Learn how to detect Stack Unwinding in a Destructor in C++?

What’s Stack Unwinding?

Stack unwinding is the method of executing destructors for all native objects when an exception propagates out of a perform. It occurs when an exception is thrown and never caught inside the identical perform. When this happens, the destructors for all objects with computerized storage length declared in that perform are known as in reverse order of their declaration earlier than the management is transferred to a handler (if any) or returned to the caller.

Stack unwinding is often clear to the programmer and occurs mechanically. Stack Unwinding is usually related to Exception Dealing with. When an exception happens in C++, the perform name stack is linearly looked for the exception handler, and any entries earlier than the perform with the exception handler are eradicated. If an exception shouldn’t be dealt with in the identical code, stack unwinding is required (the place it’s thrown). Stack unwinding is basically the method of invoking the destructors for all automated objects created at run time (at any time when an exception is thrown).

Other ways to method Stack Unwinding:

There are other ways of approaching the subject of stack unwinding in a destructor.

A method is to have a look at it from the angle of what occurs when an exception is thrown.
One other approach is to have a look at it from the angle of how a destructor is known as when an object goes out of scope.

Taking a look at stack unwinding from the angle of an exception being thrown might help us perceive why it is very important have a destructor that may clear up after itself.

When an exception is thrown:

This system execution jumps to the closest catch block. However earlier than that occurs, all of the objects that have been created within the attempt block are destroyed. This consists of any native objects in addition to any objects that have been created by dynamic reminiscence allocation. If the destructors for these objects don’t correctly clear up, then it may possibly result in reminiscence leaks or different issues.

From the angle of how a destructor is known as:

It may well assist to grasp the significance of a destructor. A destructor is known as at any time when an object goes out of scope. When an object goes out of scope, its destructor is known as and any sources that it was utilizing are freed up. If the destructor doesn’t correctly clear up, then it may possibly result in useful resource leaks or different issues.

Learn how to Detect Stack Unwinding?

In a destructor, stack unwinding will be detected by on the lookout for indicators of cleanup exercise, comparable to the next:

Invoking features that launch sources (e.g. shut information or free reminiscence)
Logging messages
Setting flags

If any of those actions are noticed in a destructor, it’s possible that stack unwinding is happening.

Utilizing the std::uncaught_exception()

You need to use the std::uncaught_exception() perform which returns true if an exception is at the moment being dealt with (i.e. thrown however not but caught). So, in your destructor, you’d examine if std::uncaught_exception() returns true or false and take acceptable motion accordingly.

Instance:

C++

#embody <bits/stdc++.h>

utilizing namespace std;

class MyClass {

public:

MyClass()

{

}

~MyClass()

{

if (!std::uncaught_exception()) {

}

};

Overriding std::terminate() perform

With a view to detect when stack unwinding is going on, you’ll be able to override the std::terminate() perform. The runtime calls this perform when it can’t discover a appropriate exception handler. By overriding std::terminate(), you’ll be able to set a breakpoint or log a message to assist debug your program.

Right here is an instance of how you’d override std::terminate():

C++

void my_terminate()

{

std::cerr << "Stack unwinding detected!" << std::endl;

std::terminate();

}

int essential()

{

std::set_terminate(my_terminate);

attempt {

}

catch (...) {

}

return 0;

}

By setting a flag within the constructor:

Set a flag within the constructor and examine that flag within the destructor. If the flag is ready, then you recognize that the destructor was known as due to an exception. Right here is an instance:

C++

class MyClass {

public:

MyClass()

: m_isUnwinding(false)

{

}

~MyClass()

{

if (m_isUnwinding) {

}

else {

}