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[Bug c++/62172] New: Operand to a throw expression is moved when it should be copied
- From: "tsimpson at ubuntu dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Mon, 18 Aug 2014 15:33:54 +0000
- Subject: [Bug c++/62172] New: Operand to a throw expression is moved when it should be copied
- Auto-submitted: auto-generated
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62172
Bug ID: 62172
Summary: Operand to a throw expression is moved when it should
be copied
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: tsimpson at ubuntu dot com
Created attachment 33352
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33352&action=edit
test case
With a throw expression whos operand is an lvalue, which is declared outside
the try block, will move from the expression instead of copy.
The relavent part of the standard is 15.1 [except.throw].
The C++11 standard *could* be interpreded to allow the move when reading the
last sentence of 15.1/3
"...Except for these restrictions and the restrictions on type matching
mentioned in 15.3, the operand of throw is treated exactly as a function
argument in a call (5.2.2) or the operand of a return statement."
Specifically, if the operand of the throw expression was treated exactly the
same as an operand to a return statement then it would become an xvalue and the
move would be allowed.
The wording of that clause changed in C++14, so this is no longer the case. And
I don't think it was the intent to allow that in C++11 either.
Example output with g++ http://rextester.com/USFXJ5678
Exmaple output with clang++ http://rextester.com/EARQ18237