BuildCommDCB

The BuildCommDCB function fills a specified DCB structure with values specified in a device-control string. The device-control string uses the syntax of the mode command.

BOOL BuildCommDCB(
  LPCTSTR lpDef,  // pointer to device-control string
  LPDCB lpDCB     // pointer to device-control block
);
 

Parameters

lpDef

Pointer to a null-terminated string that specifies device-control information. The string must have the same form as the mode command's command-line arguments. For example, the following string specifies a baud rate of 1200, no parity, 8 data bits, and 1 stop bit:

baud=1200 parity=N data=8 stop=1 
 

The device name is ignored if it is included in the string, but it must specify a valid device, as follows:

COM1: baud=1200 parity=N data=8 stop=1 

For further information on mode command syntax, refer to the end-user documentation for your operating system.

lpDCB

Pointer to a DCB structure to be filled in.

Return Values

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

The BuildCommDCB function adjusts only those members of the DCB structure that are specifically affected by the lpDef parameter, with the following exceptions:

• If the specified baud rate is 110, the function sets the stop bits to 2 to remain compatible with the system's mode command.
• By default, BuildCommDCB disables XON/XOFF and hardware flow control. To enable flow control, you must explicitly set the appropriate members of the DCB structure.

The BuildCommDCB function only fills in the members of the DCB structure. To apply these settings to a serial port, use the SetCommState function.

There are older and newer forms of the mode command syntax. The BuildCommDCB function supports both forms. However, you cannot mix the two forms together.

The newer form of the mode command syntax lets you explicitly set the values of the flow control members of the DCB structure. If you use an older form of the mode syntax, the BuildCommDCB function sets the flow control members of the DCB structure, as follows:

• For a string such as 96,n,8,1 or any other older-form mode string that doesn't end with an x or a p:

  fInX, fOutX,fOutXDsrFlow,and fOutXCtsFlow are all set to FALSE

  fDtrControl is set to DTR_CONTROL_ENABLE

  fRtsControl is set to RTS_CONTROL_ENABLE

• For a string such as 96,n,8,1,x or any other older-form mode string that finishes with an x:

  fInX, fOutX are both set to TRUE

  fOutXDsrFlow,fOutXCtsFlow are both set to FALSE.

  fDtrControl is set to DTR_CONTROL_ENABLE

  fRtsControl is set to RTS_CONTROL_ENABLE

• For a string such as 96,n,8,1,p or any other older-form mode string that finishes with a p:

  fInX, fOutX are both set to FALSE

  fOutXDsrFlow,fOutXCtsFlow are both set to TRUE.

  fDtrControl is set to DTR_CONTROL_HANDSHAKE

  fRtsControl is set to RTS_CONTROL_HANDSHAKE

QuickInfo

  Windows NT: Requires version 3.1 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Unsupported.
  Header: Declared in winbase.h.
  Import Library: Use kernel32.lib.
  Unicode: Implemented as Unicode and ANSI versions on Windows NT.

See Also

Communications Overview, Communication Functions, DCB, SetCommState