bug1557.cpp

1     #include <stdio.h>
2
3     class A { public: int a, b; };
4     class B
5         {
6       public:
7         const A a;
8         B() :a() { }
9         };
10
11    int main()
12        {
13        B b;
14        printf( "%d %d\n", b.a.a, b.a.b );
15        return 0;
16        }

Our programmer was having a few difficulties so he reduced his program down to the above simple example and was amazed to find that it did not print zeros. What's going on?

bug1557.cpp lint Output

--- Module:   bug1557.cpp
           _
    B() :a() { }
bug1557.cpp(8) : Warning 1557: const member 'B::a' is not initialized
bug1557.cpp(8) : Warning 1401: member 'B::a' (line 8) not initialized by constructor

Reference Manual Explanation

1557  const member 'Symbol' is not initialized  -- A class member typed const class
      (or struct or union) is mentioned in a constructor initializer list. But the
      class (or struct or union) referenced has no constructor and hence the member
      is not initialized.  See also message  1769.