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#include <iostream>
#include <memory>
 
// #define USE_CXX11_NULLPTR
 
#ifndef USE_CXX11_NULLPTR
////////////////////////////////////////////
// To avoid errors in latest GCC which is used by IDEOne.
// In my case I use GCC 4.5.3 where it supports some features of C++11, but not nullptr.
#define nullptr nullptr__
#define nullptr_t nullptr_t__
////////////////////////////////////////////
 
namespace std {
 
class nullptr_t {
public:
 
nullptr_t() { }
template <typename T> nullptr_t(const T&) { }
template <class T> nullptr_t(const T*) { }
template <class T> nullptr_t(T*) { }
template <typename T, typename  U> nullptr_t(const typename T::U*) { }
 
template<typename T> operator T*() { return 0;}
template<typename T1, typename T2> operator T1 T2::*() { return 0; }
 
operator int() const { return 0; }
operator unsigned() const { return 0; }
operator bool() const { return false; }
bool operator == (unsigned i) const { return i == 0; }
bool operator != (unsigned i) const { return i != 0; }
bool operator !() const { return true; }
 
} nullptr = {};
 
}
 
using std::nullptr;
 
#endif //USE_CXX11_NULLPTR
 
template<typename T> struct DummyContainer {
	DummyContainer(T* ptr)
		: m_ptr(ptr) { }
 
	DummyContainer(std::nullptr_t)
		: m_ptr(0) { }
 
	T& operator = (std::nullptr_t)  { return *m_ptr; }
 
	private: T* m_ptr;
};
 
int main(int argc, char** argv)
{
	const char* case1 = nullptr; // working
	// I think for below case std::unique_ptr has to be modified to take std::nullptr_t during construction & operator =
	std::unique_ptr<char> case2 =  nullptr; // not working. 
	DummyContainer<char> case3 = nullptr; // working
	case3 = nullptr; //working
	unsigned* case4 = argc > 1 ? nullptr : nullptr; //works
	unsigned* case5 = argc > 2 ? (unsigned*)0 : nullptr; //not working. (It is the major issue as of now)
 
	return 0;
}

prog.cpp: In function ‘int main(int, char**)’:
prog.cpp:10:17: error: conversion from ‘std::nullptr_t__’ to non-scalar type ‘std::unique_ptr<char>’ requested
 #define nullptr nullptr__
                 ^
prog.cpp:59:33: note: in expansion of macro ‘nullptr’
  std::unique_ptr<char> case2 =  nullptr; // not working. 
                                 ^
prog.cpp:10:17: error: operands to ?: have different types ‘unsigned int*’ and ‘std::nullptr_t__’
 #define nullptr nullptr__
                 ^
prog.cpp:63:46: note: in expansion of macro ‘nullptr’
  unsigned* case5 = argc > 2 ? (unsigned*)0 : nullptr; //not working. (It is the major issue as of now)
                                              ^
prog.cpp:57:14: warning: unused variable ‘case1’ [-Wunused-variable]
  const char* case1 = nullptr; // working
              ^
prog.cpp:62:12: warning: unused variable ‘case4’ [-Wunused-variable]
  unsigned* case4 = argc > 1 ? nullptr : nullptr; //works
            ^
prog.cpp:63:12: warning: unused variable ‘case5’ [-Wunused-variable]
  unsigned* case5 = argc > 2 ? (unsigned*)0 : nullptr; //not working. (It is the major issue as of now)
            ^

Standard output is empty