Java-like annotations in C++

Question

Is there something like Java's annotations in C++ ?

For example, the @Override annotation marks a function that it overrides another function, and if it wouldn't, it would give an error at compile time.

I am looking for something like this in C++.

Answer 1

C++11 provides support for generalized attributes , which can be seen as superset of Java annotations, as they can be applied not just to variables/functions, but also to statements, for example. But C++11 defines only syntax for generalized attributes, not means for user to define them.

This article gives good overview of generalized attributes : http://www.codesynthesis.com/~boris/blog/2012/04/18/cxx11-generalized-attributes/

GCC supports this feature from version 4.8, according to: http://gcc.gnu.org/projects/cxx0x.html

To implement support for user-defined attributes, compiler plugins are promising, especially based on high-level language integration, like https://fedorahosted.org/gcc-python-plugin/

Answer 2

C++0x将具有此功能，您可以在其中明确指定成员函数是否旨在覆盖基类的函数，使用编译器生成的默认实现等等。

Answer 3

There is C++0x, which has the override 'annotation'. Or, if you wanted to achieve more of the Java "interface" like-code that errors if you don't implement methods, you could use an abstract class:

    class Base {
public:
    virtual void foo() = 0;
};

class Extended : public Base {
public:

    void foo2() {
        cout << "hi" << endl;
};

int main() {
    Extended e;
    e.foo();
}

This will result in a compiler error if you don't override foo in the base class. The issue, however, is that the base class can't have it's own implementation.

Answer 4

There's nothing in the language for this. The best you could hope for is a compiler-specific option. I'd start by checking the documentation for "pragma" for your compiler.

Answer 5

I'm not sure what JAVA provides in general, but for the specific functionality you mentioned, C++ has the override keyword:

class Derived : public Base {
    void foo() override { ... }
};

You'll get a helpful compiler error message if Base doesn't have a corresponding virtual void foo() .

Another functionally-similar keyword is final , which can be used to say that the function is an override that can't be further overridden in further-derived classes. (The same keyword can be used to say a class can't be derived from).