C++ Struct

1. 定义

• A composite type which aggregate multiple fundamental types into a single structure
• it is a new type, defined by user

struct [type_name]
{
    member_type1 member_name 1;
    member_type2 member_name 2;
    member_type3 member_name 3;
    ...
} [object_names];

2.使用

• to access a member of a struct we use the .operator
  object_name.member_name;

• Examples

example 1

struct ComplexNumber
{
    double realPart;
    double imagPart;
};
// declare a variable of type ComplexNumber
ComplexNumber x; // x is the object_name
// initialize the data members of x;
x.realPart = 3.0;
x.imagPart = - 2.2;

example 2

struct ComplexNumber
{
    double realPart;
    double imagPart;
};

// declare a variable of type ComplexNumber
// and initialize using an initializer list
ComplexNumber x = {1.0, 2.3}

example 3

//define the new type ComplexNumber and declare two variables
// x and y of type ComplexNumber
struct ComplexNumber
{
    double realPart;
    double imagPart;
} x, y; 

//initialize x and y
x.realPart = 3.0;
x.imagPart = - 2.2;
y = x; // copy the entire structure y into x

example 4

//define a new anonymous type and declare a variable
// x with this type
struct 
{
    double realPart;
    double imagPart;
} x; 

//initialize x and y
x.realPart = 3.0;
x.imagPart = - 2.2;

3. Pointers to struct

• Like any other type, structures can be pointed to by its own type of pointers

• To access a member of a pointer to struct we use the -> opterator
  object_pointer_name -> member_name;

• Examples

example 1

//define the new type ComplexNumber
struct ComplexNumber
{
    double realPart;
    double imagPart;
};

// declare a variable of type complexNumber
complexNumber x = {1.0, 1.0};
complexNumber *ptr = &x; // a pointer to x

// print the data members of y
cout << ptr->realPart << "," << ptr->imagPart << endl;

example 2

struct TreeNode
{
    int val;
    TreeNode *left; //member_type：TreeNode*, member_name left;
    TreeNode *right;
    TreeNode(int x): val(x), left(NULL), right(NULL) {} //constructor
};

// initialized by constructor
// val = x, left -> NULL, right -> NULL
// there is no object_name

TreeNode *root; // root is object_pointer_name
auto p = root; 
while (p) p = p -> left;

example 3

class Trie {
public:
    struct Node
    {
        bool is_end; //member_type：bool, member_name is_end;
        Node *son[26]; // member_type：Node*, member_name son;
        // default constructor
        Node()
        {
            is_end = false;
            for (int i = 0; i < 26; i ++ ) son[i] = NULL;
        }
    } *root; //object_name or object_pointer_name?

    /** Initialize your data structure here. */
    Trie() {
        root = new Node();
    }

    void insert(string word) 
    {
        auto *p = root;
        for (auto c : word)
        {
        int u = c - 'a';
        if (p->son[u] == NULL) p->son[u] = new Node();
        p = p->son[u];
        }
        p->is_end = true;
    }
};

4. struct dynamic allocation

• struct variables can be allocated dynamically with new and delete
• we can also create arrays of stuct
• Examples

example 1

//define the new type ComplexNumber
struct ComplexNumber
{
    double realPart;
    double imagPart;
};

// declare a pointer variable of type ComplexNumber
complexNumber *ptr = NULL;
ptr = new ComplexNumber; // allocate memory

//initialize x and y
ptr -> realPart = 3.0;
ptr -> imagPart = - 2.2;

// print the data members of y
cout << ptr->realPart << "," << ptr->imagPart << endl;

delete ptr; // de-allocate memory

example 2

//define the new type ComplexNumber
struct ComplexNumber
{
    double realPart;
    double imagPart;
};

// declare a pointer variable of type ComplexNumber
complexNumber *ptr = NULL;
ptr = new ComplexNumber[2]; // allocate memory for an array of size 2

//initialize x and y
ptr[0].realPart = 3.0; // note we are using '.' not '->'
ptr[0].imagPart = - 2.2;
ptr[1] = ptr[0]; 

// print the data members of y
cout << ptr->realPart << "," << ptr->imagPart << endl;

delete[] ptr; // de-allocate memory