学步园

typedef在编程中随处可见，大家都知道，它的作用无非有如下两种：

1、让代码更加简洁

2、让代码更加直观

3、其它更深层次的用途？？？？

如下面的例子：

#include <stdio.h>
#include <stdlib.h>

struct point
{
    int x;
    int y;
};

struct point* AddPoint(struct point *p1, struct point *p2)
{
    p1->x += p2->x;
    p1->y += p2->y;
    return p1;
}

int main()
{
    struct point p1 = {10, 20};
    struct point p2 = {30, 40};
    struct point TheAddPoint = *(AddPoint(&p1, &p2));
    printf("TheAddPoint x is %d y is %d", TheAddPoint.x, TheAddPoint.y);
    return 0;
}

那么用typedef，自定义两个别名(而非新建数据类型，注意是别名)：

typedef struct point Point;      

typedef struct point *PointPtr;

整个代码就可以改为：

#include <stdio.h>
#include <stdlib.h>

struct point
{
    int x;
    int y;
};

typedef struct point Point;
typedef struct point *PointPtr;

/*
struct point* AddPoint(struct point *p1, struct point *p2)
{
    p1->x += p2->x;
    p1->y += p2->y;
    return p1;
}
*/

PointPtr AddPoint(PointPtr p1, PointPtr p2)
{
    p1->x += p2->x;
    p1->y += p2->y;
    return p1;
}

int main()
{
    /*
    struct point p1 = {10, 20};
    struct point p2 = {30, 40};
    struct point TheAddPoint = *(AddPoint(&p1, &p2));
    */
    Point p1 = {10, 20};
    Point p2 = {30, 40};
    Point TheAddPoint = *(AddPoint(&p1, &p2));
    printf("TheAddPoint x is %d y is %d", TheAddPoint.x, TheAddPoint.y);
    return 0;
}

接下来，我们再来考虑其深层次的用途。