4.2 结构类型——结构

1. 结构

#include<stdio.h>int main(int argc, const char *argv){    struct date{        int month;        int day;        int year;    };    struct date today;    today.month = 02;    today.day = 16;    today.year = 2017;    // Today is 2017-2-16    printf("Today is %i-%i-%i\n", today.year, today.month, today.day);    return 0;}

2.声明在函数内外

和本地变量一样：

• 在函数内部声明的结构类型，只能在函数内部使用
• 在函数外部声明的结构类型，可以被多个函数使用，通常在函数外部

3.声明结构的形式

    // 方式一     struct point {        int x;        int y;    };    struct point p1, p2;// p1 和 p2 都是point，都有x y    // 方式二    struct {        int x;        int y;    } p1, p2; //没有声明 point, p1, p2 是一种无名结构，有 x y    // 方式三    struct point{        int x;        int y;    } p1, p2; // p1 p2 都是point，里边有 x y 

4.结构的初始化

#include<stdio.h>struct date {    int month;    int day;    int year;};int main(int argc, const char *argv){    struct date today = { 02, 16, 2017 };    printf("Today is %i-%i-%i\n", today.year, today.month, today.day); // Today is 2017-2-16    // .c 文件支持，.cpp 不支持会报错：sorry, unimplemented: non-trivial designated initializers not supported     struct date Month = {.year = 2017, .month = 02};     printf("this month is %i-%i-%i\n", Month.year, Month.month, Month.day); // this month is 2017-2-0    return 0;}

5. 结构成员

变量名.成员名

#include<stdio.h>struct date {    int month;    int day;    int year;};int main(int argc, const char *argv){    struct date today = { 02, 16, 2017 };    printf("Today is %i-%i-%i\n", today.year, today.month, today.day); // Today is 2017-2-16    return 0;}

6.结构运算

• 用结构变量的名字 访问整个结构
• 对于整个结构，可以做 赋值、取地址、函数参数
  
  • p1 = (struct point){5, 10}; // 相当于 p1.x = 5; p1.y = 10;
  • p1 = p2; // 相当于 p1.x = p2.x; p1.y = p2.y;

#include<stdio.h>struct date {    int month;    int day;    int year;};int main(int argc, const char *argv){    struct date today;    today = (struct date){ 02, 16, 2017 };    struct date day;    day = today;    day.year = 2015;    printf("day is %i-%i-%i\n", day.year, day.month, day.day); // day is 2015-2-16    return 0;}

7. 结构指针

用 & 取结构体的地址

#include<stdio.h>struct date{    int month;    int day;    int year;};int main(int argc, const char *argv){    struct date today;    today = (struct date){ 02, 16, 2017};    struct date *pDate = &today;    printf("address of today is %p\n", today); // address of today is 000000000022FE20    printf("address of pDate is %p\n", pDate); // address of pDate is 000000000022FE30    printf("pDate=%X\n", *pDate); // pDate=22FE20    return 0;}

8. 结构作为函数参数

int numberOfDay(struct date d)

• 整个结构可以作为函数参数，在函数内新建一个结构变量，并复制调用者的结构的值
• 函数可以返回一个结构

输入今天的日期，打印明天的日期

#include<stdio.h>#include<stdbool.h>struct date{    int month;    int day;    int year;};bool isLeap(struct date d);int numberOfDays(struct date d);int main(int argc, const char *argv){    struct date today, tomorrow;    printf("输入今天的日期(mm dd yyyy)："); // 输入今天的日期(mm dd yyyy)：02 16 2017    scanf("%i %i %i", &today.month, &today.day, &today.year);    if(today.day != numberOfDays(today)){        tomorrow.day = today.day + 1;        tomorrow.month = today.month;        tomorrow.year = today.year;    } else if(today.month == 12) {        tomorrow.day = 1;        tomorrow.month = 1;        tomorrow.year = today.year + 1;    } else {        tomorrow.day = 1;        tomorrow.month = today.month + 1;        tomorrow.year = today.year;    }    // Tomorrow's date is 2017-2-17    printf("Tomorrow's date is %i-%i-%i\n", tomorrow.year, tomorrow.month, tomorrow.day);    return 0;}int numberOfDays(struct date d){    int days;    const int daysPerMonth[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};    if(d.month == 2 && isLeap(d)){        days = 29;    } else {        days = daysPerMonth[d.month - 1];    }    return days;}bool isLeap(struct date d){    bool leap = false;    if((d.year % 4 == 0 && d.year % 100 != 0) || d.year % 400 == 0){        leap = true;    }    return leap;}

