Technical Reference > CtAPI Functions > Function Reference > ctListAddEx


Performs the same as ctListAdd, but with 2 additional new arguments. Adds a tag, or tag element, to the list. Once the tag has been added to the list, it may be read using ctListRead() and written to using ctListWrite(). If a read is already pending, the tag will not be read until the next time ctListRead() is called. ctListWrite() may be called immediately after the ctListAdd() function has completed.

If ctListAdd is called instead of ctListAddEx, The poll period of the subscription for the tag defaults to 500 milliseconds, and the bRaw flag defaults to the engineering value of FALSE.


ctListAddEx(hList, sTag, bRaw, nPollPeriodMS, dDeadband)


Input/output: Input
Description: The handle to the list, as returned from ctListNew().


Input/output: Input
Description: The tag or tag name and element name, separated by a dot to be added to the list. If the element name is not specified, it will be resolved at runtime as for an unqualified tag reference.


Type: BOOL
Input/output: Input
Description: Specifies whether to subscribe to the given tag in the list using raw mode if TRUE or engineering mode if FALSE.


Input/output: Input
Description: Dictates the poll period used in the subscription made for the tag (in milliseconds).


Input/output: Input
Description: Percentage of the variable tag's engineering range that a tag needs to change by in order for an update to be sent through the system. A value of -1.0 indicates that the default deadband specified by the tag definition is to be used.

Return Value

If the function succeeds, the return value specifies a handle. If the function does not succeed, the return value is NULL. To get extended error information, call GetLastError()

If a tag not currently defined in your system is specified using this function then the return value will specify a valid handle. Calling ctListRead will allow identification of the true state of the tag. Passing an empty tag to this function will result in the function exiting immediately and returning NULL.

Related Functions

ctOpen, ctListNew, ctListFree, ctListRead, ctListWrite, ctListData, ctListItem


See ctListNew