What are the differences between struct and class in C++?

c++ oop class struct c++-faq
palm3D picture palm3D · Sep 18, 2008 · Viewed 344.4k times · Source

This question was already asked in the context of C#/.Net.

Now I'd like to learn the differences between a struct and a class in C++. Please discuss the technical differences as well as reasons for choosing one or the other in OO design.

I'll start with an obvious difference:

  • If you don't specify public: or private:, members of a struct are public by default; members of a class are private by default.

I'm sure there are other differences to be found in the obscure corners of the C++ specification.

Answer

Assaf Lavie picture Assaf Lavie · Jun 16, 2009

You forget the tricky 2nd difference between classes and structs.

Quoth the standard (§11.2.2 in C++98 through C++11):

In absence of an access-specifier for a base class, public is assumed when the derived class is declared struct and private is assumed when the class is declared class.

And just for completeness' sake, the more widely known difference between class and struct is defined in (11.2):

Member of a class defined with the keyword class are private by default. Members of a class defined with the keywords struct or union are public by default.

Additional difference: the keyword class can be used to declare template parameters, while the struct keyword cannot be so used.

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