Why doesn't compound literals assignment work

问题:

I have a question about literals in C.

int a;
//a is an integer that is assigned an integer literal 414
a = 414;

float b;
//b is a float that is assigned a float literal of 3.14
b = 3.14;

struct point {
    int x,y;
};

struct point b;
//{5,6} is a compound literal that is assigned to a struture.
b = {5,6}; //doesn't work.

b = (struct point){5,6}; //works.

That doesn't seem to work without a typecast? What is the reason for this?

回答1:

(struct point){5,6} as a whole is a compound literal.

C11 §6.5.2.5 Compound literals

A postfix expression that consists of a parenthesized type name followed by a brace enclosed list of initializers is a compound literal.