Re: problem with (use of) std::vector

SYNOPSIS
=========
I am experiencing a strange problem, which I'm sure is caused by an
oversight on my part - but despite peering over the code for a few
hours, I have been able to spot the bug. I am writing a simple generic
value container. A generic value is implemented as a discriminated union
class (B), which is nested within the container class A. Class A stores
instances of generic values in a std::vector.

The container as described, works well for fundamental data types,
however, when I attempt to store pointer types (which are managed by
class B), a memory access/violation exception is thrown).

SAMPLE CODE TO REPRODUCE ISSUE
===============================
class A
{
public:
    A(){}
    ~A(){}

    size_t addValue(const std::string& s)
    {
        m_values.push_back(B(s.c_str()));
        return m_values.size();
    }

    size_t addValue(const long l)
    {
        m_values.push_back(B(l));
        return m_values.size();
    }

private:
    class B
    {
    public:
        friend class A;

        B():m_stype(false)
        {
            m_value.l = 0;
        }

        explicit B(const long l):m_stype(false)
        {
            m_value.l = l;
        }

        explicit B(const char* s):m_stype(true)
        {
            //error checking omitted for brevity
            m_value.s = strdup(s);
        }

        ~B()
        {
            if (m_stype && m_value.s)
                free(m_value.s);
        }

        B(const B& b):m_stype(b.m_stype), m_value(b.m_value)
        {}

Can anyone spot the cause of this error?