destructor | 易学教程

How will _Exit behave in a C++ program?

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问题 C99 offers the _Exit function, which exits "immediately", although it does may close file descriptors. Unix/POSIX extends this behavior by mandating the closing of all fd's without flushing (and offers the synonym _exit). Will these functions call destructors for static objects when called from a C++ program? Does the C++ standard make any guarantees about _Exit ? (Inspired by this question; I suddenly wondered what happens in the typical fork - exec - _exit idiom in C++.) 回答1: It simply

Pseudo-destructor call does not destroy an object

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Consider the following code: #include <iostream> typedef int t; t a=42; int main() { a.t::~t(); std::cout << a; //42 } I'm expected that a will be destroyed. But it is not true, why? How does do that pseudo-destructor call will be destroyed the object? Columbo But it is not true, why? §5.2.4/1: The only effect is the evaluation of the postfix-expression before the dot or arrow. Where the postfix-expression is the expression of the object for which the call takes place. Thus a pseudo destructor call, as a call to a trivial destructor, does not end the lifetime of the object it is applied to.

The difference between a destructor and a finalizer?

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问题 Please Note: This question is about the difference in terminology between the words "destructor" and "finalizer" and their correct usage. I have merely provided examples of their use in C# and C++/CLI to demonstrate why I am asking the question. I am well aware of how it is implemented in both C# and the CLR, but I am asking about the correct use of terminology. In the C# world the terms "destructor" and "finalizer" seem to be used pretty much interchangeably, which I suspect is because the C

How to destroy an object?

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As far as I know (which is very little) , there are two ways, given: $var = new object() Then: // Method 1: Set to null $var = null; // Method 2: Unset unset($var); Other better method? Am I splitting hairs here? Frankie You're looking for unset() . But take into account that you can't explicitly destroy an object. It will stay there, however if you unset the object and your script pushes PHP to the memory limits the objects not needed will be garbage collected. I would go with unset() (as opposed to setting it to null) as it seems to have better performance (not tested but documented on one

Destructors of builtin types (int, char etc..)

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In C++ the following code gives a compiler error: void destruct1 (int * item) { item->~int(); } This code is nearly the same, I just typedef the int to another type and something magic happens: typedef int myint; void destruct2 (myint * item) { item->~myint(); } Why does the second code work? Does an int get a destructor just because it has been typedefed? In case you wonder why one ever would like to do this: This comes from refactoring C++ code. We're removing the standard heap and replacing it with selfmade pools. This requires us to call placement-new and the destructors. I know that

Php Destructors

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问题 Please give me some real life examples when you had to use __destruct in your classes. 回答1: Ok, since my last answer apparently didn't hit the mark, let me try this again. There are plenty of resources and examples on the internet for this topic. Doing a bit of searching and browsing other framework's code and you'll see some pretty good examples... Don't forget that just because PHP will close resources on termination for you doesn't mean that it's bad to explictly close them when you no

What is the order in which the destructors and the constructors are called in C++

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问题 What is the order in which the destructors and the constructors are called in C++? Using the examples of some Base classes and Derived Classes 回答1: The order is: Base constructor Derived constructor Derived destructor Base destructor Example: class B { public: B() { cout<<"Construct B"<<endl; } virtual ~B() { cout<<"Destruct B"<<endl; } }; class D : public B { public: D() { cout<<"Construct D"<<endl; } virtual ~D() { cout<<"Destruct D"<<endl; } }; int main(int argc, char **argv) { D d; return

I can't get dealloc be called when deleting an object

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问题 I have the following C++ class : .H class ALabSet: public LabSet { public: PyObject *m_obj; ALabSet(PyObject *obj); virtual ~ALabSet(); PyObject *GetPyObj(); }; .CPP ALabSet::ALabSet(PyObject *obj): LabSet() { this->m_obj = obj; // Provided by "cyelp_api.h" if (import_cyelp()) { } else { Py_XINCREF(this->m_obj); } } ALabSet::~ALabSet() { Py_XDECREF(this->m_obj); } PyObject *ALabSet::GetPyObj() { return this->m_obj; } I exposed it as follows with Cython : cdef extern from "adapter

using python WeakSet to enable a callback functionality

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问题 I'm investigating if I can implement an easy callback functionality in python. I thought I might be able to use weakref.WeakSet for this, but there is clearly something I'm missing or have misunderstood. As you can see in the code I first tried with a list of call back methods in 'ClassA' objects, but realized that this would keep objects that have been added to the list of callbacks alive. Instead I tried using weakref.WeakSet but that doesnt do the trick either (at least not en this way).

Why is the destructor of the class called twice?

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Apologies if the question sounds silly, I was following experts in SO and trying some examples myself, and this is one of them. I did try the search option but didn't find an answer for this kind. class A { public: A(){cout<<"A Contruction"<<endl;} ~A(){cout<<"A destruction"<<endl;} }; int main() { vector<A> t; t.push_back(A()); // After this line, when the scope of the object is lost. } Why is the destructor of the class called twice ? To add the element a copy constructor is invoked on a temporary object. After the push_back() the temporary object is destroyed - that't the first destructor