Question

例:

class A{

int b;
A *a1;
A *a2;

A(int c):b(c), a1(c), a2(c)  {}

}

I thought this was the way, but it doesn t compile. Is there a way to do this, or is it necessary to always use dynamic allocation? thanks

Answer 1

你可以简单地把要点推向无效。

class A{

   int b;
   A *a1;
   A *a2;

   A(int c):b(c), a1(NULL), a2(NULL)  {}

}

(注,如果它抱怨未界定的NCL,#include <cstddef>)

Or not initialize them at all.

class A{

   int b;
   A *a1;
   A *a2;

   A(int c):b(c)  {}

}

Answer 2

It s not clear what you re trying to do, but you certainly can do it:

class A{

int b;
A *a1;
A *a2;

A(int c, A* pa1, A* pa2):b(c), a1(pa1), a2(pa2)  {}

}

你可以这样说:

A m1(1, NULL, NULL);
A m2(2, NULL, NULL);
if(something())
{
  A m3(3, &m1, &m2);
  // do stuff with m3
}

值得小心。 m1或m2 在m3之前,m3将留有点人,标明任意停车场。

Answer 3

如果您不想将点数推到nullptr(NUL或0 pre-C++11)上,那么:

class A {
    A(int c) : b(c), a1(), b1() { }

    int b;
    A* a1, *a2;
};

then either the object you make the pointer point to has to exist in some outer scope so that it will live at least as long as the object that contains the pointer, or you have to use new.

You could accept an A* to set the pointers to:

class A {
    A(int c, A* aptr) : b(c), a1(aptr), a2(aptr) { }

    ... 
};

(因为这样将形成一个<代码>) A a demand for an A, an possible conditions to hold. 你们可以再造一个接受参考的建筑商。

In your example, you are trying to use an int to initialise a pointer which won t work. Also, if you create an object in your example (via new or whatever), you will run out of memory because each A you allocate will allocate two more As and that cycle will continue until you run out of memory.

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