暂存

struct foo
{
    operator int*() const
    {
        return 0;
    }
    foo operator+ (int) const
    {
        return *this;
    }
};

int main()
{
    foo() + 0u;

    return 0;
}
可以编译通过

struct foo
{
    operator int*() const
    {
        return 0;
    }
    foo operator+ (unsigned) const
    {
        return *this;
    }
};

int main()
{
    foo() + 0;

    return 0;
}
在VC++2008中报错
error C2666: 2 overloads have similar conversions
could be 'foo foo::operator +(unsigned int) const'
or       'built-in C++ operator+(int *, int)'

在GCC4.5中有警告
warning: ISO C++ says that these are ambiguous, even though the worst conversion for the first is better than the worst conversion for the second:
candidate 1: foo foo::operator+(unsigned int) const
candidate 2: operator+(int*, int)