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# nullptr
Designates a null pointer constant of type `std::nullptr_t`, which is convertible to any raw pointer type.  Although you can use the keyword `nullptr` without including any headers, if your code uses the type `std::nullptr_t`, then you must define it by including the header `<cstddef>`.  
  
> [!NOTE]
>  The `nullptr` keyword is also defined in C++/CLI for managed code applications and is not interchangeable with the ISO Standard C++ keyword. If your code might be compiled by using the [/clr](../build/reference/clr-common-language-runtime-compilation.md) compiler option, which targets managed code, then use `__nullptr` in any line of code where you must guarantee that the compiler uses the native C++ interpretation. For more information, see [nullptr](../windows/nullptr-cpp-component-extensions.md).  
  
## Remarks  
 Avoid using `NULL` or zero (`0`) as a null pointer constant; `nullptr` is less vulnerable to misuse and works better in most situations.  For example, given `func(std::pair<const char *, double>)`, then calling `func(std::make_pair(NULL, 3.14))` causes a compiler error.  The macro NULL expands to `0`, so that the call `std::make_pair(0, 3.14)` returns `std::pair<int, double>`, which is not convertible to func()'s `std::pair<const char *, double>` parameter type.  Calling `func(std::make_pair(nullptr, 3.14))` successfully compiles because `std::make_pair(nullptr, 3.14)` returns `std::pair<std::nullptr_t, double>`, which is convertible to `std::pair<const char *, double>`.  
  
## See Also  
 [Keywords](../cpp/keywords-cpp.md)   
 [nullptr](../windows/nullptr-cpp-component-extensions.md)


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