Program Entry Point

All ViviFire programs must contain one module that starts with Program and a name. This module is where your program starts to run.

The name of the program can be the same as one procedure. When you write = before the name, that procedure becomes where the program starts to run. But, if = is not given, control starts at the top of the module.

A procedure lets you easily get arguments from the command line, and/or return an error code to the operating system. But if these are not necessary in your program, you can select not to use a procedure. There are alternatives you can use. For example, Exit Program can return an error code.

Declaration of the procedure

There are four different mixtures of parameters and return types. It can have one parameter or none, and it can return a value or not.

The easiest procedure is one that does not have parameters and does not return a value.

Program = NotMuch

Sub NotMuch
    MessageBox "Start of program"
    MessageBox "End of program"
End Sub

The procedure can return a value of the type Int32. The operating system uses this value as the error code for your program. Other programs can read this value.

Program = ErrorOnly

Sub ErrorOnly As Int32
    MessageBox "Start of program"
    ErrorOnly = %EXIT_SUCCESS
    MessageBox "End of program with error code " &
        ErrorOnly & "."
End Sub

The procedure can also have one parameter that is an array of String. Each item in the array is one of the command-line arguments given to run your program. You can select what to do with different arguments.

Program = ArgsAndError

Sub ArgsAndError(args() As String) As Int32
    MessageBox "Start of program"
    For Each arg In args
    Begin
        MessageBox arg & " arg"
    When DONE
        ArgsAndError = %EXIT_SUCCESS
    When NONE
        ArgsAndError = %EXIT_FAILURE
        MessageBox "No args!"
    End For
    MessageBox "End of program with error code " &
        ArgsAndError & "."
End Sub

The procedure can also examine the given arguments but not return an error code, as follows.

Program = ArgsOnly

Sub ArgsOnly(args() As String)
    MessageBox "Start of program"
    For Each arg In args
    Begin
        MessageBox arg & " arg"
    When NONE
        MessageBox "No args!"
    End For
    MessageBox "End of program"
End Sub

Program Entry Point

Declaration of the procedure

See also