Action

Declares a user function.

 

 

Syntax

DECLARE FUNCTION TEST[( [BYREF/BYVAL] var as type)] As type

 

 

Remarks

 

When BYREF or BYVAL is not provided, the parameter will be passed by reference.

Use BYREF to pass a variable by reference with its address.

Use BYVAL to pass a copy of the variable.

 

See the CALL statement for more details.

 

 

You must declare each function before writing the function or calling the function. And the declaration must match the function.

Bits are global and can not be passed to functions or subs.

 

When you want to pass a string, you pass it with it's name : string. So the size is not important. For example :

Declare function Test(s as string, byval z as string) as byte

 

When you set the function result, you need to take care that no other code is executed after this.

So a good way to set the result would be this :

 

Function Myfunc(b as byte) as Byte

 local bDummy as byte

 'some code here

 Myfunc=3 ' assign result

 ' no other code is executed

End Function

 

Also good would be:

 

Function Myfunc(b as byte) as Byte

 local bDummy as byte

 'some code here

 Myfunc=1 ' assign default result

 Print "this is a test " ; b

 Myfunc=4 ' now again the result is the last code

 ' no other code is executed

End Function

 

If you execute other code after you assigned the function result, registers will be trashed. This is no problem if you assigned the function result to a variable. But when you use a function without assigning it to a variable, some temporarily registers are used which might be trashed.

 

 

Thus this special attention is only needed when you use the function like :

If Myfunc()=3 then  'myfunc is not assigned to a variable but the result is needed for the test

 

When you use :

myvar=Myfunc()

Then you will not trash the registers. So in such a case there is no problem to run code after the function assignment.

 

To keep it safe, assign the result just before you exit the function.

 

 

See also

CALL, SUB

 

 

Example

'-----------------------------------------------------------------------------------------

'name                     : function.bas

'copyright                : (c) 1995-2005, MCS Electronics

'purpose                  : demonstration of user function

'micro                    : Mega48

'suited for demo          : yes

'commercial addon needed  : no

'-----------------------------------------------------------------------------------------

 

$regfile = "m48def.dat"                                   ' specify the used micro

$crystal = 4000000                                         ' used crystal frequency

$baud = 19200                                               ' use baud rate

$hwstack = 32                                               ' default use 32 for the hardware stack

$swstack = 10                                               ' default use 10 for the SW stack

$framesize = 40                                             ' default use 40 for the frame space

 

'A user function must be declare before it can be used.

'A function must return a type

Declare Function Myfunction(byval I As Integer , S As String) As Integer

'The byval paramter will pass the parameter by value so the original value

'will not be changed by the function

 

Dim K As Integer

Dim Z As String * 10

Dim T As Integer

'assign the values

K = 5

Z = "123"

 

T = Myfunction(k , Z)

Print T

End

 

 

Function Myfunction(byval I As Integer , S As String) As Integer

'you can use local variables in subs and functions

Local P As Integer

P = I

'because I is passed by value, altering will not change the original

'variable named k

I = 10

 

P = Val(s) + I

 

'finally assign result

'Note that the same data type must be used !

'So when declared as an Integer function, the result can only be

'assigned with an Integer in this case.

Myfunction = P

End Function