www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - array error

reply hrk <l8atnight gmail.com> writes:
Hi,

I have a class STATUS, in which i do have an dynamic array

class STATUS {
private:
int mVector[];
public:
int* StatusHandle() {
    return cast(int*) this.mVector.ptr;
  }
bool Errors() {
    ...
 }
int SqlCode() {
...
}
  int EngineCode() {
...
}
void Reset() {
  mVector[] = 0;
}
this(int asize) {
   mVector.length = asize;
    mVector[] = 0;
}
  string ErrorMessage() {
...
}
}

The method  StatusHandle() returns a pointer that is the input for a function
in a “C” DLL. 

The class is newed, along with other classes of this kind (STATUS), in an other
classes method:

bool Connect(string dbname, string username, string password, string RoleName =
"", string CharSet = "") {
      auto status = new STATUS(200);
.........
......... 
cresult = isc_database_info(status.StatusHandle(), &db, 3, cast(char*)
items.ptr, 200, result.ResultHandle());
.........
.........
.........
}

The class (STATUS) instances will function a couple of times, but than they
crash unpredictably. 
Can anyone tell me what i am doing wrong? I need the memory of the array
(mVector) to be contiguous and it’s content should only change through the
manipulation of the pointer  StatusHandle() by the “C” DLL functions. I need
sometimes several instances of the class STATUS that are created in some other
class.
I am using 2.0 and phobos.
Jul 20 2008
parent reply "Koroskin Denis" <2korden gmail.com> writes:
On Sun, 20 Jul 2008 12:18:18 +0400, hrk <l8atnight gmail.com> wrote:


 Hi,

 I have a class STATUS, in which i do have an dynamic array

 class STATUS {
 private:
 int mVector[];
 public:
 int* StatusHandle() {
     return cast(int*) this.mVector.ptr;
   }
 bool Errors() {
     ...
  }
 int SqlCode() {
 ...
 }
   int EngineCode() {
 ...
 }
 void Reset() {
   mVector[] = 0;
 }
 this(int asize) {
    mVector.length = asize;
     mVector[] = 0;
 }
   string ErrorMessage() {
 ...
 }
 }

 The method  StatusHandle() returns a pointer that is the input for a  
 function in a “C” DLL.

 The class is newed, along with other classes of this kind (STATUS), in  
 an other classes method:

 bool Connect(string dbname, string username, string password, string  
 RoleName = "", string CharSet = "") {
       auto status = new STATUS(200);
 .........
 .........
 cresult = isc_database_info(status.StatusHandle(), &db, 3, cast(char*)  
 items.ptr, 200, result.ResultHandle());
 .........
 .........
 .........
 }

 The class (STATUS) instances will function a couple of times, but than  
 they crash unpredictably.
 Can anyone tell me what i am doing wrong? I need the memory of the array  
 (mVector) to be contiguous and it’s content should only change through  
 the manipulation of the pointer  StatusHandle() by the “C” DLL  
 functions. I need sometimes several instances of the class STATUS that  
 are created in some other class.
 I am using 2.0 and phobos.


There are a few problems in your code. First of all, string is an  
immutable class by design. You should not cast away its constness.  
Instead, use char[], which is mutable. In fact string is an alias (kindof  
typedef in C++) to invariant(char)[], i.e. an array of immutable chars.

Second, strings (and char[]) are not null-terminated, otherwise strind (or  
any other array) slicing wouldn't work. That's why you should ensure that  
0 is appended to your string. There are two ways to do so:

1) do this but calling toStringz(items): isc_database_info(..., ..., ...,  
toStringz(items), ..., ...);
2) if and only if you are sure that this C function doesn't mutate your  
string, you can append the 0 manually:
items ~= 0;
// you can guarantee that string won't be changed through pointer
isc_database_info(..., ..., ..., cast(char*)items.ptr, ..., ...);

Apart from that I don't see any issue with your STATUS class. Just two  
notes:
- you may declare protection attributes on each class member individually,  
like "private int mVector[];".
- you can declare array like "int mVector[];" as well as "int[] mVector;".
Jul 20 2008
parent reply bearophile <bearophileHUGS lycos.com> writes:
Koroskin Denis:

 - you can declare array like "int mVector[];" as well as "int[] mVector;".


I don't agree, the right way to declare it in D is "int[] mVector;".

The other way is just for code translated from C (and to confuse programmers.
As the Zen of another language says: "There should be one-- and preferably only
one --obvious way to do it."  So I'd probably like to remove that syntax).

Bye,
bearophile
Jul 20 2008
parent reply "Koroskin Denis" <2korden gmail.com> writes:
On Sun, 20 Jul 2008 16:09:38 +0400, bearophile <bearophileHUGS lycos.com>  
wrote:


 Koroskin Denis:

 - you can declare array like "int mVector[];" as well as "int[]  
 mVector;".


 I don't agree, the right way to declare it in D is "int[] mVector;".

 The other way is just for code translated from C (and to confuse  
 programmers. As the Zen of another language says: "There should be one--  
 and preferably only one --obvious way to do it."  So I'd probably like  
 to remove that syntax).

 Bye,
 bearophile


I just didn't want to push the guy too much :)
Experience comes with time. It's too hard to change habits at once.
Jul 20 2008
parent hrk <l8atnight gmail.com> writes:
yep, true - don't push me to much.

it seems like you are right, the program should work. funny so, when i move an
array with initialization declaration up or down in the code, the program
excepts at different places, without that the array is used. seems like an
error in the compiler.

i am tring to port a c++ library for firebird to d, since i think that the db
support needs some more libraries. gui is ok for me but alot of the rest is
missing for d.

thank you guys for the replies and the help you offered!

hrk


Koroskin Denis Wrote:


 On Sun, 20 Jul 2008 16:09:38 +0400, bearophile <bearophileHUGS lycos.com>  
 wrote:
 

 Koroskin Denis:

 - you can declare array like "int mVector[];" as well as "int[]  
 mVector;".


 I don't agree, the right way to declare it in D is "int[] mVector;".

 The other way is just for code translated from C (and to confuse  
 programmers. As the Zen of another language says: "There should be one--  
 and preferably only one --obvious way to do it."  So I'd probably like  
 to remove that syntax).

 Bye,
 bearophile


 
 I just didn't want to push the guy too much :)
 Experience comes with time. It's too hard to change habits at once.
Jul 21 2008