C Language -- struct, C language --

C Language -- struct, C language --
I. struct 1. Definition of struct Variables

* Struct can be composed of multiple different types of data.

* Struct Person {int age; double height; char * name}; // first defines the struct type, which has three members or attributes.

* Struct Person p = {18, 1.80, "jack"}; // define the variable based on the struct type and initialize it.

2. assign values to struct variable attributes

1> variable attribute Assignment 1

Struct Person p = {18, 1.80, "jack "};

// Modify attributes

P. age = 20;

P. height = 1.78;

P. name = "rose ";

P = {19, 1.77, "jame"}; // incorrect value assignment method. The variable can only be initialized when it is defined.

2> struct variable value assignment 2

Struct Person p2 = {. age = 19;. height = 176;. name = "tom "};

3. Structure memory Analysis

1> struct Date {int year; int month; int day}; // the code in this row only defines a struct type and no storage space is allocated.

2> struct Date d1 = {2011,4, 10}; // defines the struct variable (actually allocating storage space ), the storage space of struct variables is the sum of all its variables-12 bytes, which can be detected by sizeof (d ).

3> struct Student {int age; char * name };

Struct Student stu = {18, "jary"}; // The struct variable occupies 16 bytes. Because when the struct volume changes to different types of data, the storage space is a multiple of the maximum types of data bytes.

4. Multiple definitions of struct Variables

1> struct Person {int age; double height; char * name };

Struct Person p = {18, 1.80, "jack "};

2> struct Person {int age; double height; char * name} p1; // defines the variable while defining the struct

Struct Person {int age; double height; char * name} p2; // incorrect syntax, repeated definition of struct type

3> struct {int age; double height; char * name} p3; // disadvantage: Repeated variables cannot be defined.

5. struct Scope

* The struct type also has a scope, starting from the row that defines the type until the end of the code block.

* Global variables and local variables can be compared for definition and use.

6. struct Array

1> struct array Definition

Struct Person {int age; double height; char * name };

Struct Person names [3] = {18, 1.80, "jack" },{ 18, 1.80, "jame" },{ 18, 1.80, "tom "}};

7. pointer to struct

1> pointer Definition

Struct Person {int age; double height; char * name}; // defines the type.

Struct Person p1 = {18, 1.80, "jack"}; // defines the struct variable

Struct Person * p; // defines the pointer of the struct Person type.

P = & p1; // pointer Variable p points to the p1 variable

2> how to access struct variable attributes

① P1.age; p1.height; p1.name; // use the variable name for direct access

② (* P). age; (* p). height; (* p). name; // access by pointer

③ P-> age; p-> height; p-> name; // use the pointer arrow

8. nested struct

1> struct Date {int year; int month; int day };

Struct Student {int age; double height; struct Date birthday}; // nested struct Definition

Struct Student stu = {18,188, {, 9 }};

Ii. Summary of data types 1. Basic Data Types

1> int

① Long int, long: 8 bytes % ld

② Short int and short: 2 bytes % d and % I

③ Unsigned int and unsigned: 4 bytes % d and % I

④ Signed int and signed: 4 bytes % d and % I

2> float/double

① Float: 4 bytes % f

② Double: 8 bytes % f

3> char

① 1 byte % c, % d

② The ASCII value of the char type stored in the memory; 'A' --> 65

2. Construction type

1> array: Only data of the same type can be stored.

Definition: data type array name [number of elements]

2> struct: It can be composed of multiple different types of data.

Definition: Define type reuse type definition variable first

3. pointer type

1> variable definition: int * p;

2> indirect operation variable value, int a = 10; int * p; p = & a; * p = 20;

4. Enumeration type

1> usage: When a variable has only a few fixed values