about order of evaluation using shared pointers

Question

I have a doubt about the order of evaluation in a if-clause when using shared pointers.

Suppose I have the following

struct MyClass {
   bool canUse(){ return false; } // dummmy value
}

std::shared_ptr<MyClass> myclass_ptr_;

/// other code..

if(myclass_ptr_ && myclass_ptr_->canUse()) {
   // do something
}

Do you know if in that case C++ always guarantees that myclass_ptr_ is evaluated before myclass_ptr_->canUse() ?

If it is not always the case and myclass_ptr_ might come after for some reason and it is not initialised I am risking to surely crash the app.

When I run this app it seems working fine, but I just want to confirm with someone to avoid nasty surprises in a release.

The Left operand of `&&` is always evaluated first. if `false`, the Right operand is not evaluated. Unless if you are using a user-defined overload of `&&` — WhiZTiM, Feb 17 '17 at 11:09

score 3 · Accepted Answer · edited May 23 '17 at 12:09

3

Do you know if in that case C++ always guarantees that myclass_ptr_ is evaluated before myclass_ptr_->canUse() ?

Yes. This case doesn't fall under order of evaluation but short circuiting rule for &&.

From foot note on this page.

^{Builtin operators && and || perform short-circuit evaluation (do
not evaluate the second operand if the result is known after
evaluating the first), but overloaded operators behave like regular
function calls and always evaluate both operands}

Also read Why there is no circuiting when these operators are overloaded.

edited May 23 '17 at 12:09

Community

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answered Feb 17 '17 at 11:10

Mohit Jain

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@Jain: thanks a lot. The second comment is the one that probably clarifiy another doubt I had in mind. – Abruzzo Forte e Gentile Feb 17 '17 at 11:15
I am glad if this helped :) – Mohit Jain Feb 17 '17 at 11:16

about order of evaluation using shared pointers

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