C Primer Plus Chapter 14 (structure and other data forms)

1. Create a structure statement

• Structure statement （structure declaration） Describes the organizational layout of a structure
  • Each part of the structure is called member （member） or Field （field）

struct animal {
    
    char name[50];
    int age;
    char sex;
};

struct animal dog;
struct animal cat;

• Structure declarations are sometimes called templates , Because it outlines how the structure stores data

• If you put a structure declaration inside a function , Its tag is limited to the internal use of the function

• If you put the structure declaration outside a function , All functions after this declaration can use its tag

2. Define structural variables

• structure There are two meanings

  • Structural layout ： Tell the compiler how to represent data , But it doesn't make the compiler for data Distribute Space

  • Create a Structural variables

    struct animal {
            
        char name[50];
        int age;
        char sex;
    };
    
    struct animal dog;
    

    • The compiler creates a structure variable dog

    • The compiler uses animal The template allocates space for this variable

      • One contains 50 An element of char Array
      • One int Variable of type
      • One char Variable of type

    • These storage spaces are associated with a name dog Bind together

    • You can define two struct animal Variable of type , Or point to struct animal Pointer to type structure

      struct animal dog;
      struct animal cat;
      struct animal *a;
      

      • The pointer a Can point to dog 、cat Or any other animal Structural variables of type

    • From the nature ,animal The structure declaration creates a structure called struct animal New type of

struct animal dog;

• Is a simplification of the following statement

struct animal {
    
    char name[50];
    int age;
    char sex;
} dog;

struct {
     //  No structural markers 
    char name[50];
    int age;
    char sex;
} dog;

3.1 Initialization structure

struct animal {
    
    char name[50];
    int age;
    char sex;
};

struct animal dog = {
    
    "abc",
    1,
    'M'
};

• If you initialize the structure of a static storage period , The value in the initialization list must be a constant expression

3.2 Access structure members

#include <stdio.h>

struct animal {
    
    char name[50];
    int age;
    char sex;
};

int main() {
    
    struct animal dog = {
    
        "abc",
        1,
        'M'
    };

    printf("name = %s, age = %d, sex = %c\n", dog.name, dog.age, dog.sex);
}

3.3 Structure initializer

• C90 and C11 It provides Specify initializer （designated initializer）

struct animal dog = {
    
    .age = 1,
    .name = "abc",
    2,
    .sex = 'M'
};

• Dot operator + The member name method does not need to consider the order of members in the structure
• name The next one is age, therefore age From the original 1 Modified into 2

4. Structure array

4.1 Declare structure array

struct animal zoo[10];

• Every element in an array is a animal The structure of the type

4.2 Identify the members of the structure array

zoo;					// animal  Array of structures 
zoo[0]					// animal  Elements of the structure 
zoo[0].name = "abc";	// char  Array 
zoo[0].name[1] = 'b';	// char

5. Nested structure

struct name {
    
    char first[10];
    char last[10];
};

struct animal {
    
    struct name dog;
    int age;
    char sex;
};

6. Pointer to structure

• Pointers to structures are usually easier to manipulate than the structure itself
• You can pass a pointer to a structure to a function
• Passing pointers is more efficient
• The structure representing data contains pointers to other structures

6.1 Declare and initialize structure pointers

struct animal* p;

p = &dog;

printf("%#x\n", p);

• The structure variable name is not the address of the structure variable

6.2 Use pointers to access members

• Access member's 2 Methods

  • The first 1 Methods ： Use -> Operator

    printf("%s\n", p->name);
    

  • The first 2 Methods ： Quoting

    printf("%s\n", (*p).name);
    

7. Passing information about structures to functions

7.1 Pass structure members

#include <stdio.h>

struct animal {
    
    char name[50];
    int age;
    char sex;
};

void sout(char);

int main() {
    
    struct animal dog = {
    
        .name = "abc",
        .age = 1,
        .sex = 'M'
    };

    sout(dog.name);
}

void sout(char str[50]) {
    
    printf("%s\n", str);
}

7.2 The address of the delivery structure

#include <stdio.h>

void sout(struct animal *);

struct animal {
    
    char name[50];
    int age;
    char sex;
};

int main() {
    
    struct animal dog = {
    
        .name = "abc",
        .age = 1,
        .sex = 'M'
    };

    sout(&dog);
}

void sout(struct animal *p) {
    
    printf("%s\n", p->name);
}

7.3 Transmission structure

#include <stdio.h>

void sout(struct animal);

struct animal {
    
    char name[50];
    int age;
    char sex;
};

int main() {
    
    struct animal dog = {
    
        .name = "abc",
        .age = 1,
        .sex = 'M'
    };

    sout(dog);
}

void sout(struct animal a) {
    
    printf("%s\n", a.name);
}

7.4 Other structural features

• Assign one structure to another

  dog = cat;
  

7.5 Structure and structure pointer selection

• The pointer ：

  • advantage ：

    • C A method that language can always use

    • Faster execution , Just pass an address

  • shortcoming ：

    • Unable to protect data

• structure ：

  • advantage ：
    • The function deals with a copy of the original data , Protecting raw data
    • The code style is clear
  • shortcoming
    • Older versions cannot be used
    • Transfer structure wastes time and storage space

• In pursuit of efficiency, structural pointers are used as function parameters , Use const Prevent accidental modification

• Passing structures by value is the most common way to deal with small structures

