C language portal - type structure

First, the structure type declaration

#include <stdio.h>


int main(int argc, char const *argv[])
{
    // 声明结构类型
    struct date
    {
        int month;
        int day;
        int year;
    };
    
    // 使用自定义的类型
    struct date today;

    today.month = 9;
    today.day = 30;
    today.year = 2019;

    printf("Today is date is %i-%i-%i\n", today.year , today.month, today.day);


    return 0;
}

Second, in the function / outside?

1. And local variables, can only be used inside a function in the structure type declared inside a function
2. It is usually a function of the result type declared outside, so that a plurality of functions can be used

#include <stdio.h>

struct date
    {
        int month;
        int day;
        int year;
    };

int main(int argc, char const *argv[])
{
    
    struct date today;

    today.month = 9;
    today.day = 30;
    today.year = 2019;

    printf("Today is date is %i-%i-%i\n", today.year , today.month, today.day);

    return 0;
}

Third, the structure of the form of declaration

struct point{
    int x;
    int y;
}

struct point p1,p2;

// 其中p1和p2都是point
// 里面有x和y的值

There is another form:

struct{
    int x;
    int y
}p1 , p2 ;
// p1和p2都是一种无名结构，里面有x和y

Of course, there is a more common form

struct point {
    int x;
    int y;
}p1 , p2;

p1 and p2 are the point, which has values ​​of x and y

Fourth, the initialization structure

struct date{
    int month;
    int day;
    int year;
};

int main(int argc, char const *argv[])
{
    struct date taday = {9 , 30 , 2019};
    struct date thismonth = {.month=9 , .year=2019};

    printf("Today is date is %i-%i-%i\n", taday.year,taday.month,taday.day );
    printf("This month is %i-%i-%i\n", thismonth.year,thismonth.month,thismonth.day);

    return 0;
}
// Today is date is 2019-9-30
// This month is 2019-9-0

Structural member

1. A bit like structures and arrays
2. Array access its members a [10] = 10 with [] operator and subscripts;
3. Its members today.day access structure with "." Operator and name, student.firstName

Computing structure

1. To access the entire structure, the structure of the direct use of variable name
2. For the overall configuration, the assignment can be done, taking address, parameters may be passed to the function
3. p1 = (struct point) {5,10}; equal p1.x = 5, p1.y = 10;
4. p1 = p2; equal p1.x = p2.x; p1.y = p2.y;

Structure pointer

1. And an array of different, the name is not the address of the structure variable structure variable, you must use the & operator
2. struct date *pDate = &today;

V. Structure and Function

Structure as a function parameter

int numberOfDays(struct date d);

1. The entire structure can be passed as a function of the value of the parameter
2. Value at this time is to create a structure variable in the function and copy the caller's structure
3. It returns a structure may be
4. This is a completely different array

Input structure

1. There is no direct way a structure can be a scanf
2. If we are going to write a function that reads the results

#include <stdio.h>

struct point
{
    int x;
    int y;
};

void getStruct(struct point p);
void output(struct  point p);

int main()
{
    struct point y = {0,0};
    getStruct(y);
    output(y);
    
    return 0;
}


void getStruct(struct point p){
    scanf("%d" , &p.x);
    scanf("%d" , &p.y);
    printf("%d , %d\n", p.x , p.y);
}

void output(struct  point p)
{
    printf("%d , %d\n", p.x , p.y); 
}


// 2
// 3
// 2 , 3
// 0 , 0

1. But read the structure of how to send it back?
2. Remember when the c language function calls are passed by value, so the main function of p and y are in different

Solution to the problem

1. Previous embodiment, to a structure passed to the function and operation in a function, but does not return back
   • The problem is that the function is passed clone outside of that structure, rather than a pointer
   • Incoming structure and incoming arrays are different
2. In this input function, can create a temporary structure variable, then this structure is returned to the caller, but this is not common, you can understand

#include <stdio.h>

struct point
{
    int x;
    int y;
    
};

struct point getStruct(void);
void output(struct  point p);

int main()
{
    struct point y = {0,0};
    y = getStruct();
    output(y);
    
    return 0;
}


// 这里返回一个struct
struct point getStruct(void){

    struct point p; 
    scanf("%d" , &p.x);
    scanf("%d" , &p.y);
    printf("%d , %d\n", p.x , p.y);
    return p;
}

void output(struct  point p)
{
    printf("%d , %d\n", p.x , p.y); 
}

// 5 6
// 5 , 6
// 5 , 6

1. The most common is the structure pointer as a parameter

Sixth, the pointer to the structure

struct date
{
    int month;
    int day;
    int year;
}myday;

struct date *p = &myday;

(*p).month = 12;
p->month = 12;

By -> structure of a member in the pointer variable

Structure pointer parameter

struct point
{
    int x;
    int y;
    
};


struct point* getStruct(struct point *p);
void output(struct point p);
void print(const struct point *p);


int main(int argc, char const *argv[])
{
    struct point y = {0,0};
    getStruct(&y);
    output(y);
    output(*getStruct(&y));
    print(getStruct(&y));

    return 0;
}

struct point* getStruct(struct point *p)
{
    scanf("%d" , &p->x);
    scanf("%d" , &p->y);
    printf("%d , %d\n", p->x , p->y);
    return p;
}

void output(struct point p)
{
    printf("%d , %d\n", p.x , p.y);
}

void print(const struct point *p)
{
    printf("%d , %d\n", p->x , p->y);
}