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This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 119a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2025-12-20

2176. Destroying the returned object when a destructor throws

[Adopted at the February, 2016 meeting.]

Consider the following example:

  #include <stdio.h>  struct X {    X() { puts("X()"); }    X(const X&) { puts("X(const X&)"); }    ~X() { puts("~X()"); }  };  struct Y { ~Y() noexcept(false) { throw 0; } };  X f() {    try {      Y y;      return {};    } catch (...) {    }    return {};  }  int main() {    f();  }

Current implementations printX() twice but~X() only once. That is obviously wrong, but it isnot clear that the current wording covers this case.

Proposed resolution (February, 2016):

Change 14.3 [except.ctor] paragraph 2 as follows:

The destructor is invoked for each automatic object ofclass type constructed, but not yet destroyed,since the try block was entered.If an exception isthrown during the destruction of temporaries or localvariables for areturn statement(8.8.4 [stmt.return]), the destructor for thereturned object (if any) is also invoked. Theautomatic objects are destroyed in the reverseorder of the completion of their construction.[Example:

  struct A { };  struct Y { ~Y() noexcept(false) { throw 0; } };  A f() {    try {      A a;      Y y;      A b;      return {};   // #1    } catch (...) {    }    return {};     // #2  }

At#1, the returned object of typeAis constructed. Then, the local variableb isdestroyed (8.8 [stmt.jump]). Next, the local variabley is destroyed, causing stack unwinding, resulting inthe destruction of the returned object, followed by thedestruction of the local variablea. Finally, thereturned object is constructed again at#2.—end example]