Is it safe to make a const reference member to a temporary variable?

Question

I\'ve tried to code like this several times:

struct Foo
{
    double const& f;
    Foo(double const& fx) : f(fx)
    {
        printf(\"%f %f\\n\", f         


        

Answer 1

But it doesn't crash at all. I've also used valgrind to test the program but no error or warning occured.

Ah, the joy of debugging undefined behaviour. It's possible that the compiler compiles invalid code to something where tools can no longer detect that it's invalid, and that's what happens here.

From the OS perspective, and from valgrind's perspective, the memory that f references is still valid, therefore it doesn't crash, and valgrind doesn't report anything wrong. The fact that you see an output value of 0 means the compiler has, in your case, re-used the memory that was formerly used for the temporary object to store some other unrelated value.

It should be clear that attempts to access that unrelated value through a reference to an already-deleted object are invalid.