This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 117a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2025-04-13
2176. Destroying the returned object when a destructor throwsSection: 7.6.1.3 [expr.call] Status: CD4 Submitter: Richard Smith Date: 2015-09-28[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 print X() twice but ~X() only once. That is obviously wrong, but it is not 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 of class type constructed , but not yet destroyed, since the try block was entered. If an exception is thrown during the destruction of temporaries or local variables for a return statement (8.7.4 [stmt.return]), the destructor for the returned object (if any) is also invoked. The automatic objects are destroyed in the reverse order 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 type A is constructed. Then, the local variable b is destroyed (8.7 [stmt.jump]). Next, the local variable y is destroyed, causing stack unwinding, resulting in the destruction of the returned object, followed by the destruction of the local variable a. Finally, the returned object is constructed again at #2. —end example]
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