Function Declaration

• Description
• Syntax
• Operation

• Example
• Related
• History & Bugs

Function Constructs are a group of statements that specifies the beginning and end of section of code that forms the body of a function.

The following shows the formats of the Function Construct syntax.

Visual Basic & BASIC	C & Java
Function <funname>(<arglist>) As <type> <statements> [Exit Function] [<funname>=<returnvalue>] End Function	Function <type> <funname>(<arglist>) { <statements> return [<returnvalue>]; } BUG: return (); does not work in 5.0.1 compiler. Use the Basic syntax <funname> = <returnvalue>; instead

The following table lists the elements of the Function Constructs syntax.

Element		Description
Basic	C & Java
Function	Function	Function Construct beginning keyword. C and Java still need the Function heading to denote a function returning a value.
<funname>	<funname>	Name of the function. Follows standard naming conventions.
<arglist>	<arglist>	A list of Variables, and their names, that are used for passing values to the Function.  The format of the argument list is shown below. NOTE: This element is only available in ooPIC Compiler Version 3.0 and greater.
<type>	<type>	The type of value to pass back to the calling expression. May be one of the following; Byte and Word. Earlier compilers used objects for return values and argument lists, current compilers expect variables, not objects.
<statements>	<statements>	The statements that are executed.
Exit Function		Optional Function Construct termination keyword. Can occur any number of times within the <statements>
	return	Function Construct keyword that specifies the value to return
<returnvalue>	<returnvalue>	The value that this function returns.
End Function		Function Construct ending keyword.

The following shows the format of the <arglist> element.

([<id1> As <type1>[, <idX> As <typeX>[,...]]])

([<type1> <id1>[, <typeX> <idX>[,...]]][void])

The following table lists the elements of the <arglist> format.

When a function is called during the program's execution, the program flow's current position is saved on the Program-Stack and the program flow will then branch to the function specified by the <funname> element. After branching to the function, the program flow executes the statements within the <statements> element until either the end of the Function Construct or the optional termination keyword is encountered, at which time the original program flow position is retrieved off of the Program-Stack and the program flow is returned to its original position with the value specified by <returnvalue>.

The following rules apply to functions.

• A function may only be called from within an expression.

• A function always returns a value to the expression from which it was called.

You cannot define either procedures or functions inside another procedure or function.

Caution: Functions can be recursive; that is, they can call themselves. This can lead to stack overflow and must be used carefully.

Dim SW As New oDIO1
Dim A1 As New oA2D
Dim A2 As New oA2D
Dim P As New oDIO8

Sub Main()
  Call SetUp
  Do
    P = GetMyVal
  Loop
End Sub

Function GetMyVal() As Byte
  If SW.Value = cvPressed Then
    GetMyVal = A1.Value
  Else
    GetMyVal = A2.Value
  End If
End Function

Sub SetUp()
  SW.IOLine = 31
  SW.Direction = cvInput
  A1.IOLine = 1
  A1.Operate = cvTrue
  A2.IOLine = 2
  A2.Operate = cvTrue
  P.IOGroup = 1
  P.Direction = cvOutput
End Sub

oDIO1 SW = New oDIO1;
oA2D A1 = New oA2D;
oA2D A2 = New oA2D;
oDIO8 P = New oDIO8;

Sub Void Main(Void)
{
  SetUp;
  Do
  {
    P = GetMyVal;
  } While (1 == 1);
}

Function Byte GetMyVal(Void)
{
  If (SW.Value == cvPressed)
  {
    Return A1.Value;
  }
  Else
  {
    Return A2.Value;
  }
}

Sub Void SetUp(Void)
{
  SW.IOLine = 31;
  SW.Direction = cvInput;
  A1.IOLine = 1;
  A1.Operate = cvTrue;
  A2.IOLine = 2;
  A2.Operate = cvTrue;
  P.IOGroup = 1;
  P.Direction = cvOutput;
}

In the following example, a Function Construct is shown that takes two values as arguments, and then passes a Byte when finished.

Function GetMyVal(V1 As Byte, V2 as Word) As Byte

Bugs: No known bugs.