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Serial i/o using Borland C++ Builder

I'm trying to write a simple serial instrument controller using Builder.

There doesn't appear to be a specific object for the serial port. I need to select a port, set the parameters (speed, parity, etc.) and then read & write control records. I'll need to log and act on the read data continuously while the user accesses other menus too. Surely a common enough requirement? But since I'm new to Windows and Builder programming, I'd appreciate a fairly detailed answer...

Many thanks in advance.

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1 Solution
Use the CreateFile API to get r/w access to your port:

HANDLE port = CreateFile ("\\\\.\\COM1", GENERIC_READ |

Then use ReadFile / WriteFile to r/w.  The system buffers the io so you don't have to worry about multi-threading.

Use BuildCommDCB() to set the port (similar to MODE command).

Use SetupComm() to make the port sane.

If you need more help, just tell me where you are having problems.

langloisAuthor Commented:
Okay MD,

I've at least established communication which is encouraging. But I'm not exactly able to set up my instrument controller yet. When I do a ReadFile(), I get to hang and wait until the requested number of chars have arrived. Makes it kinda hard to handle variable length records which may not even arrive! So how do I read data _if_ it's there but return regardless? For the record, here's the relevant snip from my kludgy test code as it stands:

DCB            dcb;
HANDLE      hCom;
DWORD      dwNumberOfBytesWritten, dwNumberOfBytesRead;
BOOL      fSuccess;
char      buffer[1024];

hCom = CreateFile("\\\\.\\COM2",
    0,                                  // comm devices must be opened w/exclusive-access
    NULL,                               // no security attrs
    OPEN_EXISTING,                  // comm devices must use OPEN_EXISTING
    FILE_ATTRIBUTE_NORMAL,      // not overlapped I/O
    NULL                                // hTemplate must be NULL for comm devices

      Label1->Caption = "CreateFile(): Failed";
      Label1->Caption = "CreateFile(): Passed";

fSuccess = SetupComm(
    hCom,      // handle of communications device
    1024,      // size of input buffer
    1024      // size of output buffer

if (!fSuccess)
      Label2->Caption = "SetupComm(): Failed";
      Label2->Caption = "SetupComm(): Passed";

fSuccess = GetCommState(hCom, &dcb);

if (!fSuccess)
      Label3->Caption = "GetCommState(): Failed";
      Label3->Caption = "GetCommState(): Passed";

fSuccess = BuildCommDCB(
    "baud=9600 parity=N data=8 stop=1",      // pointer to device-control string
    &dcb                                                // pointer to device-control block
if (!fSuccess)
      Label4->Caption = "BuildCommDCB(): Failed";
      Label4->Caption = "BuildCommDCB(): Passed";

fSuccess = SetCommState(hCom, &dcb);

if (!fSuccess)
      Label5->Caption = "SetCommState(): Failed";
      Label5->Caption = "SetCommState(): Passed";

fSuccess = WriteFile(
    hCom,                                    // handle to file to write to
    "echo fred\r",                        // pointer to data to write to file
    10,                                          // number of bytes to write
    &dwNumberOfBytesWritten,      // pointer to number of bytes written
    NULL                                     // pointer to structure needed for overlapped I/O

if (!fSuccess)
      Label6->Caption = "WriteFile(): Failed";
      Label6->Caption = "WriteFile(): Passed";

fSuccess = ReadFile(
    hCom,                              // handle of file to read
    buffer,                              // address of buffer that receives data
    16,                                    // number of bytes to read
    &dwNumberOfBytesRead,      // address of number of bytes read
    NULL                               // address of structure for data

if (!fSuccess)
      Label7->Caption = "ReadFile(): Failed";
      Label7->Caption = "ReadFile(): Passed";

Label8->Caption = buffer;

CloseHandle(hCom);                         // handle to object to close

if (!fSuccess)
      Label9->Caption = "CloseHandle(): Failed";
      Label9->Caption = "CloseHandle(): Passed";

Use the overlapped feature.  This will read as many chars as have arrived, return immediately, and it will report the count.  You can then assemble your records in a queue and pull them out when they are complete.
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