7.6 The character array and character pointer in the structure

struct name {
    
    char *first;
    char *last;
};

struct name n = {
    
    "abc",
    "ABC"
};

printf("%s, %s\n", n.first, n.last);

7.7 structure 、 Pointers and malloc()

• Use malloc() Allocate memory and use a pointer to store the address , Allocate appropriate space for the string

struct name {
    
    char* first;
    char* last;
};

char first[5];
char last[5];

fgets(first, 5, stdin);
fgets(last, 5, stdin);

struct name n;

n.first = (char*)malloc(strlen(first) + 1);
n.last = (char*)malloc(strlen(last) + 1);

strcpy(n.first, first);
strcpy(n.last, last);

printf("%s%s\n", n.first, n.last);

7.8 Compound literals and structures （C99）

struct animal dog;
dog = (struct animal) {
    
    .name = "abc",
    .age = 1,
    .sex = 'M'
};

7.9 Scalable array members （C99）

• utilize Scalable array members （flexible array member） Structure of declaration , Features of the last array member
  • The array will not exist immediately
  • Using this scalable array member, you can write appropriate code
• Rules for declaring scalable array members
  • Must be the last member of the structure
  • Structure must have at least one member
  • The declaration of a scalable array is similar to an ordinary array

struct animal {
    
    int age;
    char sex;
    char name[]; //  Scalable array members 
};

• You need to declare a struct animal Type of The pointer , And then use malloc() To allocate enough space , To store the struct animal The general contents of the type structure and the extra space required for the scalable array members

struct animal *p;
p = malloc(sizeof(struct animal) + 5 * sizeof(char));

7.10 Anonymous structure （C11）

struct animal {
    
    struct {
    
        char first[10];
    	char last[10];
    };
    int age;
    char sex;
};

8. The chain structure

• data structure ：
  • Binary tree
  • Pile up
  • Hashtable
  • Chart
• These data structures are composed of The chain structure （linked structure） form
• Each structure contains one or two data items and one or two pointers to other structures of the same type
• These pointers link one structure to another , And provide a path that can traverse the entire structure linked to each other

9. Joint profile

• union （union） It's a data type , It can store different data types in the same memory space （ Not stored at the same time ）

union animal {
    
    char name[10];
    int age;
    char sex;
}

• Declared unions can only store name, age, sex A value of
• The compiler allocates enough space to store the type that takes up the largest bytes in the joint declaration

9.1 Use Union

union animal dog;
dog.name = "abc";	//  take  "abc"  Storage 
dog.age = 1;		//  Delete  "abc" , take  1  Storage 
dog.sex = 'M';		//  Delete  1 , take  'M'  Storage 

9.2 Anonymous Union （C11）

union animal {
    
    union {
    
        char first[10];
    	char last[10];
    };
    int age;
    char sex;
};

10. Enumeration type

• Enumeration type （enumerated type） Used to represent integer constants
• Use to enum Statement （enum Constant is int type ）
• Improve code readability

enum letter {
    a, b, c};
enum letter abc;

• The first 1 A declaration creates letter As a tag name , Allow to put enum letter Use as type name
  • Enumerated in curly brackets letter Variables may have values
• The first 2 A statement makes abc As a variable of this type
  • abc Possible values make a、b、c
  • These symbolic constants are called enumerator （enumerator）

10.1 enum Constant

printf("a = %d,b = %d\n", a, b);
// a = 0,b = 1

10.2 The default value is

• By default , The constants in the enumeration list are given 0、1、2 etc.

10.3 assignment

enum number {
     a, b = 10, c = 100 };

printf("a = %d,b = %d, c = %d\n", a, b, c);
// a = 0,b = 10, c = 100

10.4 Shared name space

• The name space （namespace） Used to identify various parts of the program , That is, identify by name
• Scope is part of the namespace
  • Variables with the same name in two different scopes do not conflict
  • Two variables of the same scope with the same name conflict
• Structure tags in a specific scope 、 Both union and enumeration tags share the same namespace , This namespace is different from the space used by ordinary variables
• In the same scope, the names of variables and tags can be the same , There will be no conflict , However, you cannot declare two tags or variables with the same name in the same scope

11. typedef brief introduction

• Use typedef You can customize the name for a type
• And #define similar , But there are two 3 Different
  • typedef The symbolic name created is limited to the type , Cannot be used for values
  • typedef Interpreted by the compiler , It's not a preprocessor
  • Within the limits ,typedef Than #define More flexible

typedef unsigned char BYTE;
//  use  BYTE  Express  1  Byte data type 

• Improve program portability

12. Other complex statements

• Symbols that can be used when declaring

Symbol	meaning
*	It means a pointer
()	Represents a function
[]	Represents an array

• *、()、[] Rules of priority

  • The first 1 strip

    • After the array name [] And after the function name () With the same priority
    • Their ratio * （ Quoting ） High priority

    int * i[10];
    //  An array containing pointers 
    

  • The first 2 strip

    • [] and () Same priority for , From left to right

    int (* i)[10];
    //  Pointer to array 
    

  • The first 3 strip

    • [] and () From left to right

    int i[10][20];
    // i  By  10  Contents  20  individual  int  A two-dimensional array consisting of an array of type values 
    
    int * i[10][20];
    // i  By  10  Contents  20  individual  int  A two-dimensional array consisting of an array of pointer type values , reserve  200  Memory space for two pointers 
    
    int (* i)[10][20];
    // i  By  10  Contents  20  individual  int  Pointer to a two-dimensional array consisting of an array of type values , reserve  200  individual  int l Storage space