https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97288
Bug ID: 97288
Summary: Assignment sequence before order - evaluating
reference to value of right side not in order
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: kirshamir at gmail dot com
Target Milestone: ---
Following code results with different result in gcc and clang, seems that gcc
get wrong the sequence before:
class Number {
int num = 0;
public:
Number(int n): num(n) {
std::cout << "in ctor of Number for: " << num << std::endl;
}
// Number(const Number& n): num(n.num) {
// std::cout << "in copy of Number for: " << num << std::endl;
// }
Number& operator+=(int i) {
std::cout << "in +=(int) for *this = " << num << " and int = " << i <<
std::endl;
num += i;
return *this;
}
Number& operator+=(Number n) {
std::cout << "in +=(Number) for *this = " << num << " and Number = " <<
n << std::endl;
num += n.num;
return *this;
}
operator int() const {
return num;
}
};
int main() {
Number a {5};
(a += 1) += a;
std::cout << a << std::endl;
}
Code: https://godbolt.org/z/1P63z7
Based on stackoverflow:
https://stackoverflow.com/questions/64195482/chained-compound-assignments-with-c17-sequencing-are-still-undefined-behaviour
