Technical Reference > CtAPI Functions > Function Reference > ctTagRead

ctTagRead

Reads the value, quality and timestamp, not only a value. The data will be returned in string format and scaled using the CitectSCADA scales.

The function will request the given tag from the CitectSCADA I/O Server. If the tag is in the I/O Servers device cache the data will be returned from the cache. If the tag is not in the device cache then the tag will be read from the I/O Device. The time taken to complete this function will be dependent on the performance of the I/O Device. The calling thread is blocked until the read is completed.

Syntax

ctTagRead(hCTAPI, sTag, sValue, dwLength)

hCTAPI

Type: Handle
Input/output: Input
Description: The handle to the CTAPI as returned from ctOpen().

sTag

Type: LPCSTR
Input/output: Input
Description: The tag name or tag name and element name, separated by a dot. If the element name is not specified, it will be resolved at runtime as for an unqualified tag reference. You may use the array syntax [] to select an element of an array.

sValue

Type: LPCSTR
Input/output: Output
Description: The buffer to store the read data. The data is returned in string format.

dwLength

Type: Dword
Input/output: Input
Description: The length of the read buffer. If the data is bigger than the dwLength, the function will not succeed.

Return Value

TRUE if successful, otherwise FALSE. Use GetLastError() to get extended error information.

Related Functions

ctOpen, ctTagWrite, ctTagWriteEx

Example

HANDLE   hCTAPI = ctOpen(NULL, NULL, NULL, 0);

		 
char	sProcessValue[20];
char	sProcessValueField[20];
char	sProcessValueControlMode[20];
char	sProcessValueStatus[20];
ctTagRead(hCTAPI,"PV123", sProcessValue, sizeof(sProcessValue));
ctTagRead(hCTAPI,"PV123.Field", sProcessValueField, sizeof(sProcessValueField));
ctTagRead(hCTAPI,"PV123.Field.V", sProcessValueField, sizeof(sProcessValueField));
ctTagRead(hCTAPI,"PV123.ControlMode",sProcessValueControlMode, sizeof(sProcessValueControlMode));
ctTagRead(hCTAPI, "PV123.Status", sProcessValueStatus, sizeof(sProcessValueStatus));