OpenInput Method

Processes the specified from-entity and performs any necessary initialization.

C++ Syntax

HRESULT STDMETHODCALLTYPE OpenInput(IN BSTR bszFromEntity);

Script Syntax

OpenInput(bszFromEntity);

Parameters

bszFromEntity

The from-entity specified in the FROM clause of the currently executing query, or an empty string if Log Parser is executed in Help Mode to display the quick-reference help on the custom input format.

Return Value

Remarks

• The OpenInput method is the first method called by Log Parser after the custom input format COM object has been instantiated. An implementation of this method would usually perform any necessary object initialization, prepare the from-entity for input record retrieval (e.g. opening an input file), and eventually pre-process the input to gather the input record fields meta-information that will be returned by the GetFieldCount, GetFieldName, and GetFieldType methods.
• Users can execute the Log Parser command-line executable in Help Mode to display a quick-reference help on a custom input format. The quick-reference help displays the input record field names and types, which are retrieved through calls to the GetFieldCount, GetFieldName, and GetFieldType methods.
  If the user-supplied help mode command does not include a from-entity, the bszFromEntity argument wil be an empty string. In these cases, a custom input format COM object can behave in two ways:
  • If the input record fields do not depend on the from-entity specified in the query (i.e. if the input record structure is fixed), then the custom input format COM object should accept the empty from-entity without returning an error, allowing Log Parser to subsequently call the GetFieldCount, GetFieldName, and GetFieldType methods to retrieve the input record structure;
  • If the input record fields depend on the from-entity specified in the query (i.e. if the input record structure is extracted from the input data), then the custom input format COM object should reject the empty from-entity returning an error, which will in turn cause the help command to display a warning message to the user in place of the input record structure.

Examples

C++ example:

HRESULT CProcessesInputContext::OpenInput( IN BSTR bszFromEntity )
{
        // Initialize object
        ...

        // This input format does not require a from-entity, so
        // we will just ignore the argument 

	return S_OK;
}

VBScript example:

Function OpenInput(strComputerName)

	Dim objWMIService
	Dim objQFEs
	Dim nLength
	
	' Default computer name is local machine
	If IsNull(strComputerName) Or Len(strComputerName) = 0 Then
		strComputerName = "."
	End If

	' Query for all the QFE's on the specified machine
	Set objWMIService = GetObject("winmgmts:" & "{impersonationLevel=impersonate}!\\" & strComputerName & "\root\cimv2")
	Set objQFEs = objWMIService.ExecQuery ("Select * from Win32_QuickFixEngineering")

	' Store in array
	m_objQFEArray = Array()
	For Each objQFE In objQFEs
		ReDim Preserve m_objQFEArray( UBound(m_objQFEArray) + 1 )
		Set m_objQFEArray( UBound(m_objQFEArray) ) = objQFE
	Next

	m_nIndex = LBound(m_objQFEArray)

End Function

See also:

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