ByVal
Declaration specifier to explicitly pass a parameter by value
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.
Note: For string arguments, ByVal currently has a different meaning: instead of passing a copy of the string, it passes a ZString pointer to the string data, while ByRef passes a pointer to the FreeBASIC string descriptor. This behavior allows passing a ByVal String directly to C procedures. The string passed this way should not be changed by the Sub/Function, as the string descriptor would not be updated. The meaning of passing a String ByVal might change in the future; therefore, passing a String ByVal should be avoided. ZString is more suited for the purpose of passing zero-terminated strings to C functions.
Opposite of ByRef.
Syntax
Usage
Description
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.
Note: For string arguments, ByVal currently has a different meaning: instead of passing a copy of the string, it passes a ZString pointer to the string data, while ByRef passes a pointer to the FreeBASIC string descriptor. This behavior allows passing a ByVal String directly to C procedures. The string passed this way should not be changed by the Sub/Function, as the string descriptor would not be updated. The meaning of passing a String ByVal might change in the future; therefore, passing a String ByVal should be avoided. ZString is more suited for the purpose of passing zero-terminated strings to C functions.
Opposite of ByRef.
Example
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
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
Dialect Differences
Differences from QB
- QB only used ByVal in declarations to non-Basic subroutines
See also
