Constructors for Structs in C++

I came across the following practice question and answer while studying C++ and I do not understand it.

Given:

class B {};

struct A {
   A( B b );
};

Call the function void test( A a, int* b=0); with the two corresponding variables B b, int i;

The answer is test( b, &i );

My question is, how is it enough to pass the necessary parameter of the constructor and not actually call it? In my mind, the answer should have been:

test( A(b), &i);

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Link to original article：https://stackoverflow.com/questions/39864867/constructors-for-structs-in-c