VB Syntax, Declaring an array of pointers in Visual Basic (and putting and getting data from it)

Declaring an array of pointers in Visual Basic (and putting and getting data from it)

Author	Message
Hans Rasmusse #1 / 8	Declaring an array of pointers in Visual Basic (and putting and getting data from it) Declaring an array of pointers in Visual Basic (and putting and getting data from it)? I have not succeeded in solving a problem calling a DLL from Visual Basic. ANY help appreciated especially if it is impossible, or maybe it isn't??? The C declaration looks like this: #define PBRETURN long int PBRETURN WINAPI pbEnrollWiz(OUT void templ[10]); As I understand the parameter that receives data from the function is an array of pointers. I also know that each entry in the array is a pointer to either NULL or the pointer is referencing memory allocated by malloc(1868); I also know that the DLL and function will use the allocated memory to write binary data for each pointer (of the 10 possible) that is not NULL. In Visual Basic I therefore need to create an array with 10 entries. Each entry should be a pointer to a memory area of 1868 bytes or point to NULL (no memory allocated). It's the duty of program to decide with of the 10 entries I want to receive data in. There are several difficulties when trying to do this in VB: 1. How do I declare an array of pointers? Can this even be done? 2. How do I make sure that some pointers should be NULL and at least one pointer I need to reference to an area of 1868 bytes that is allocated with malloc(1868)? There is no malloc() in Visual Basic. 3. The data received back is not text it's binary data. How can I store this? This might be a clue when building the array. Byte datatype in Visual Basic only allows me to store 1 byte. Maybe an array of bytes in a Type Declaration? I really really really hope someone has any clues. If you have anything to add please do so. You do not need to come up with a complete solution. Sometimes a few tips might help. I have some tips already but since everything I try result in a DLL-crash I want to clear my mind totally and start over with fresh idas. Down below is an example in C calling the Function as described above. PBRETURN ret_val; void enrolled_template[10] = {NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL}; // All pointers point to NULL enrolled_template[6] = malloc(1868); // Pointer 6 is initialized with malloc() to point to an area large enough for function pbEnrollWiz ret_val = pbEnrollWiz(enrolled_template); // pbEnrollWiz will detect that Pointer 6 has allocated space and will write back some data to the memory
Mon, 12 Aug 2002 03:00:00 GMT

Stephe #2 / 8	Declaring an array of pointers in Visual Basic (and putting and getting data from it) Quote: > Declaring an array of pointers in Visual Basic (and putting and getting data > from it)? I'm afraid your'e going to have some problems with this, as VB doesn't provide any built in support for pointers, dynamicly allocated memory or directly accessing memory. All you can do is get a pointer to IUnknown of an object, (ObjPtr), a string (StrPtr), and to a variant (VarPtr). Apart from that, you can store pointers in longs and pass them to DLLs. Thats it. Stephen
Mon, 12 Aug 2002 03:00:00 GMT

