C Language Learning 014: structured data types, language learning 014

C Language Learning 014: structured data types, language learning 014
Basic usage of struct

1 # include <stdio. h> 2 3 // define the data structure 4 struct fish {5 const char * name; 6 const char * species; 7 int teeth; 8 int age; 9 }; 10 11 void catalog (struct fish f) {12 printf ("% s is a % s with % I teeth. he is % I \ n ", f. name, f. species, f. teeth, f. age); // access structure field 13} 14 15 int main () {16 // declare the structure variable 17 struct fish snappy = {"Snappy", "Piranha ", 69,4}; 18 catalog (snappy); 19 return 0; 20}

When a structure variable is assigned to another structure variable, the computer creates a new structure copy and copies each field. If a pointer exists in the structure, only the pointer value is copied.

    struct fish snappy={"Snappy","Piranha",69,4};    struct fish gnasher=snappy;

The structure can also be nested

1 # include <stdio. h> 2 3 struct preferences {4 const char * food; 5 float exercise_hours; 6}; 7 8 struct fish {9 const char * name; 10 const char * species; 11 int teeth; 12 int age; 13 struct preferences care; // struct nested in fish preferences14}; 15 16 void catalog (struct fish f) {17 printf ("% s is a % s with % I teeth. he is % I \ n ", f. name, f. species, f. teeth, f. age); // access structure field 18 // structure 19 printf ("% s like to eat % s \ n", f. name, f. care. food); 20 printf ("% s like to exercise % f hours \ n", f.name,f.care.exe rcise_hours); 21} 22 23 int main () {24 struct fish snappy = {"Snappy", "Piranha", 69,4, {"Meat", 7.5 }}; 25 catalog (snappy); 26 return 0; 27}

Create more simple Structure Variables

By using typedef to name the structure, you can save the struct keyword when creating the structure variable.

# Include <stdio. h> typedef struct cell_phone {int cell_no; const char * wallpapaer;} phone; // phone is the type name (alias of cell_phone) int main () {phone p = {5555, "sinatra.png"}; printf ("number % I \ n", p. cell_no); return 0 ;}

We can also directly Save the name definition structure of the structure, which is called the anonymous structure.

1 typedef struct {2     int cell_no;3     const char *wallpapaer;4 } phone;

Transfer Structure pointer

When a structure is assigned to another structure, we know that a new copy is created. If we want to update the original structure through the structure to be assigned, we need to use the structure pointer.

1 # include <stdio. h> 2 3 typedef struct {4 int cell_no; 5 const char * wallpapaer; 6} phone; 7 8 int main () {9 phone p = {5555, "sinatra.png "}; 10 phone p2 = p; 11 p2.cell _ no = 4444; 12 printf ("p. cell_no: % I p2.cell _ no: % I \ n ", p. cell_no, p2.cell _ no); 13 phone * p3 = & p; // assign the address of structure p to * p314 (* p3 ). cell_no = 6666; 15 printf ("p. cell_no: % I p2.cell _ no: % I p3.cell _ no: % I \ n ", p. cell_no, p2.cell _ no, (* p3 ). cell_no); 16 return 0; 17}

Because we often write (* p2). wallpapaer errors as * p2.wallpapaer, they are not equivalent. Therefore, C language developers have designed a simpler method to Represent Structure pointers.

1 int main(){2      phone p={5555,"sinatra.png"};3      phone* p2=&p;4      printf("p2->wallpapaer:%s = (*p2).wallpapaer:%s\n",p2->wallpapaer,(*p2).wallpapaer);//5     return 0;6 }