VB COM, how to pass Safearrays really byref (avoid copy)

how to pass Safearrays really byref (avoid copy)

Author	Message
sabb #1 / 6	how to pass Safearrays really byref (avoid copy) hi, i've noticed that there is no way to pass arrays in Vb "really" byref i mean this: suppose class A has the method public sub getarray(byref p_Array() as double) i_array = p_array 'i_array is an instance variable exit sub if i call this method in this way: dim a1 as new A dim l_array() as double redim l_Array(1 to 1000000) as double for x = 1 to 100000 l_Array(x) = rnd next a1.getarray(l_array) i can see that the memory grows once when i redim in the caller code (as i expected) but i can see that the memory grows again in the line i_array = p_array in the getarray method and this is not what i want i would like to avoid the copy of data , in C++ you get this passing a pointer .. how to do it in VB ? i remember there are some undocumented functions in Vb about pointer could they help me ? TIA,sabba -- Enrico Sabbadin http://www.--.com/ MTS FAQ: http://www.--.com/
Mon, 01 Jul 2002 03:00:00 GMT

Mark Burn #2 / 6	how to pass Safearrays really byref (avoid copy) sabba, I'm far from the most expert here, but from what I have come to understand about arrays and array assignment statements in VB - the behavior you are experiencing is exactly what VB specifies should occur. The i_array = p_array statement is an assignment statement where you are assigning (copying/duplicating) the p_array array to a new (variant) array variable (variants are the only variable types allowed to be on the left of the "=" sign in an array assignment statement). If i read your intentions correctly, why do you even need the i_array variable? Why not just keep referencing the p_array variable throught the remainder of your function (& sub-function calls), which BTW does indeed seem to be being passed "byref" BTW (else how could it take part in the assignment statement and not eat RAM until the i_array=p_array line - a byval p_array call would have eaten memory at (just after it was executed) the a1.getarray(l-array) line, right?" Quote: > hi, i've noticed that there is no way to pass arrays in Vb "really" byref > i mean this: > suppose class A has the method > public sub getarray(byref p_Array() as double) > i_array = p_array 'i_array is an instance variable > exit sub > if i call this method in this way: > dim a1 as new A > dim l_array() as double > redim l_Array(1 to 1000000) as double > for x = 1 to 100000 > l_Array(x) = rnd > next > a1.getarray(l_array) > i can see that the memory grows once when i redim in the caller code (as i > expected) > but i can see that the memory grows again in the line i_array = p_array in > the getarray method and this is not what i want > i would like to avoid the copy of data , in C++ you get this passing a > pointer .. how to do it in VB ? > i remember there are some undocumented functions in Vb about pointer could > they help me ? > TIA,sabba > -- > Enrico Sabbadin > http://sabbadin.tripod.com > MTS FAQ: http://sabbadin.tripod.com/mts_faq.htm
Mon, 01 Jul 2002 03:00:00 GMT

Gene Pinsk #3 / 6	how to pass Safearrays really byref (avoid copy) There are ObjPtr, StrPtr and VarPtr functions within VBA.HiddenModule. I haven't used them extensively but you could try to play with them and see if it helps. Quote: > hi, i've noticed that there is no way to pass arrays in Vb "really" byref > i mean this: > suppose class A has the method > public sub getarray(byref p_Array() as double) > i_array = p_array 'i_array is an instance variable > exit sub > if i call this method in this way: > dim a1 as new A > dim l_array() as double > redim l_Array(1 to 1000000) as double > for x = 1 to 100000 > l_Array(x) = rnd > next > a1.getarray(l_array) > i can see that the memory grows once when i redim in the caller code (as i > expected) > but i can see that the memory grows again in the line i_array = p_array in > the getarray method and this is not what i want > i would like to avoid the copy of data , in C++ you get this passing a > pointer .. how to do it in VB ? > i remember there are some undocumented functions in Vb about pointer could > they help me ? > TIA,sabba > -- > Enrico Sabbadin > http://sabbadin.tripod.com > MTS FAQ: http://sabbadin.tripod.com/mts_faq.htm
Mon, 01 Jul 2002 03:00:00 GMT

