使用C ++的数据结构

Question

if we are having are having an array of pointer ie

struct node*ptr[];

and if we want to initialize its value of first index ( ptr[0] ) by null then how can we do that?

Answer 1

如果要初始化ptr[0] ，则必须为数组指定固定大小（例如struct node *ptr[1] ）或分配内存（ struct node *ptr[] = new node *;

Answer 2

You can also do something like this:

struct node* ptr [10] = { 0 };

which initializes all pointers to null.

Answer 3

struct node*ptr[];

does not really declare a valid array, typically you need to specify a size or initialize in such a way that the compiler can determine the size at compile time . Also, you don't need the struct in C++, it's a throwback to C!

for example, valid options are:

node* ptr[10] = { 0 }; // declares an array of 10 pointers all NULL

or, you can initialize without the size and the compiler figures it out..

node* ptr[] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }; // 10 node* pointers all NULL

Answer 4

If you are trying to use a statically sized array, use std::array . If you using an array that can be resized, use std::vector :

#include <array>
#include <vector>

struct Node {};
typedef std::vector<Node*> DynamicNodeArray;
typedef std::array<Node*, 10> StaticNodeArray;

int main()
{
    DynamicNodeArray dyn_array(10);     // initialize the array to size 10
    dyn_array[0] = NULL;                // initialize the first element to NULL

    StaticNodeArray static_array;       // declare a statically sized array
    static_array[0] = NULL;             // initialize the first element to NULL
}

Answer 5

Use ptr[0] = NULL; (assuming you have declared ptr correctly ie something like ptr[10] ) Is that what you are asking?

Answer 6

This is based on C

  struct node*ptr[];

This means ptr can hold address of node, it is a array of node type pointer. just like

struct node *start = (struct node*)malloc(sizeof(struct node));

As you know array size is fixed, we have to give array size before it's use, so first of all you have to give array size.

Here malloc(sizeof(struct node)) will return void type pointer, that by we have to do type casting.