Re: <SNIP>You haven't set dcb.

francois delamotte <>
Mon, 23 Jan 2012 12:01:20 GMT
i am using the same code as cheng. Even with the dcb.DCBLENGTH=sizeof(DCB) the program returns error 87. Are there any other possible causes?

On Monday, April 14, 2008 11:01 AM Scott McPhillips [MVP] wrote:

"uvbaz" <> wrote in message

Error 87 usually means you have made a simple programming mistake with the
parameters. Can you show the relevant lines of the code? It is very hard
to guess what is wrong if you do not show some code.

Scott McPhillips [VC++ MVP]

On Wednesday, April 16, 2008 2:23 AM Check Abdoul wrote:

char *pcCommPort = "\\\\.\\COM1"

Check Abdoul

On Wednesday, April 16, 2008 3:32 AM Anthony Wieser wrote:


You have not set dcb.DCBlength = sizeof(dcb), so it will fail, as it does not
know what size the strucure is.

Anthony Wieser
Wieser Software Ltd

On Wednesday, April 16, 2008 9:40 PM uvbaz wrote:


i'm trying to set the serial port.(XP SP2, Visual Studio 2005). I use
the example code from MSDN "configuring a communications resource".

CreateFile pass through, however GetCommState return 0.With
GetLastError(), i get the error number 87, which means
"ERROR_INVALID_PARAMETER The parameter is incorrect. "
I'm sure the serial port works, because i can use another program to
read/write through it.


On Wednesday, April 16, 2008 9:40 PM uvbaz wrote:

On 14 Apr., 17:01, "Scott McPhillips [MVP]" <org-dot-mvps-at-scottmcp>

Sorry, i forgot to paste them.

int main(int argc, char *argv[])
   DCB dcb;
   HANDLE hCom;
   BOOL fSuccess;
   char *pcCommPort = "COM1";

   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

       // Handle the error.
       printf ("CreateFile failed with error %d.\n", GetLastError());
       return (1);

   // Build on the current configuration, and skip setting the size
   // of the input and output buffers with SetupComm.

   fSuccess = GetCommState(hCom, &dcb);

   if (!fSuccess)
      // Handle the error.
      printf ("GetCommState failed with error %d.\n", GetLastError());
      return (2);

   // Fill in DCB: 57,600 bps, 8 data bits, no parity, and 1 stop bit.

   dcb.BaudRate = CBR_57600; // set the baud rate
   dcb.ByteSize = 8; // data size, xmit, and rcv
   dcb.Parity = NOPARITY; // no parity bit
   dcb.StopBits = ONESTOPBIT; // one stop bit

   fSuccess = SetCommState(hCom, &dcb);

   if (!fSuccess)
      // Handle the error.
      printf ("SetCommState failed with error %d.\n", GetLastError());
      return (3);

   printf ("Serial port %s successfully reconfigured.\n", pcCommPort);
   return (0);

On Sunday, April 20, 2008 7:41 PM Joseph M. Newcomer wrote:

I presume there was some actual code that caused this error. How are we expected to offer
advice if you don't show the code that failed?

On Mon, 14 Apr 2008 05:59:56 -0700 (PDT), uvbaz <> wrote:

Joseph M. Newcomer [MVP]
MVP Tips:

On Sunday, April 20, 2008 7:47 PM Joseph M. Newcomer wrote:

See below...
On Tue, 15 Apr 2008 01:08:30 -0700 (PDT), uvbaz <> wrote:

int _tmain(int argc _TCHAR * argv[])
First, why are you using an obsolete data type like 'char'? Why are you declaring a
variable at all?

The correct code would at the very least be
    LPTSTR CommPort = _T("COM1");
but that is not really general; the correct name is actually
because the string you use is only good for COM1..COM9, and fails utterly with COM10.
Which is only one of about a dozen possible values you could use here; why single out
FILE_FLAG_OVERLAPPED as being the only flag of meaning?
Did you actually READ THE DOCUMENTATION about DCB? Error 87 is EXACTLY the correct
response; you failed to initialize the first element, the DCBlength field. This could be
done by writing
    DCB dcb = { sizeof(DCB) };
or by explicitly assigning the lenght. The error code is correct; you provided an invalid
Joseph M. Newcomer [MVP]
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