CODEWITHSUNDEEP
c++destructor
mr_T
mr_T

Reputation: 2621

Will the destructor of an object be called if a function returns early or throws an exception?

In the following code, I use a wrapper object to temporarily store some stuff from a db in memory. My question is simple:

Can I be sure that the destructor is called? I am particularly worried about cases where a) testCondition is true and the function returns early from an inner scope of the scope in which tempObj was constructed b) some runtime error occurs during the execution of this function (which is caught at a higher level)

(As a side question: is this a good way to temporarily store some data? In my application, someFunc() is a save/export function of the current db.) 

class TempStore
{
public:
    TempStore() {/* delete some stuff from a db and store this in memory*/}
    ~TempStore() {/* write this stuff back into the db*/}
};

void someFunc(bool testCondition)
{
    TempStore tempObj = TempStore();
    // some code
    if (testCondition)
        return; //early return
    // some more code
}

Upvotes: 3

Views: 1162

Answers (3)

Nikita
Nikita

Reputation: 960

Yes, destructor will be called. Every object, created on stack will be correctly destroyed if you early return. If exception is thrown, destructor will be called after program execution arrived to the catch block.

Upvotes: 2

Mike Seymour
Mike Seymour

Reputation: 254411

The destructor of an automatic object will be called when the program leaves the object's scope. This includes returning from the function (early or otherwise), and leaving via an exception - as long as the exception is handled. In the case of an exception, it's called during stack unwinding before the exception is handled.

It might not be called in some cases, including:

  • leaving via a call to longjmp; this gives undefined behaviour;
  • leaving via an exception that's not handled; it's unspecified whether the stack is unwound.
  • terminating the program (e.g. calling exit, or raising a signal that causes termination).

Upvotes: 6

Mankarse
Mankarse

Reputation: 40613

The destructor will be called unless the program blows up due to a seg fault or a power outage or whatever. Simply returning early from a function or throwing an exception is not enough to stop the destructor running.

This design is a bit flawed though, since writing to a database is an operation that could fail, and throwing an exception from a destructor is a pretty bad idea.

Upvotes: 2

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