c - 分配与初始化 : Initializing structs inside another struct in C

Question

我有一个包含两个字段的结构，它们本身就是结构。我想使用初始化列表来分配内部结构的字段，而不必手动分配每个字段。

struct point
{
    int x;
    int y;
};

struct rectangle
{
    struct point p1;
    struct point p2;
};

struct rectangle r2;
r2.p1 = {5, 6};
r2.p2 = {7, 20};

但是这段代码无法编译:

structs3.c:105:11: error: expected expression before ‘{’ token
   r2.p1 = {5, 6};
           ^
structs3.c:106:11: error: expected expression before ‘{’ token
   r2.p2 = {7, 20};
           ^

为什么这行不通？这是什么原因？

Answer 1

你可以在定义 r2 时这样做，比如

struct rectangle r2 = {
    {5, 6},
    {7, 20}
};

或使用 compound literals如

r2.p1 = (struct point){5, 6};
r2.p2 = (struct point){7, 20};