https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85043
Bug ID: 85043
Summary: -Wuseless-cast false positive for temporary objects
Product: gcc
Version: 7.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: b...@michael-lossin.de
Target Milestone: ---
> cat x.cc
#include <iostream>
struct A
{
int value = 42;
A & inc() { ++value; return *this; }
};
int main()
{
{
A a;
std::cout << A(a).inc().value << ", ";
std::cout << a.value << "\n";
}
{
A a;
std::cout << a.inc().value << ", ";
std::cout << a.value << "\n";
}
}
> g++ -Wuseless-cast -o x x.cc
x.cc: In function 'int main()':
x.cc:13:21: warning: useless cast to type 'A' [-Wuseless-cast]
std::cout << A(a).inc().value << ", ";
^
> ./x
43, 42
43, 43
Here, A(a) is not a cast but creates a temporary object which in turn is
modified. Removing the "useless cast" would alter the original object, so the
warning should not be shown in this case.
