- As long as you don't access/use firstgid before initializing it, there's no problem at all with that. Check if the function which is receiving a reference to it is not using it. By using it I mean calling a function on the object, using its value (which is not necessarily bad, the only problem is that you don't know what value it holds) or trying to dereference it if it were a pointer.
- Mar 07, 2018 If NULL is defined as (void.)0 in C or as nullptr in C, then it can be assigned only to a pointer type. And since MSDN cannot control how the C and C header files define NULL, it needs to work with any definition that is permitted by the corresponding standards.Which means that saying NULL implies that the underlying type is a pointer type. Therefore, you are welcome to write nullptr.
Print Nullptr
关键词 nullptr 代表指针字面量。 它是 std::nullptrt 类型的纯右值。 存在从 nullptr 到任何指针类型及任何成员指针类型的隐式转换。 同样的转换对于任何空指针常量也存在,空指针常量包括 std::nullptrt 的值,以及宏 NULL 。 示.
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In this section we will see the nullptr in C++. The nullptr denotes the pointer literals. It is a prvalue of type std::nullptr_t. It has implicit conversion property from nullptr to null pointer value of any pointer type and any pointer to member type. Let us see one program, to understand this concept.
Example
Output
So what is the problem in the above program? The NULL is typically defined as (void*)0. We are allowed to convert NULL to integral type. So the function call of my_func(NULL) is ambiguous.
If we use the nullptr in the place of NULL, we will get the result like below −
Example
Output
We can use the nullptr at all places where NULL is expected. Like the NULL, the nullptr also can be converted into any pointer type. But this is not implicitly convertible to integral type like NULL.
C++11/C++14 The nullptr and strong typed enumerations- 2020
![C++ nullptr library C++ nullptr library](/uploads/1/2/6/1/126159174/493614677.png)
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'If you're an experienced C++ programmer and are anything like me, you initiallyapproached C++11 thinking, 'Yes, yes, I get it. It's C++, only more so.' But as youlearned more, you were surprised by the scope of the changes. auto declarations,range-based for loops, lambda expressions, and rvalue references change the face ofC++, to say nothing of the new concurrency features. And then there are theidiomatic changes. 0 and typedefs are out, nullptr and alias declarations are in.Enums should now be scoped. Smart pointers are now preferable to built-in ones.Moving objects is normally better than copying them.
- Effective Modern C++ by Scott Meyers
- Effective Modern C++ by Scott Meyers
The constant 0 has had the double role of constant integer and null pointer constant. The ambiguity inherent in the double meaning of 0 was dealt with in C by the use of the preprocessor macro NULL, which commonly expands to either ((void*)0) or 0.
C++ didn't adopt the same behavior, allowing only 0 as a null pointer constant.
This interacts poorly with function overloading:
If NULL is defined as 0, which function the statement foo(NULL) will call?
Probably, it will call foo(int), which is almost certainly not what the programmer intended. In other words, there is an ambiguity.
So, C++11 corrected this by introducing a new keyword to serve as a distinguished null pointer constant (nullptr):
In C++03, enumerations are not type-safe. They are effectively integers, even when the enumeration types are distinct. This allows the comparison between two enum values of different enumeration types.
initializer_list
Uniform initialization
Type Inference (auto) and Range-based for loop
The nullptr and strongly typed enumerations
Static assertions and Constructor delegation
override and final
default and delete specifier
![Dev C++ Nullptr Dev C++ Nullptr](/uploads/1/2/6/1/126159174/833104277.png)
Lambda functions and expressions
std::array container
Rvalue and Lvalue (from C++11 Thread tutorial)
Move semantics and Rvalue Reference (from C++11 Thread tutorial)
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