D Heste #3 / 8	Declaring an array of pointers in Visual Basic (and putting and getting data from it) You would probably have better luck using separate parameters for each value instead of passing an array. In C++ you could do long WINAPI MyFunc(char rtn1,char rtn2,char rtn3... char rtn10) { build the 10 array entries memcpy(rtn1,the first array entry,1868); .... memcpy(rtn10,the 10th array entry,1868); return 1; Quote: } In VB you could do private declare myfunc lib "mylib.dll" (byval rtn1$,byval rtn2$,byval rtn3$ ... byval rtn10$) as long Then when you call the function in VB do: dim rtn1$,rtn2$,rtn3$ ...,rtn10$ rtn1=space(1869) rtn2=space(1869) .... rtn10=space(1869) if MyFunc(rtn1,rtn2 ...rtn10)<>0 then now you have your 10 1868 byte arrays in rtn1..rtn10. endif I can't remember if I've tried it before, but you may be able to do: dim r$(10) for i=1 to 10: r(i)=space(1869) : next if MyFunc(r(1),r(2),r(3),...r(10)) <>0 then for i=1 to 10 dowhateverwith r(i) next endif Another (cleaner) possibility: In C++ do for (int i=0;i<10;i++,ix+=1868) memcpy(rtnValue+ix, array[i], 1868) and in VB do dim r$ r = space(186810) MyFunc r for i=1 to 186810 step 1868 dowhateverwith mid(r,i,1868) Good luck -Dwain Quote: > Declaring an array of pointers in Visual Basic (and putting and getting data > from it)? > I have not succeeded in solving a problem calling a DLL from Visual Basic. > ANY help appreciated especially if it is impossible, or maybe it isn't??? > The C declaration looks like this: > #define PBRETURN long int > PBRETURN WINAPI > pbEnrollWiz(OUT void templ[10]); > As I understand the parameter that receives data from the function is an > array of pointers. I also know that each entry in the array is a pointer to > either NULL or the pointer is referencing memory allocated by malloc(1868); > I also know that the DLL and function will use the allocated memory to write > binary data for each pointer (of the 10 possible) that is not NULL. > In Visual Basic I therefore need to create an array with 10 entries. Each > entry should be a pointer to a memory area of 1868 bytes or point to NULL > (no memory allocated). It's the duty of program to decide with of the 10 > entries I want to receive data in. > There are several difficulties when trying to do this in VB: > 1. How do I declare an array of pointers? Can this even be done? > 2. How do I make sure that some pointers should be NULL and at least one > pointer I need to reference to an area of 1868 bytes that is allocated with > malloc(1868)? There is no malloc() in Visual Basic. > 3. The data received back is not text it's binary data. How can I store > this? This might be a clue when building the array. Byte datatype in Visual > Basic only allows me to store 1 byte. Maybe an array of bytes in a Type > Declaration? > I really really really hope someone has any clues. If you have anything to > add please do so. You do not need to come up with a complete solution. > Sometimes a few tips might help. I have some tips already but since > everything I try result in a DLL-crash I want to clear my mind totally and > start over with fresh idas. > Down below is an example in C calling the Function as described above. > PBRETURN ret_val; > void enrolled_template[10] = {NULL, NULL, NULL, NULL, NULL, > NULL, NULL, NULL, NULL, NULL}; // All > pointers point to NULL > enrolled_template[6] = malloc(1868); // Pointer 6 is initialized with > malloc() to point to an area large enough for function pbEnrollWiz > ret_val = pbEnrollWiz(enrolled_template); // pbEnrollWiz will detect that > Pointer 6 has allocated space and will write back some data to the memory
Mon, 12 Aug 2002 03:00:00 GMT

Mr. #4 / 8	Declaring an array of pointers in Visual Basic (and putting and getting data from it) true, you can not declare (or use) pointers in VB, but if you are using VB6 you can use the AddressOf operator to pass the address to the C function. you can look it up at MSDN online for more info on it. Mr. X Quote: >> Declaring an array of pointers in Visual Basic (and putting and getting >data >> from it)? >I'm afraid your'e going to have some problems with this, as VB doesn't >provide any built in support for pointers, dynamicly allocated memory or >directly accessing memory. All you can do is get a pointer to IUnknown of an >object, (ObjPtr), a string (StrPtr), and to a variant (VarPtr). Apart from >that, you can store pointers in longs and pass them to DLLs. Thats it. >Stephen
Tue, 13 Aug 2002 03:00:00 GMT

Larry Brasfiel #5 / 8	Declaring an array of pointers in Visual Basic (and putting and getting data from it) Quote: > Declaring an array of pointers in Visual Basic (and putting and getting data > from it)? > I have not succeeded in solving a problem calling a DLL from Visual Basic. > ANY help appreciated especially if it is impossible, or maybe it isn't??? > The C declaration looks like this: > #define PBRETURN long int > PBRETURN WINAPI > pbEnrollWiz(OUT void *templ[10]); [big snip of difficulties had already] If the C interface is frozen, you have an impossible task. If that interface was intended to be useful to the VB programmer, the person who wrote it needs an education. If that person sold you the DLL with the claim it was usable from VB, get a refund. The basic problem (pun intended) is that VB is a programmer-proof environment. Untyped pointers are simply not allowed and the only "untyped" type is a type-tagged data object. (Variant) Arrays are represented using a structure with appended bounds and a dynamically sized data block, (SAFEARRAY), except for fixed size arrays embedded in UDT's. If you have control of that C interface, redefine it to be compatible with VB data types. You have much more flexibility dealing with those from the C end than dealing with untyped data from the VB end. If you do not have control of the interface, VB is simply the wrong tool for running that DLL. -- Larry Brasfield Above opinions may be mine alone.
Tue, 13 Aug 2002 03:00:00 GMT

