global and static object

Hello everyone,


This is what mentioned in the book, ATL Internals about why Release function of CComPtr and CComQIPtr is needed for global and static variable.

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The destructor for global and static variable only executes after the main function exits, long after CoUninitialize runs, (That is, if it runs at all. You must link with the C++ runtime library for the constructors and destructors of global and static variable to run.) ATL itself doesn't use the C/C++ runtime library; thus, by default, ATL components don't link with the library.
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I do not quite understand what means "must link with the C++ runtime library for the constructors and destructors ... to run"? Could anyone help please?


thanks in advance,
George

The C runtime library contains some code that looks like this (sort of, it's probably a lot more complicated, and I'm sure the names aren't right - but I'm explaining the principle, not the actual implementation):

Code:

---

int __main(...)
{ 
    int res;
    run_global_constructors();
    res = main(...);
    run_global_destructors();
    return res;
}

---

Of course, if you never link in the __main function, then you are not going to get the global constructors/destructors to run.

static objects are no different from global objects when it comes to construction/destruction - the only difference with static objects is which bits of code can see the variable representing the object.

--
Mats

Thanks Mats,


So, ATL does not have any dependencies of C/C++ Runtime library? I can not imagine code which are composed of C++, which is not using C/C++ Runtime library. Any comments?

Quote:

---

Originally Posted by matsp

The C runtime library contains some code that looks like this (sort of, it's probably a lot more complicated, and I'm sure the names aren't right - but I'm explaining the principle, not the actual implementation):

Code:

---

int __main(...)
{ 
    int res;
    run_global_constructors();
    res = main(...);
    run_global_destructors();
    return res;
}

---

Of course, if you never link in the __main function, then you are not going to get the global constructors/destructors to run.

static objects are no different from global objects when it comes to construction/destruction - the only difference with static objects is which bits of code can see the variable representing the object.

--
Mats

---

regards,
George

Well, I have no idea of how ATL is designed - I've never worked with ATL.

But it's perfectly possible to "use none of the C++ runtime". It just involves avoiding such functions that are part of the C++ runtime.

--
Mats

Thanks Mats,


Let us talk about CRT only this time. :-)

1. What functions are provided by CRT beyond STL?

2. I think when we write console or windows app, it is linked with CRT already, and main/WinMain function is triggered by CRT start point. So, I think in this scenario, since app itself is linked with CRT, ATL used in the app should be able to utilize the CRT's function to call constructor before main and call destructor after main.

I can not think of a scenario when we do not need CRT in a C++ app (even if ATL is not dependent on CRT directly, but ATL is used in the app which could utilize CRT constructor/destructor invocation code indirectly).

Any comments?

Quote:

---

Originally Posted by matsp

Well, I have no idea of how ATL is designed - I've never worked with ATL.

But it's perfectly possible to "use none of the C++ runtime". It just involves avoiding such functions that are part of the C++ runtime.

--
Mats

---

regards,
George

I'm sure it can be done, but you'd have to work hard at it. I think the most likely scenario of not using CRT is if you use ATL for a DLL - in which case you don't really need the CRT for much particularly if you supply your own DLLMain.

--
Mats

Thanks Mats,


1.

I agree for a pure ATL DLL, no CRT and C++ runtime library are needed. But how to you use the DLL, you need to load it into an EXE, right? I think EXE must be dependent on CRT. So, the constructor and destructor can still be called.

2.

Since ATL is not dependent on CRT and C++ Runtime Library, I think ATL is not using any C and C++ functions and classes, like strlen and vector, right?

Quote:

---

Originally Posted by matsp

I'm sure it can be done, but you'd have to work hard at it. I think the most likely scenario of not using CRT is if you use ATL for a DLL - in which case you don't really need the CRT for much particularly if you supply your own DLLMain.

--
Mats

---

regards,
George