Unable to print the value of nullptr on screen

Question

I was reading about nullptr and doing workout on g++ and also on VS2010.

When I did

#include 
using namespace std;

aut         


        

Answer 1

I ran into this problem while I was writing some type-parameterized test code (using templates). I needed to print a value of type T, where nullptr_t was a valid type for T. I came up with a solution where the value to be printed was wrapped inside a printable template function. This function then makes use of template specialization to provide the desired behavior when a nullptr_t is used.

#include 
#include 

template  struct Printable
{
    Printable(const T& val) : val(val) {}
    void print(std::ostream& out) const {out << val;}
    const T& val;
};

template <> struct Printable
{
    Printable(nullptr_t) {}
    void print(std::ostream& out) const {out << "null";}
};

template 
Printable printable(const T& value) {return Printable(value);}

template 
std::ostream& operator<<(std::ostream& out, const Printable& p)
{
    p.print(out);
    return out;
}

int main() {
    std::cout << printable(42) << " " << printable(nullptr) << "\n";
    return 0;
}

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