C ++分配标准？

Question

Let's assume I have a class Foo, and a function Bar

void Bar(void)
{
Foo a();
}

Does that mean that a will necessarely be NOT allocated in the main memory ? Or does this depend on compilers so the compiler may allocate memory and result in the same thing as if we wrote Foo* a=new Foo

Answer 1

Foo a(); is a function declaration. It should be Foo a ; And a is in the memory of stack.

Answer 2

The term you're looking for is an automatic variable . This means that the object contained in that variable is guaranteed to be destroyed at the end of the scope automatically .

When you use new , the object is destroyed only when you delete it explicitly (or by explicitly using a mechanism that takes care of destroying it, like smart pointers). In other words, the lifetime is manually managed.

Of course, automatic lifetime semantics are not the same as manual semantics under any circumstance. That being said, the storage location (stack, heap, registers, or something else) in both cases is irrelevant.

Answer 3

Technically, if a fits in a register, it could end up using "no memory" at all. Otherwise, it will be allocated on the stack, in what I would call "main memory", same kind of memory as with Foo *a = new Foo; , but a different portion [ new uses heap memory, the stack is not same as heap, but same KIND of memory].

Of course, if the class Foo contains a constructor, it could in itself call new and all manner of other functions that may or may not alter the usage of memory...