topic Re: AcString? in ObjectARX Forum

AcString?

Anonymous — Mon, 28 Nov 2016 21:01:28 GMT

const ACHAR* WhatIsReturned()
{
      AcString a = L"Test";
      AcString b = L" this";
      AcString c = a + b;
      return c;
}

What happens to c when this method returns. Does the underlying string encapsulated by c get lost when c goes out of scope or is a copy of the const ACHAR* returned?

Mike

Re: AcString?

Alexander.Rivilis — Mon, 28 Nov 2016 21:13:48 GMT

After return from this function destructor of "c" do returned pointer invalid. You do not use such code. IMHO.

Re: AcString?

owenwengerd — Tue, 29 Nov 2016 01:22:02 GMT

Memory for all three local strings is freed before the function returns. The code is not correct.

Re: AcString?

Anonymous — Tue, 29 Nov 2016 12:17:43 GMT

Yeah, I figured as much, but I was thinking that one of the overloads would return a new ACHAR*. I realized after I posted that this was a "cloudy mind moment" realizing that even if a new ACHAR* was returned, there was no way to free it. Will a AcString be returned by value? Or would that be freed as well.

AcString TestThis()
{
    AcString a = L"Test";
    AcString b = L" this!";
    AcString c = a + b;

    return c;
}

In this code, would 'c' be returned by value or would it still go out of scope?

Mike

Re: AcString?

Alexander.Rivilis — Tue, 29 Nov 2016 12:35:16 GMT

@Anonymous wrote:

Yeah, I figured as much, but I was thinking that one of the overloads would return a new ACHAR*. I realized after I posted that this was a "cloudy mind moment" realizing that even if a new ACHAR* was returned, there was no way to free it. Will a AcString be returned by value? Or would that be freed as well.
AcString TestThis()
{
    AcString a = L"Test";
    AcString b = L" this!";
    AcString c = a + b;

    return c;
}
In this code, would 'c' be returned by value or would it still go out of scope?

Mike

In this code compile create copy of 'c' and return it. After that destructor of 'c' will be called. So you have a valid value of 'c' after calling TestThis():

AcString d = TestThis();

Re: AcString?

owenwengerd — Tue, 29 Nov 2016 14:36:46 GMT

It's common to return AcString by value, but functions should almost never accept string arguments as AcString by value. Almost always, string arguments should be typed as const ACHAR* or at least const AcString&. Example (untested):

AcString myConcatStr1(const ACHAR* in1, const ACHAR* in2)
{
  AcString in1Str(in1);
  return in1Str + in2;
}

AcString myConcatStr2(const AcString& in1Str, const AcString& in2Str)
{
  return in1Str + in2Str;
}

void test()
{
  AcString s1 = _ACRX_T("Test");
  AcString s2 = _ACRX_T(" String");
  AcString s3 = myConcatStr1(s1, s2);
  AcString s4 = myConcatStr2(s1, s2);
}