delete [] p;

«_Superman_»
I love work. It gives me something to do between weekends.

Microsoft MVP (Visual C++)

Polymorphism in C

Richard Andrew x6417-Jul-11 16:14

17-Jul-11 16:14

Superman, thanks for stepping in.

What is the difference between a "fixed size array" and an "array of 10 pointers?"

The difficult we do right away...
...the impossible takes slightly longer.

«_Superman_»17-Jul-11 16:33

«_Superman_»

17-Jul-11 16:33

Take a look here - http://stackoverflow.com/questions/1810083/c-pointers-pointing-to-an-array-of-fixed-size[^]
All the secure C++ runtime functions like strcpy_s use this technique.

«_Superman_»
I love work. It gives me something to do between weekends.

Microsoft MVP (Visual C++)

Polymorphism in C

Richard Andrew x6417-Jul-11 17:32

17-Jul-11 17:32

Excellent. I just learned something very useful.

The difficult we do right away...
...the impossible takes slightly longer.

Richard MacCutchan17-Jul-11 23:08

Richard MacCutchan

17-Jul-11 23:08

I thought I understood this but I am now confused as to the memory allocation. Why new char[2][10] and not just new char[10]? Isn't p just an array of characters?

The best things in life are not things.

«_Superman_»18-Jul-11 9:10

«_Superman_»

18-Jul-11 9:10

Take a look at the following examples.

Say I have a function as below -

void fun(char (*p)[10])
{
    cout << *p << endl;    // Will output Hello
}

Now you will be able to call it as -

char name[10];
strcpy_c(name, "Hello");
fun(&name);

But you will get a compile error if you try something like -

char name[11];    // Wrong size
strcpy_c(name, "Hello");
fun(&name);

You could have a slightly different version using references -

void fun(char (&r)[10])
{
    cout << r << endl;    // Will output Hello
}

char name[10];
strcpy_c(name, "Hello");
fun(name);

char name2[11];    //Wrong size
strcpy_c(name2, "Hello");
fun(name2);    // Compile time error

So even though the code calling the function looks exactly like it does when using a function accepting a simple character pointer, it is a safe function.
This is exactly how the new safe string functions are implemented.
The advantage here is that you do not need to pass in a second size parameter to the function and the check for the size is done by the compiler at compile time.

But when you allocate memory using new, then it becomes something like -

char (*p)[10] = new char[5][10];

You can now pass this on to a function, but you would need another level of indirection -

void fun(char (**p)[10]){}
fun(&p);

void fun(char (*&p)[10]){}
fun(p);

«_Superman_»
I love work. It gives me something to do between weekends.

Microsoft MVP (Visual C++)

Polymorphism in C