c ++指向结构数组的指针

Question

Can someone please explain to me why this doesn't work?

struct person {
  string name;
  int age;
};

// in function
person friends[NUM_OF_FRIENDS];
friends[0].name = "bob";
friends[1].name = "bill";
friends[2].name = "liz";
friends[3].name = "frank";
friends[4].name = "carl";
friends[0].age = 20;
friends[1].age = 30;
friends[2].age = 32;
friends[3].age = 10;
friends[4].age = 85;

// array of pointers

person (*friends_ptrs)[NUM_OF_FRIENDS] = &friends;

cout << friends_ptrs[0]->name << endl;

cout << friends_ptrs[1]->name << endl;

"bob" is printed fine, but "bill" causes an error. How can "bob" print at all while "bill" is not found?

I realize that I can just do this:

person *friends_ptrs = friends;

But then I'm not using the arrow notation, and it defeats the purpose of this exercise.

So how can I access the friends[] struct, using a pointer with arrow notation?

Answer 1

You've created a pointer to an array, not an array of pointers.

So, this will work:

cout << (*friends_ptrs)[1].name << endl;

If you want an array of pointers, write:

person* friends_ptrs[NUM_OF_FRIENDS];

friends_ptrs[0] = &friends[0];
friends_ptrs[1] = &friends[1];
// ...

Answer 2

I don't understand what exactly you are trying to do. If you want to get an array of pointers from your array of structs, you will need to make a loop. It would look like this (i did not try it)

person * friends_ptrs[NUM_OF_FRIENDS];
for (int i = 0; i < NUM_OF_FRIENDS; i++)
    friends_ptrs[i] = friends + i;

Answer 3

first thing that you must know is that name of array is address of first node of array,so when you must change this line :

person (*friends_ptrs)[NUM_OF_FRIENDS] = &friends;

to

person* friends_ptrs = friends;

tow,in above line you ought not create an array of pointers.

Answer 4

friends is a pointer to the first element in array. Using pointer arithmetic you can use the arrow notation in following way:

cout << friends->name;
cout << (friends++)->name; //Incrementing it will give you the pointer to second one.