When are temporaries created as part of a function call destroyed?

Question

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 th

Answer 1

§12.2/3: "Temporary objects are destroyed as the last step in evaluating the full-expression (1.9) that (lexically) contains the point where they were created."

IOW, you're safe -- the A object must not be destroyed until after foo returns.

Answer 2

Temporary objects exist up until the end of the full expression in which they are created.

In your example, the A object created by A(4) will exist at least until the expression ends just after the return from the call to foo().

This behavior is guaranteed by the language standard:

Temporary objects are destroyed as the last step in evaluating the full-expression (1.9) that (lexically) contains the point where they were created. This is true even if that evaluation ends in throwing an exception (C++03 §12.2/3).

The lifetime of the temporary may be extended by binding a reference to it (in which case its lifetime is extended until the end of the lifetime of the reference), or by using it as an initializer in a constructor's initializer list (in which case its lifetime is extended until the object being constructed is fully constructed).

Answer 3

The lifetime of your temp object A(4) will last long enough to call y()

The memory pointed to in the return of y() is not reliable, depending on threading and allocations it may be reallocated and the value changed before the call to foo() makes use of it.

Answer 4

The temporary lasts until the end of the expression it is part of - which in this case is a function call.