Alexander Kienzl #6 / 8	Declaring an array of pointers in Visual Basic (and putting and getting data from it) Well, I like using pointers in C, but I don't like them in VB. Anyway, nearly everything is possible... You can use CopyMemory API to move memory around. Public Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (Destination As Any, Source As Any, ByVal Length As Long) To copy the memory where a pointer points to, pass the pointer ByVal. Hope this helps Alex Quote: > > Declaring an array of pointers in Visual Basic (and putting and getting data > > from it)? > > I have not succeeded in solving a problem calling a DLL from Visual Basic. > > ANY help appreciated especially if it is impossible, or maybe it isn't??? > > The C declaration looks like this: > > #define PBRETURN long int > > PBRETURN WINAPI > > pbEnrollWiz(OUT void *templ[10]); > [big snip of difficulties had already] > If the C interface is frozen, you have an impossible > task. If that interface was intended to be useful to > the VB programmer, the person who wrote it needs > an education. If that person sold you the DLL with > the claim it was usable from VB, get a refund. > The basic problem (pun intended) is that VB is a > programmer-proof environment. Untyped pointers > are simply not allowed and the only "untyped" type > is a type-tagged data object. (Variant) Arrays are > represented using a structure with appended bounds > and a dynamically sized data block, (SAFEARRAY), > except for fixed size arrays embedded in UDT's. > If you have control of that C interface, redefine it to > be compatible with VB data types. You have much > more flexibility dealing with those from the C end > than dealing with untyped data from the VB end. > If you do not have control of the interface, VB is > simply the wrong tool for running that DLL. > -- > Larry Brasfield > Above opinions may be mine alone.
Tue, 13 Aug 2002 03:00:00 GMT

Martin Adou #7 / 8	Declaring an array of pointers in Visual Basic (and putting and getting data from it) From the top of my head (code based in C sample): 'PBRETURN WINAPI 'pbEnrollWiz(OUT void templ[10]); 'I assume PBRETURN is a long Declare Function pbEnrollWiz lib "IDontKnow.dll" (lPointers() As Long) As Long Dim abPosition1() As Byte . . . Dim abPosition10() As Byte 'void enrolled_template[10] = {NULL, NULL, NULL, NULL, NULL,NULL, NULL, NULL, NULL, NULL}; // All Dim abaArrayToPassToTheFunction(1 To 10) As long 'enrolled_template[6] = malloc(1868); // Pointer 6 is initialized with 'malloc() to point to an area large enough for function pbEnrollWiz Redim abPosition6(1868) abaArrayToPassToTheFunction(1) = 0 . . abaArrayToPassToTheFunction(6) = VarPtr(abPosition6(0)) . . abaArrayToPassToTheFunction(10) = Quote: >ret_val = pbEnrollWiz(enrolled_template); // pbEnrollWiz will detect that >Pointer 6 has allocated space and will write back some data to the memory lRet = pbEnrollWiz(abaArrayToPassToTheFunction()) Let me know if it worked. Martin Quote: >Declaring an array of pointers in Visual Basic (and putting and getting data >from it)? >I have not succeeded in solving a problem calling a DLL from Visual Basic. >ANY help appreciated especially if it is impossible, or maybe it isn't??? >The C declaration looks like this: >#define PBRETURN long int >PBRETURN WINAPI >pbEnrollWiz(OUT void templ[10]); >As I understand the parameter that receives data from the function is an >array of pointers. I also know that each entry in the array is a pointer to >either NULL or the pointer is referencing memory allocated by malloc(1868); >I also know that the DLL and function will use the allocated memory to write >binary data for each pointer (of the 10 possible) that is not NULL. >In Visual Basic I therefore need to create an array with 10 entries. Each >entry should be a pointer to a memory area of 1868 bytes or point to NULL >(no memory allocated). It's the duty of program to decide with of the 10 >entries I want to receive data in. >There are several difficulties when trying to do this in VB: >1. How do I declare an array of pointers? Can this even be done? >2. How do I make sure that some pointers should be NULL and at least one >pointer I need to reference to an area of 1868 bytes that is allocated with >malloc(1868)? There is no malloc() in Visual Basic. >3. The data received back is not text it's binary data. How can I store >this? This might be a clue when building the array. Byte datatype in Visual >Basic only allows me to store 1 byte. Maybe an array of bytes in a Type >Declaration? >I really really really hope someone has any clues. If you have anything to >add please do so. You do not need to come up with a complete solution. >Sometimes a few tips might help. I have some tips already but since >everything I try result in a DLL-crash I want to clear my mind totally and >start over with fresh idas. >Down below is an example in C calling the Function as described above. >PBRETURN ret_val; >void enrolled_template[10] = {NULL, NULL, NULL, NULL, NULL, > NULL, NULL, NULL, NULL, NULL}; // All >pointers point to NULL >enrolled_template[6] = malloc(1868); // Pointer 6 is initialized with >malloc() to point to an area large enough for function pbEnrollWiz >ret_val = pbEnrollWiz(enrolled_template); // pbEnrollWiz will detect that >Pointer 6 has allocated space and will write back some data to the memory
Wed, 14 Aug 2002 03:00:00 GMT

