Lifetime of temporaries bound to references in C++11

Newsgroup: comp.lang.c++

Subject: Lifetime of temporaries bound to references in C++11

From: Michael Mehlich <michael@...>

Date: Fri, 05 Jul 2013 18:01:46 -0500



I noticed an unexpected order of destructor calls for temporaries

bound to references wrt the lifetime of the enclosing object

when experimenting with C++11 using gcc 4.9.0.



In particular, the program included below produced the output

done

~C

~B

~D

which is counter to my expectation of

done

~D

~C

~B

Looking at the C++11 standard, 12.2p5 clearly requires

~C to be called before ~B (reverse order of completion of

construction). However, the ordering of object vs. temporary

is specified wrt. the moment the object/temporary is created.

Searching the standard, it isn't clear to me when an object

or temporary is actually considered as "created", in particular

wrt. the evaluation of the constructor.



What (and where) does the standard actually say about the relative

lifetimes/ the order of destruction in this scenario?



--

Michael





extern "C" int printf(const char *, ...);



struct B {

~B() { printf("%s\n",__func__); }

int x;

int y;

};



struct C {

~C() { printf("%s\n",__func__); }

int x;

const B &b;

int y;

};



struct D {

~D() { printf("%s\n",__func__); }

int x;

const C &c;

int y;

};



int main() {

D d = { 1, { 2, { 3, 4 }, 5 } , 6 };

printf("done\n");

}



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