When are temporaries created as part of a function call destroyed?
- by Michael Mrozek
Is a temporary created as part of an argument to a function call guaranteed to stay around until the called function ends, even if the temporary isn't passed directly to the function?
There's virtually no chance that was coherent, so here's an example:
class A {
public:
A(int x) : x(x) {printf("Constructed A(%d)\n", x);}
~A() {printf("Destroyed A\n");}
int x;
int* y() {return &x;}
};
void foo(int* bar) {
printf("foo(): %d\n", *bar);
}
int main(int argc, char** argv) {
foo(A(4).y());
}
If A(4) were passed directly to foo it would definitely not be destroyed until after the foo call ended, but instead I'm calling a method on the temporary and losing any reference to it. I would instinctively think the temporary A would be destroyed before foo even starts, but testing with GCC 4.3.4 shows it isn't; the output is:
Constructed A(4)
foo(): 4
Destroyed A
The question is, is GCC's behavior guaranteed by the spec? Or is a compiler allowed to destroy the temporary A before the call to foo, invaliding the pointer to its member I'm using?