Thomas Wac #4 / 6	how to pass Safearrays really byref (avoid copy) Try this code, it may work. Did not test it, but the way should be right. cu Thomas Public Declare Sub RtlMoveMemory Lib "kernel32" (lpDest As Any, lpSource As Any, ByVal lCount As Long) public sub getarray(byval lpArray as long) 'receive a pointer here dim i_array As Variant const SIZE_OF_STRUCT_VARIANT = 8 ' or is ist 16? ' copy the bytes lpArray points to, to the address where i_array resides in memory RTLMoveMemory i_array, ByVal lpArray, SIZE_OF_STRUCT_VARIANT i_array(32) = 3.1415 ' or whatever you wanna do :-) ' you must clear i_array manual, or vb will destroy your array on sub-exit, I think. RTLMoveMemory i_array, ByVal 0, SIZE_OF_STRUCT_VARIANT exit sub end sub .... .... a1.getarray(VarPtr(l_array)) 'pass a pointer here Msgbox I_array(32) Quote: > There are ObjPtr, StrPtr and VarPtr functions within VBA.HiddenModule. > I haven't used them extensively but you could try to play with them and see > if it helps. > > hi, i've noticed that there is no way to pass arrays in Vb "really" byref > > i mean this: > > suppose class A has the method > > public sub getarray(byref p_Array() as double) > > i_array = p_array 'i_array is an instance variable > > exit sub > > if i call this method in this way: > > dim a1 as new A > > dim l_array() as double > > redim l_Array(1 to 1000000) as double > > for x = 1 to 100000 > > l_Array(x) = rnd > > next > > a1.getarray(l_array) > > i can see that the memory grows once when i redim in the caller code (as i > > expected) > > but i can see that the memory grows again in the line i_array = p_array in > > the getarray method and this is not what i want > > i would like to avoid the copy of data , in C++ you get this passing a > > pointer .. how to do it in VB ? > > i remember there are some undocumented functions in Vb about pointer could > > they help me ? > > TIA,sabba > > -- > > Enrico Sabbadin > > http://sabbadin.tripod.com > > MTS FAQ: http://sabbadin.tripod.com/mts_faq.htm
Mon, 01 Jul 2002 03:00:00 GMT

SaBb #5 / 6	how to pass Safearrays really byref (avoid copy) thank thomas, i had come to the conclusion i had to use varptr, still i had no idea how to re-attach the pointer to an array in my method call i'll try the code you posted and let you know thank again -- Home Page: http://sabbadin.tripod.com MTS FAQ: http://sabbadin.tripod.com/mts_faq.htm Try this code, it may work. Did not test it, but the way should be right. cu Thomas Public Declare Sub RtlMoveMemory Lib "kernel32" (lpDest As Any, lpSource As Any, ByVal lCount As Long) public sub getarray(byval lpArray as long) 'receive a pointer here dim i_array As Variant const SIZE_OF_STRUCT_VARIANT = 8 ' or is ist 16? ' copy the bytes lpArray points to, to the address where i_array resides in memory RTLMoveMemory i_array, ByVal lpArray, SIZE_OF_STRUCT_VARIANT i_array(32) = 3.1415 ' or whatever you wanna do :-) ' you must clear i_array manual, or vb will destroy your array on sub-exit, I think. RTLMoveMemory i_array, ByVal 0, SIZE_OF_STRUCT_VARIANT exit sub end sub .... .... a1.getarray(VarPtr(l_array)) 'pass a pointer here Msgbox I_array(32) Quote: > There are ObjPtr, StrPtr and VarPtr functions within VBA.HiddenModule. > I haven't used them extensively but you could try to play with them and see > if it helps. > > hi, i've noticed that there is no way to pass arrays in Vb "really" byref > > i mean this: > > suppose class A has the method > > public sub getarray(byref p_Array() as double) > > i_array = p_array 'i_array is an instance variable > > exit sub > > if i call this method in this way: > > dim a1 as new A > > dim l_array() as double > > redim l_Array(1 to 1000000) as double > > for x = 1 to 100000 > > l_Array(x) = rnd > > next > > a1.getarray(l_array) > > i can see that the memory grows once when i redim in the caller code (as i > > expected) > > but i can see that the memory grows again in the line i_array = p_array in > > the getarray method and this is not what i want > > i would like to avoid the copy of data , in C++ you get this passing a > > pointer .. how to do it in VB ? > > i remember there are some undocumented functions in Vb about pointer could > > they help me ? > > TIA,sabba > > -- > > Enrico Sabbadin > > http://sabbadin.tripod.com > > MTS FAQ: http://sabbadin.tripod.com/mts_faq.htm
Fri, 05 Jul 2002 03:00:00 GMT

Andre #6 / 6	how to pass Safearrays really byref (avoid copy) Hi Sabba, I thought that in VB6 all arrays were passed ByRef. I'm sure I read this on the MSDN CD as in: Public Sub getarray(p_Array() as Double) passes a reference to p_Array however, i_Array = p_Array would that not make a copy of p_Array in i_Array? the same as : dim i_Variant as Variant i_Variant = p_Array No? Quote: > hi, i've noticed that there is no way to pass arrays in Vb "really" byref > i mean this: > suppose class A has the method > public sub getarray(byref p_Array() as double) > i_array = p_array 'i_array is an instance variable > exit sub > if i call this method in this way: > dim a1 as new A > dim l_array() as double > redim l_Array(1 to 1000000) as double > for x = 1 to 100000 > l_Array(x) = rnd > next > a1.getarray(l_array) > i can see that the memory grows once when i redim in the caller code (as i > expected) > but i can see that the memory grows again in the line i_array = p_array in > the getarray method and this is not what i want > i would like to avoid the copy of data , in C++ you get this passing a > pointer .. how to do it in VB ? > i remember there are some undocumented functions in Vb about pointer could > they help me ? > TIA,sabba > -- > Enrico Sabbadin > http://sabbadin.tripod.com > MTS FAQ: http://sabbadin.tripod.com/mts_faq.htm
Mon, 08 Jul 2002 03:00:00 GMT

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