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Questions tagged [nullptr]

The C++11 keyword for a null pointer, it can be converted to any pointer type. Also available in C23 through stddef.h. Always use this tag either in combination with the C++ or the C tag.

In C++, nullptr is a null pointer constant of type std::nullptr_t which can be implicitly converted to any pointer type. An integer constant 0 can also be converted to any pointer type but can also be deduced as an integer in other contexts, leading to ambiguities. See What exactly is nullptr?

In C ("C23" ISO 9899:202x), nullptr is similarly a null pointer constant of type nullptr_t found in stddef.h. It can get converted to a void*, bool or a pointer type.

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What exactly is nullptr?

We now have C++11 with many new features. An interesting and confusing one (at least for me) is the new nullptr. Well, no need anymore for the nasty macro NULL. int* x = nullptr; myclass* obj = nullptr; Still, I am not getting how nullptr works.…
Khaled Alshaya
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NULL vs nullptr (Why was it replaced?)

I know that in C++ 0x or NULL was replaced by nullptr in pointer-based applications. I'm just curious of the exact reason why they made this replacement? In what scenario is using nullptr over NULL beneficial when dealing with pointers?
Riptyde4
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What are the advantages of using nullptr?

This piece of code conceptually does the same thing for the three pointers (safe pointer initialization): int* p1 = nullptr; int* p2 = NULL; int* p3 = 0; And so, what are the advantages of assigning pointers nullptr over assigning them the values…
Mark Garcia
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C++11 When clearing shared_ptr, should I use reset or set to nullptr?

I have a question about C++11 best practices. When clearing a shared_ptr, should I use the reset() function with no parameter, or should I set the shared_ptr to nullptr? For example: std::shared_ptr foo(new…
user1930581
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Why not call nullptr NULL?

In C++11 the nullptr keyword was added as a more type safe null pointer constant, since the previous common definition of NULL as 0 has some problems. Why did the standards committee choose not to call the new null pointer constant NULL, or declare…
user253751
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Can nullptr be emulated in gcc?

I saw that nullptr was implemented in Visual Studio 2010. I like the concept and want to start using it as soon as possible; however GCC does not support it yet. My code needs to run on both (but doesn't have to compile with other compilers). Is…
nuzz
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Why can't you take the address of nullptr?

In the C++11 standard, I don't understand the reason why taking the address of nullptr is disallowed whereas one is allowed to take the address of their own std::nullptr_t instances. Aside from the fact that nullptr is a reserved keyword, is there…
monkey0506
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Can the NULL macro actually be a nullptr?

According to the draft of the standard N4713 (7.11/1): A null pointer constant is an integer literal (5.13.2) with value zero or a prvalue of type std::nullptr_t. and 21.2.3/2: The macro NULL is an implementation-defined null pointer…
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Is it safe to #define NULL nullptr?

I have seen below macro in many topmost header files: #define NULL 0 // C++03 In all over the code, NULL and 0 are used interchangeably. If I change it to. #define NULL nullptr // C++11 Will it cause any bad side effect ? I can think of the only…
iammilind
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Why is C++'s NULL typically an integer literal rather than a pointer like in C?

I've been writing C++ for many years, using nullptr for null pointers. I also know C, whence NULL originates, and remember that it's the constant for a null pointer, with type void *. For reasons, I've had to use NULL in my C++ code for something.…
einpoklum
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Pure virtual functions in C++11

In C++98, the null pointer was represented by the literal 0 (or in fact any constant expression whose value was zero). In C++11, we prefer nullptr instead. But this doesn't work for pure virtual functions: struct X { virtual void foo() =…
fredoverflow
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Why isn't 'nullptr' in the 'std' namespace?

It seems that nullptr is declared in the default global namespace. Wouldn't it make sense for it to be in the std namespace?
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What are the uses of the type `std::nullptr_t`?

I learned that nullptr, in addition to being convertible to any pointer type (but not to any integral type) also has its own type std::nullptr_t. So it is possible to have a method overload that accepts std::nullptr_t. Exactly why is such an…
Hindol
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Why does const auto &p{nullptr} work while auto *p{nullptr} doesn't in C++17?

This definition works: const auto &b{nullptr}; while this fails: auto *b{nullptr}; I have tried to compile this in Visual C++, GCC, and Clang. They all complain "cannot deduce type". In the second case, shouldn't b be deduced to have some type…
felix
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