9.输入结构

没有直接的方式可以一次 scanf 一个结构，比如我们有一个函数 用于读入一个坐标的x y值，该函数中可以操作这个结果，但是怎么传出去呢？
可以在函数中，创建一个临时的结构变量，然后 返回这个结构变量

#include<stdio.h>struct point {    int x;    int y;};struct point getPoint(void);void printPoint(struct point);int main(int argc, const char *argv){    struct point y = {0,0};    y = getPoint();    printPoint(y);    return 0;}struct point getPoint(){    struct point p;    scanf("%d", &p.x);// 输入 2 回车 3 回车    scanf("%d", &p.y);    printf("getPoint x=%d, y=%d\n", p.x, p.y); // getPoint x=2, y=3     return p;}void printPoint(struct point p){    printf("printfPoint x=%d, y=%d\n", p.x, p.y); // printfPoint x=2, y=3}

10.指向结构的指针 作为参数

当传递给函数 一个很大的结构，传指针 比 结构 更高效

用 -> 表示指针所指的结构变量中的成员

#include<stdio.h>struct point {    int x;    int y;};struct point* getPoint(struct point*);void printPoint(const struct point*);int main(int argc, const char *argv){    struct point y = {0,0};    getPoint(&y);    printPoint(&y);//  printPoint(getPoint(&y));    return 0;}struct point* getPoint(struct point* p){    scanf("%d", &p->x);// 输入 2 回车 3 回车    scanf("%d", &p->y);    printf("getPoint x=%d, y=%d\n", p->x, p->y); // getPoint x=2, y=3    return p;}void printPoint(const struct point *p){    printf("printfPoint p->x=%d, p->y=%d\n", p->x, p->y); // printfPoint p->x=2, p->y=3}

11.结构数组

#include<stdio.h>struct time{    int hour;    int minute;    int second;};struct time timeUpdate(struct time now);int main(int argc, const char *argv){    struct time times[] = {        {11, 59, 59},        {12, 1, 0},        {1, 29, 59},        {23, 59, 59},        {19, 12, 27}    };    int i;    for(i = 0; i < 5; i++){        printf("Time is %.2i:%.2i:%.2i\n", times[i].hour, times[i].minute, times[i].second);        times[i] = timeUpdate(times[i]);            printf("1s laster, Time is %.2i:%.2i:%.2i\n", times[i].hour, times[i].minute, times[i].second);    }    return 0;}// 计算1s之后的时间并返回 struct time timeUpdate(struct time now){    ++now.second;    if(now.second == 60){        now.second = 0;        ++now.minute;        if(now.minute == 60){            now.minute = 0;            ++now.hour;            if(now.hour == 24) {                now.hour = 0;            }        }    }    return now;}

12.嵌套的结构

struct point{    int x;    int y;};struct rectangle{    struct point p1;    struct point p2;};// 如果有  struct rectangle r; 就可以有 r.p1.x  r.p2.y// 如果有： struct rectangle r, *rp;rp = &r;// 下边四种形式是等价的 r.p1.x;rp->p1.x;(r.p1).x;(rp->p1).x; 

13.结构中的结构数组

#include<stdio.h>struct point{    int x;    int y;};struct rectangle{    struct point p1;    struct point p2;};void printRec(struct rectangle r){    printf("<%d,%d> to <%d,%d>\n", r.p1.x, r.p1.y, r.p2.x, r.p2.y);}int main(int argc, const char *argv){    struct rectangle rects[] = {        {{1, 2}, {3, 4}},        {{5, 6}, {7, 8}}    };    int i;    for(i = 0; i < 2; i++){        printRec(rects[i]);    }    return 0;   }