C++ bool vs void* casts on the same object

The code below prints 'operator bool' when used in the if statement and operator void* when it needs a bool for function call?

Why isn't it using operator bool for the function call too? and how to make it use it in both cases?

#include <iostream>

class A
{
public:
    explicit operator bool() const
    {
        std::cout << "operator bool" << std::endl;
        return true;
    }

    operator void*() const
    {
        std::cout << "operator void*" << std::endl;
        return 0;
    }
};

void f(bool valid)
{
    std::cout << "f called " << valid << std::endl;
}

int main(int argc, char *argv[])
{
    A a;

    if(a)
        std::cout << "if a" << std::endl;

    f(a);

    return 0;
}