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POWhy do c++ instances automatically call constructor and destructor when called via Objective-c classes?
 

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  1. POWhy do c++ instances automatically call constructor and destructor when called via Objective-c classes?
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    <p>I have a question:</p> <p>I don't explicitly "<code>new</code>" and "<code>delete</code>" my C++ instance, but it automatically calls "<code>new</code>" and "<code>delete</code>" when the objective-c class init. Any idea?</p> <pre><code>class myCppTestClass { public: myCppTestClass() { NSLog(@"MyCpp constructor"); } ~myCppTestClass() { NSLog(@"MyCpp destructor"); } }; @interface MyTestClass : NSObject { myCppTestClass myCppInstance; } @end @implementation MyTestClass @end </code></pre> <p>And I call it like this:</p> <pre><code>NSLog(@"Create an object."); MyTestClass *objcObject = [[MyTestClass alloc] init]; NSLog(@"Object created"); [objcObject release]; objcObject = nil; NSLog(@"Object released."); </code></pre> <p>Then I run it, the log is like this:</p> <pre><code>2012-11-16 12:01:18.747 iOSVersion[87248:f803] Create an object. 2012-11-16 12:01:18.749 iOSVersion[87248:f803] MyCpp constructor 2012-11-16 12:01:18.750 iOSVersion[87248:f803] Object created 2012-11-16 12:01:18.751 iOSVersion[87248:f803] MyCpp destructor 2012-11-16 12:01:18.752 iOSVersion[87248:f803] Object released. </code></pre> <p>It's not about Automatic Reference Counnting, because it is closed, any ideas? Thank you so much.</p> <p>Again, if MyTestClass is like this, the constructor and destructor will not been called:</p> <pre><code>@interface MyTestClass : NSObject { myCppTestClass * myCppInstance; } </code></pre> <p>and the log:</p> <pre><code>2012-11-16 12:22:38.710 iOSVersion[87428:f803] Create an object. 2012-11-16 12:22:38.711 iOSVersion[87428:f803] Object created 2012-11-16 12:22:38.712 iOSVersion[87428:f803] Object released. </code></pre>
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      1. POWhy do c++ instances automatically call constructor and destructor when called via Objective-c classes?
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    1. COIt's just how c++ objects work when they aren't pointers or references.
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      1. POWhy do c++ instances automatically call constructor and destructor when called via Objective-c classes?
      1. USRichard J. Ross III
    2. COYou mean `myCppTestClass myCppInstance;` ?
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      1. POWhy do c++ instances automatically call constructor and destructor when called via Objective-c classes?
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    3. COyes, the variable declaration causes the default constructor to be invoked when the object is allocated, through some runtime wizardry.
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      1. POWhy do c++ instances automatically call constructor and destructor when called via Objective-c classes?
      1. USRichard J. Ross III
 

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