The PI API provides a common programmer interface to PI System information.

The API is two files: PIAPI32.DLL & PILOG32.DLL which are the foundation of PI networking and data functionality
PIAPI32.dll – contains all of the “C” language functions necessary for any of the PI clients (including PI ProcessBook & PI DataLink) or any of PI’s high speed interfaces to interact with PI: reading and writing data, buffering system, informational functions, etc.
PILOG32.dll – contains all of the “C” language functions necessary to connect to PI servers, logon with security, and create and interpret data packets.

To Declare a Function
To declare a function in VB, you must use the Declare statement
Declare param1 param2 param3 param4 param5
param1: Function or Sub
param2: Name of the function
param3: Lib
param4: File name and library directory of PI API
param5: List of arguments

Example:

Declare Function piar_putvalue Lib "piapi32.dll" (ByVal pt&, ByVal rval!, _ 

                           ByVal istat&, ByVal Timedate&, ByVal wait&) As Long

Note: The file \PIPC\INCLUDE\PIAPI32.BAS contains all PI API functions, procedures and PI variable types definitions.

API Return of Functions
Most functions return a number to indicate if the function ran correctly

1. < 0 Parameter error in the function or unavailable information in PI
2. = 0 Success
3. > 0 System error (Computer or communication error)

Error Handling

To prevent an application from crashing due to an error occurring, follow these steps:

1. Trap errors
2. Display error number and description
3. Resume execution of the application after quitting the faulty procedure

To trap an error

On Error GoTo ErrH_Procedure_Name

To display the trapped error

MsgBox Err.Number & " - " & Err.Description

Resume Exit_Procedure_Name

To exit the procedure or take corrective action

Exit_Procedure_Name:

    Exit Sub

Example:

Private Sub Sample()

    On Error GoTo ErrH_Sample

    'Code

    '.....

    '.....

    'End code

    Exit_Sample:

        Exit Sub

    ErrH_Sample:

        MsgBox Err.Number & " - " & Err.Description

        Resume Exit_Sample

End Sub