Hans Rasmusse #8 / 8	Declaring an array of pointers in Visual Basic (and putting and getting data from it) You are absolutely right! I thank you a lot. It was not 100% accurate but 99% at least:-). But you should have all credit for the success. VarPtr() opened up a lot of possibilites. Too bad VarPtr() is not documented in VB so I took some time reading about how the function and it's siblings work. There are more hidden functions for you guys to use when dealing with strings and objects or other complex datastructures. I hade to make a few changes before it worked but you really gave me the clue in how to bend the memory to the max in Visual Basic. I was so e{filter}d I forgot to go to sleep last night efter you gave me the tip. Now I have 100% functionality of my application. I can tell you that the API that I had to call required more use of VarPtr() so I was really thrilled when I was reminded of it. I have not really used VB this intense since 2 years ago but I'm pretty sure that I have been using VarPtr() before when making a callback function with the AddressOf operator among others. --------------- For you new into VB make sure that when you define arrays check if Option Base is 0 or 1. It defaults to 0 so if you write Dim x(10) you get one array with 11 elements and not 10 as you might think. This is important to know so you don't unaccidentally overwrite something in the memory and cause a program crash. It happened to me as I was working with VarPtr(). --------------- Anyway this is how it should look like: Public Declare MyFunction lib="libraryname" (ByVal lPointers As Long) As Long // Important to declare as ByVal if not VB will send the reference since ByRef is default (this was one of the things I have to change) and also I decided not to write lPointers() as an array it did not work so I changed to sending the pointer to the array instead as you can see down below. --------------- // I need to declare the store of bytes Dim byteStore() As Byte // Byte store Dim myArray() As Long // The array which will contain references to the byte stores defined below Dim lReturn As Long Redim byteStore(1868 -1) // Subract one since option base is 0 so we get an interval of 0-1867 Redim myArray(10 - 1) // I want 10 entries (one for each finger on your 2 hands) myArray(6) = VarPtr(byteStore(0)) // Make sure that array will include the pointer to the byteStore before calling function // All other entries in myArray will be 0 and not point to anything lReturn = MyFunction(VarPtr(myArray(0))) // This is the call and the API will be notified of the address of myArray // And find that index 6 has a pointer to byteStore which contains 1868 bytes // ready to recieve data // Once again Martin this I had to change to VarPtr() again // since the array did not seem // to be acknowledged by the API. Once again, thank you Martin for you excellent knowledge! --------------- Hans Rasmussen Quote: > Declaring an array of pointers in Visual Basic (and putting and getting data > from it)? > I have not succeeded in solving a problem calling a DLL from Visual Basic. > ANY help appreciated especially if it is impossible, or maybe it isn't??? > The C declaration looks like this: > #define PBRETURN long int > PBRETURN WINAPI > pbEnrollWiz(OUT void templ[10]); > As I understand the parameter that receives data from the function is an > array of pointers. I also know that each entry in the array is a pointer to > either NULL or the pointer is referencing memory allocated by malloc(1868); > I also know that the DLL and function will use the allocated memory to write > binary data for each pointer (of the 10 possible) that is not NULL. > In Visual Basic I therefore need to create an array with 10 entries. Each > entry should be a pointer to a memory area of 1868 bytes or point to NULL > (no memory allocated). It's the duty of program to decide with of the 10 > entries I want to receive data in. > There are several difficulties when trying to do this in VB: > 1. How do I declare an array of pointers? Can this even be done? > 2. How do I make sure that some pointers should be NULL and at least one > pointer I need to reference to an area of 1868 bytes that is allocated with > malloc(1868)? There is no malloc() in Visual Basic. > 3. The data received back is not text it's binary data. How can I store > this? This might be a clue when building the array. Byte datatype in Visual > Basic only allows me to store 1 byte. Maybe an array of bytes in a Type > Declaration? > I really really really hope someone has any clues. If you have anything to > add please do so. You do not need to come up with a complete solution. > Sometimes a few tips might help. I have some tips already but since > everything I try result in a DLL-crash I want to clear my mind totally and > start over with fresh idas. > Down below is an example in C calling the Function as described above. > PBRETURN ret_val; > void enrolled_template[10] = {NULL, NULL, NULL, NULL, NULL, > NULL, NULL, NULL, NULL, NULL}; // All > pointers point to NULL > enrolled_template[6] = malloc(1868); // Pointer 6 is initialized with > malloc() to point to an area large enough for function pbEnrollWiz > ret_val = pbEnrollWiz(enrolled_template); // pbEnrollWiz will detect that > Pointer 6 has allocated space and will write back some data to the memory
Fri, 16 Aug 2002 03:00:00 GMT

Page 1 of 1

[ 8 post ]