哪个大哥能给我解释解释这么写什么来头~？

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

struct TEST {
    int aa;
    int bb;
};

int main()
{
    struct TEST *test = malloc(sizeof(test));
    *test = (struct TEST) {　　　　//此处不加前边那个 (struct TEST) 会报错！
        .aa = 10,
        .bb = 20,
    };

    printf("%d %d\n", tset->aa, test->bb);

    return 0;
}

struct TEST {
    int aa;
    int bb;
} test = {10, 20};

struct TEST {
    int aa;
    int bb;
} test = {
    .aa = 10,
    .bb = 20,
};