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The compiled size of the structure is now 12 bytes. The last member is padded with the number of bytes required so that the total size of the structure should be a multiple of the largest alignment of any structure member (alignof(int) in this case, which = 4 on linux-32bit/gcc) [citation needed].
In the C programming language, struct is the keyword used to define a composite, a.k.a. record, data type – a named set of values that occupy a block of memory. It allows for the different values to be accessed via a single identifier, often a pointer. A struct can contain other data types so is used for mixed-data-type records.
In C and C++ short, long, and long long types are required to be at least 16, 32, and 64 bits wide, respectively, but can be more. The int type is required to be at least as wide as short and at most as wide as long , and is typically the width of the word size on the processor of the machine (i.e. on a 32-bit machine it is often 32 bits wide ...
A class in C++ is a user-defined type or data structure declared with any of the keywords class, struct or union (the first two are collectively referred to as non-union classes) that has data and functions (also called member variables and member functions) as its members whose access is governed by the three access specifiers private, protected or public.
Before C++11, the values of variables could be used in constant expressions only if the variables are declared const, have an initializer which is a constant expression, and are of integral or enumeration type. C++11 removes the restriction that the variables must be of integral or enumeration type if they are defined with the constexpr keyword:
In C++, classes and structs can be forward-declared like this: class MyClass ; struct MyStruct ; In C++, classes can be forward-declared if you only need to use the pointer-to-that-class type (since all object pointers are the same size, and this is what the compiler cares about).
The sizeof operator on such a struct gives the size of the structure as if the flexible array member were empty. This may include padding added to accommodate the flexible member; the compiler is also free to re-use such padding as part of the array itself.
The A::max_size() member function returns the largest number of objects of type T that could be expected to be successfully allocated by an invocation of A::allocate; the value returned is typically A::size_type(-1) / sizeof(T). [14] Also, the A::address member function returns an A::pointer denoting the address of an object, given an A::reference.