Technical Reference > CtAPI Functions > Function Reference > ctListAdd


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.


ctListAdd(hList, sTag)


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.

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, ctListAddEx


HANDLE  hList;
HANDLE  hTagOne;
HANDLE  hTagOneField;
HANDLE  hTagOneControlMode;
HANDLE  hTagOneStatus;
char	sProcessValue[20];
char	sProcessValueField[20];
char	sProcessValueControlMode[20];
char	sProcessValueStatus[20];
hCTAPI				= ctOpen(NULL, NULL, NULL, 0);
hList				 = ctListNew(hCTAPI, 0);
hTagOne						 = ctListAdd(hList, "TagOne");
hTagOneField			= ctListAdd(hList, "TagOne.Field");
hTagOneControlMode	= ctListAdd(hList, "TagOne.ControlMode");
hTagOneStatus		 = ctListAdd(hList, "TagOne.Status");
ctListRead(hList, NULL);
ctListData(hTagOne, sProcessValue, sizeof(sProcessValue), 0);
ctListData(hTagOneField, sProcessValueField, sizeof(sProcessValueField) , 0);
ctListData(hTagOneControlMode, sProcessValueControlMode, sizeof(sProcessValueControlMode) , 0);
ctListData(hTagOneStatus, sProcessValueStatus, sizeof(sProcessValueStatus) , 0);