ByVal param As datatype

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

ByVal in a parameter list of a declare statement causes a copy of the variable to be passed to the procedure (for example, a sub or function) by its value.

This means that if the value of the variable x is passed, then the original variable x will not be modified in any way; however, if the variable were passed ByRef, the value of the original variable x could be modified by the called function.

Opposite of ByRef.

The ByVal keyword is also used in the context of Byref Parameters and Function Results, where it can be used to explicitly override the by-reference semantics in order to pass or assign a pointer as-is to a Byref parameter or function result. For reference:

• Manually passing pointers to by-reference parameters
  
• Manually returning pointers as-is from Byref functions
  
  

Sub MySub(ByVal value As Integer)
    value += 1
End Sub

Dim MyVar As Integer

MyVar = 1
Print "MyVar: "; MyVar 'output = 1
MySub MyVar
Print "MyVar: "; MyVar 'output = 1, because byval won't change the values passed into it globally.
Sleep
End

• In the -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.
  
• In -lang qb and -lang fblite dialects, ByRef is the default parameter passing convention.
  
  

• QB only used ByVal in declarations to non-Basic subroutines
  
  

• Passing Arguments to Procedures
  
• Declare
  
• ByRef