A gcc compilation error (concerning copy c'tors) which seems odd (at least to me)
testref.cpp: In function ‘int main()’:
testref.cpp:10: error: ‘A::A(const A&)’ is private
testref.cpp:20: error: within this context

#include <cstdio>

class A {
public:
    A() { i=0; printf("A ctorn"); }
    ~A() { printf("A dtorn"); }

private:
    A(const A& other) { i=other.i; printf("A COPY CTORn"); }
    A& operator=(const A& other) { i=other.i; printf("A COPY operatorn"); return *this; }
private:
    int i;
};

void f(const A &aref) {
    printf("dummyn");
}

int main() {
    f(A());
    return 0;
}

test.cpp:20:7: warning: C++98 requires an accessible copy constructor for class
              'A' when binding a reference to a temporary; was private