Why, when passing an array element to a function through a ParamArray, does a varpointer arrive in the function?

user_10312272 0
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I have noticed an oddity in VBA when using ParamArray and passing array elements through it. In some cases it is not the value of the array element that arrives in a function, but the var pointer. (Excel 2016, 32-bit).

After some plodding I found that the definition of the function as a variant array - in combination with a parameter list combined with a ParamArray - seems to be where the unexpected behaviour originates, but I can't see any feasible reasons why this would be so.

The behaviour reverts to normal when:
1) the variable r is removed in the function declarations
2) b is declared with Dim b()
3) the function returns a Variant, rather than a Variant()

I appreciate that it's a rather esoteric question, and it appears to be controllable for in various ways, but is there an explanation out there that elucidates this behaviour?

Sub Variantarraybug()
   Dim b: b = [{1, 2, 3}]

   Debug.Print farray1(2, b(1))(0)
   Debug.Print Application.WorksheetFunction.Sum(farray1(2, b(1)))
   Debug.Print Join(farray1(2, b(1)), " ")

   Debug.Print farray2(2, b(1))(0)
   Debug.Print Application.WorksheetFunction.Sum(farray2(2, b(1)))
   Debug.Print Join(farray2(2, b(1)), " ")
   Debug.Print  VarPtr(b(1)), VarPtr(b(2))
End Sub

Function farray1(r, ParamArray plop()) As Variant
   farray1 = Array(plop(0), 3)
End Function
Function farray2(r, ParamArray plop()) As Variant()
   farray2 = Array(plop(0), 5)
End Function

Result in the debug window:

 1  
 4  
1 3  
 1  
 6  
358808368 5  
 358808368     358808384

Note 1: My understanding is that the VarPtr function returns the memory location of the start address of the memory required by that variable. Here it is used only to demonstrate that the unexpected number (358808368) that was seen by the farray2 function, is in fact the address of that element.

Note 2: This happens independent of how you generate the array (e.g. b=array(1,2,3), b=[1,2,3], etc.) and how b is declared (b, b(1 to 3), etc.). However, if you declare b with Dim b(), the unexpected behaviour disappears. (You can't print VarPtr(b) in that case, as VarPtr cannot accept array variables.)

vba excel function arrays
2 Answers

I think that this bug appear due to the array "declaration". In this point, I think that Microsoft states that one clearly:

Arrays

You can declare a variable to hold an array, which can hold multiple values. To specify that a variable holds an array, follow its variablename immediately with parentheses.

On here

user_117671400

I think, it is a carelessness in "C". You get such an error with

#include <stdio.h>

int main(int argc, char **argv)
{
   int *X;
   int i;
   
   i = 7;
   X = &i;
   
   printf("%d\n", X);
   printf("%d\n", *X);
   
   return(0);
}

Elaboration:

"C" is a kind of abstract assembler. You have to understand the concept of accessing memory through addresses (or pointers). With

int i;

you declare a variable, that holds an integer (the number of bits of this integer depends on the compiler). With

i = 7;

you define the value of this variable in memory (here 7). With

int *X;

you declare a variable, which holds a value of a pointer (the number of bits of a pointer depends on the compiler; often the number of bits of an integer and a pointer are equal) to a location, which contains an integer. With

X = &i;

you define the value of the pointer X as the address of the variable i. With

*X

you have access to the (integer) value in memory of the location, where X points to. With

printf("%d\n", X);

you print the value of the pointer X (interpreted as integer). With

printf("%d\n", *X);

you print the (integer) value of the memory, where X points to.

I believe, someone forgot a "*".

user_159642410
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