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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.

John

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md041797

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langlois

ASKER

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",
GENERIC_READ | GENERIC_WRITE,
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
);

if (hCom == INVALID_HANDLE_VALUE)
      Label1->Caption = "CreateFile(): Failed";
else
      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";
else
      Label2->Caption = "SetupComm(): Passed";

///////////
fSuccess = GetCommState(hCom, &dcb);

if (!fSuccess)
      Label3->Caption = "GetCommState(): Failed";
else
      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";
else
      Label4->Caption = "BuildCommDCB(): Passed";

///////////
fSuccess = SetCommState(hCom, &dcb);

if (!fSuccess)
      Label5->Caption = "SetCommState(): Failed";
else
      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";
else
      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";
else
      Label7->Caption = "ReadFile(): Passed";

buffer[dwNumberOfBytesRead]='\0';
Label8->Caption = buffer;

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

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

md041797

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.