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A long double (eight bytes with Visual C++, sixteen bytes with GCC) will be 8-byte aligned with Visual C++ and 16-byte aligned with GCC. Any pointer (eight bytes) will be 8-byte aligned. Some data types are dependent on the implementation. Here is a structure with members of various types, totaling 8 bytes before compilation:
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.
The fact that structs in C++ are classes/objects with members that are public by default should not be of any real interest, unless you're writing code to parse C++ source. There's a clear conceptual difference between a struct and a class, and C++'s "structs" are not really structs at all. --StuartBrady 20:35, 4 March 2006 (UTC)
The One Definition Rule (ODR) is an important rule of the C++ programming language that prescribes that classes/structs and non-inline functions cannot have more than one definition in the entire program and templates and types cannot have more than one definition by translation unit.
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.
Structure and union specifiers have the same form. ] The size of a union is sufficient to contain the largest of its members. The value of at most one of the members can be stored in a union object at any time.
This article, however, focuses on differences that cause conforming C code to be ill-formed C++ code, or to be conforming/well-formed in both languages but to behave differently in C and C++. Bjarne Stroustrup , the creator of C++, has suggested [ 4 ] that the incompatibilities between C and C++ should be reduced as much as possible in order to ...
The second notable difference is that the void type is special and can never be stored in a record type, i.e. in a struct or a class in C/C++. In contrast, the unit type can be stored in records in functional programming languages, i.e. it can appear as the type of a field; the above implementation of the unit type in C++ can also be stored.