ucArg

ucArgStr

See Also: ucDefineFunction, ucDefineOperator, ucArgCount, ucArgHandle, ucReturn

Retrieves the argument(s) or operand(s) of a callback routine.

ucArg(ExpressionHandle, ArgIndex)

- or -

ucArgStr(ExpressionHandle, ArgIndex)

Parameters

ExpressionHandle

All Native callback routines receive one argument, which is ExpressionHandle.� This handle is required as the first argument of ucArg().

ArgIndex

This represents the index of the argument you want.� If a callback routine definition has three parameters, and Expr is the expression handle, then ucArg(Expr, 1) retrieves the first argument, ucArg(Expr, 2) the second, and ucArg(Expr, 3) the third.� For an infix operator, ucArg(Expr, 1) is the left operand, and ucArg(Expr, 2) is the right operand.� For a unary operator, ucArg(Expr, 1) is the operand.

Remarks

• ucArg() retrieves numeric arguments, while ucArgStr() retrieves string arguments.

� Depending on the compiler, ucArg is mapped to double precision or extended precision.

.Example 1:� Using ucArg with a function definition

The following routine defines a function named Add, which returns the result of adding its two arguments.� So Add(5, 4) would return 9.� For more details on defining a function, see ucDefineFunction.

Visual Basic

' The line below can go in Form_Load()

ucDefineFunction "Native: Add(a, b)", AddressOf MyAdd

' The line below goes in a separate module

Sub MyAdd(ByVal Expr As Long)

�� ucReturn Expr, ucArg(Expr, 1) + ucArg(Expr, 2)

End Sub

Examples for other compilers

Example 2:� Using ucArg with an operator definition

The following routine defines an operator named Plus, which returns the result of adding its two operands.� So 5 Plus 4 would return 9.� Note that the MyAdd callback is identical to the one in Example 1.� The only code that is different is the first line (ucDefineOperator ...).� The number 20 that comes after the word Native is the precedence level.� For more details on defining an operator, see ucDefineOperator.

Visual Basic

' The line below can go in Form_Load()

ucDefineOperator "Native: 20 {a} Plus {b}", AddressOf MyAdd

' The line below goes in a separate module

Sub MyAdd(ByVal Expr As Long)

�� ucReturn Expr, ucArg(Expr, 1) + ucArg(Expr, 2)

End Sub

Example 3:� Using ucArgStr for a string argument

This example demonstrates the use of ucArgStr.� Myleft is a function that returns the left-most characters of a string, which is supplied as the first argument.� The second argument determines the number of characters to return.� It is based on VB's Left$() function.� For instance MyLeft("Hello World", 2) would return "He".

Visual Basic

' The line below can go in Form_Load()

ucDefineFunction "Native: MyLeft(Text As String, Count) As String", AddressOf MyLeft

' The line below goes in a separate module

Sub MyLeft(ByVal Expr As Long)

��� ucReturnStr Expr, Left$(ucArgStr(Expr, 1), ucArg(Expr, 2))

End Sub

Additional examples can be found in the help topics for ucDefineFunction, and ucDefineOperator.

New or enhanced in version 3.0

� Nothing related to this topic.

� See What�s New.

Note: ucParam and ucParamStr were renamed ucArg and ucArgStr in version 3.0.� However, ucParam and ucParamStr are preserved for backward compatibility.

New or enhanced in version 2.96

• The use of ucParam was discouraged in version 2.9.� ucParam was optimized in 2.96 for speed and is now recommended for use with native callbacks.� You should now use ucParam instead of ucParamDbl or ucParamExt.