Byref (Parameters)
 
Declaration specifier to explicitly pass a parameter by reference

Syntax

ByRef param As datatype

Usage

[ Declare ] { Sub | Function } proc_name ( ByRef param As datatype )

Description

Passes a variable by reference, that is its address, to a subroutine or function. When a variable is passed by reference, the contents of the variable can be changed by the target subroutine or function.

In -lang qb and -lang fblite dialects, ByRef is the default parameter passing convention, unless Option ByVal is in effect.

Opposite of ByVal.

Note: A constant or a literal expression can also be passed to such a procedure (which gets by reference), but they are obviously not modifiable from the procedure body. In that case, the compiler passes by reference a temporary variable initialized with the constant or the literal expression.

Warning: When passing by reference, it is recommended to pass an argument of the same type (or fully compatible, like a derived type for example) as that of the declared parameter. Although in some cases the compiler accepts to pass a different type, often the result is not the one expected.

Example

Dim MyVar As Integer

Sub ChangeVar(ByRef AVar As Integer)
    AVar = AVar + 1
End Sub

MyVar = 1
Print "MyVar: "; MyVar 'output = 1
ChangeVar MyVar
Print "MyVar: "; MyVar 'output = 2
Sleep
End


Dialect Differences

  • In -lang fb dialect, ByVal is the default parameter passing convention for all built-in types except String and user-defined Type which are passed ByRef by default. The ZString and WString built-in types are also passed ByRef by default, but passing ByVal is forbidden. Arrays are always passed ByRef and the use of the specifier ByRef or ByVal is forbidden.
  • In -lang qb and -lang fblite dialects, ByRef is the default parameter passing convention.

Differences from QB

  • New to FreeBASIC

See also