Occasionally...
When the object is referenced via a pointer or a reference, a call to a virtual function cannot be inlined, since the call must be resolved dynamically. Reason: the compiler can't know which actual code to call until run-time (i.e., dynamically), since the code may be from a derived class that was created after the caller was compiled.
Therefore the only time an inline virtual call can be inlined is when the compiler knows the "exact class" of the object which is the target of the virtual function call. This can happen only when the compiler has an actual object rather than a pointer or reference to an object. I.e., either with a local object, a global/static object, or a fully contained object inside a composite.
虚函数可以重载为内联。虚函数和内联函数是两个不同的概念,它们可以单独使用,也可以结合使用。
虚函数(virtual function)主要用于实现多态性,允许派生类重写基类中的函数。当使用基类的指针或引用调用一个虚函数时,会根据实际对象的类型来决定调用哪个版本的函数。
内联函数(inline function)则是一种优化手段,用于减少函数调用的开销。内联函数会在编译时将其代码直接插入到调用点,从而避免函数调用的开销。但需要注意的是,内联函数的定义对编译器来说只是一个建议,编译器可以选择忽略这个建议,不将函数内联。
因此,虚函数可以声明为内联的,但这并不意味着它一定会被内联。内联函数的声明只是一个建议,而虚函数的调用则涉及到运行时多态性。即使虚函数被声明为内联,当通过基类指针或引用调用虚函数时,多态性的行为仍然会保留,即调用的是派生类的版本。
所以正确答案是:
A 可以