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Input bool types to scripts and asBSTR construction


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#1 nihlist   Members   -  Reputation: 122

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Posted 10 March 2004 - 12:28 AM

Hi Andreas, I have been playing with AngelScript for a few days, trying to integrate it with a finite state machine character manager I am putting together. Its nice and compact, was easily wrapped in a C++ wrapper class that does the setup etc, perhaps I can share this if anyone is interested... Anyways, I am having trouble with bool data types, one of the first test cases I am putting together. Assume I have a class (apologies if this doesn't compile, I am typing this in directly, the state machine is somewhat more complex):
class Foo
{
  public:
     Foo();
     Foo(bool newData);
     ~Foo();
     bool getData();

  private:
     bool data;
};
  
With an implementation:
Foo::Foo()
{
  data = false;
}

Foo::Foo(bool newData)
{
  data = newData;
}

~Foo::Foo()
{
}

bool Foo::getData()
{
   return data;
}
  
Pretty useless by itself. If I register the class Foo in the engine and the getData() method as well and pass a pointer to a constructed Foo like such in a script method:
// Start Script

void test(Foo * foo)
{
  if (foo->getData())
  { 
     debug("foo->getData() was true");
  }
  else
  {
     debug("foo->getData() was false");
  }
}

// End Script
  
Where debug is a registered funtion that takes a asBSTR and pipes it to cout on the C++ side It always outputs: foo->getData() was true Even when I set the data value to false. I also tried: if (foo->getData() == true) ... and (foo->getData() == false) ... with no joy. I debugged this further and saw that your bool data type from the dll has: false = 0 true = 255 where MSVC++ 6.0 has false = 0 true = 1 I tried comparing the input bool with an int but the script engine trickily gave me a type conflict message. Thats as far as I got debugging it, any help would be appreciated. Additionally, does anyone know how to create a asBSTR in C++ code to send through to the engine, I know how to use the ones returned, am aware of the dll methods to allocate space for them but can find no examples on how to create a asBSTR from a const char * from the C++ side. Cheers, nihlist To understand recursion you must first understand recursion [edited by - nihlist on March 10, 2004 7:55:20 AM]

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#2 Andreas Jonsson   Moderators   -  Reputation: 3292

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Posted 10 March 2004 - 02:33 AM

I did some debugging, and as it happens you stumbled upon a bug or perhaps a design flaw in AngelScript. MSVC C++ treats the bool type as a 1 byte boolean type, whereas AngelScript treats it as a 4 byte boolean type. When C++ returns the boolean value it does so in the lower 8 bits of EAX, leaving the higher 24 bits with their previous value, meaning that EAX will almost always be different from 0.

Fortunately this is quite easy to fix (changing the AngelScript type to 1 byte as well, should fix the problem), and the next release will have this fix.

In the sample code, available from the angelscript page, there are some functions that return bstrs to the script. Example:

asBSTR bstrFormatInt(int number)
{
acCString str;
str.Format("%d", number);

// We must allocate a new bstr that the script engine will free afterwards
asBSTR bstr = asBStrAlloc(str.GetLength());

memcpy(bstr, str, str.GetLength());

return bstr;
}

Remember that if you receive a bstr by value in the parameters you are responsible to releasing the memory. Therefore I recommend that you always declare your functions to receive bstrs by reference, it would also avoid an internal copy of the bstr.

www.AngelCode.com - game development and more...
AngelScript - free scripting library

#3 Andreas Jonsson   Moderators   -  Reputation: 3292

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Posted 10 March 2004 - 02:39 AM

nihlist, would you mind presenting yourself so that I can credit you for finding the bug? Or do you prefer that I credit you as nihlist?

www.AngelCode.com - game development and more...
AngelScript - free scripting library

#4 nihlist   Members   -  Reputation: 122

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Posted 10 March 2004 - 10:40 AM

Hi Andreas,

Thanks for the quick feedback. I am happy for a credit for this one, my name is Josh Passenger.

nihlist

To understand recursion you must first understand recursion

#5 nihlist   Members   -  Reputation: 122

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Posted 10 March 2004 - 10:43 AM

Oh and thanks for the tips on the asBSTR, I hunted high and low but must have missed this one,

nihlist

To understand recursion you must first understand recursion




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