是否返回语句复制值

I am wondering about this because of scope issues. For example, consider the code

typedef struct {
    int x1;/*top*/
    int x2;/*bottom*/
    int id;
} subline_t;



subline_t subline(int x1, int x2, int id) {
    subline_t t = { x1, x2, id };
    return t;
}

int main(){
    subline_t line = subline(0,0,0); //is line garbage or isn't it? the reference
    //to subline_t t goes out of scope, so the only way this wouldn't be garbage
    //is if return copies
}

所以我的问题是，return 语句会一直复制吗?在这种情况下，它似乎有效，所以我被引导相信 return 确实复制了.如果它确实复制，它会在每种情况下都复制吗?

subline_t &subline(int x1, int x2, int id) {