为什么初始化后可以使用结构初始化器而不是数组初始化器？

Question

Struct initializes can be used after initialization by casting it. Eg.

struct EST {
    int a;
    float b;
}est;

int main() {
    est = (struct EST){23, 45.4}; //This works nicely and est gets the values
    printf("a: %d\nb: %f\n", est.a, est.b);
}

But the same can't be done for arrays:

int arr[6];
arr = (int []){1, 2, 3, 4, 5};

This gives

error: assignment to expression with array type

What's more head breaking is that if there is an array in the struct, it still works.

struct Weird {
    int arr[6];
}w;

int main() {
    w = (struct Weird){{1, 2, 3, 4, 5}}; /* It works. The member arr gets all its elements
filled
*/
}

There seems to be something about the = operator not being valid with arrays after initializing. That is my theory.

Why is this and how can arrays be assigned after initializing?

Answer 1

initialization means initializing of a variable at declaration time. The following is correct and is supported by 'c':

int arr[6] = {1,2,3,4,5,6};

Assignment means assigning a value to a variable somwhere in the program after initialization. 'C' does not support assignment to a whole array. Arrays are very special members in 'c' and are treated in a special way which does not allow assignments.

However, you can always copy one array into another either by using a for loop or my using something like memcpy . Here is an example:

  int arr[6], brr[6] = {1,2,3,4,5,6};
  memcpy(arr,(int[6]){1,2,3,4,5},sizeof(int[6]));

BTW, the cast-like object from your example (int[]){1,2,3,4,5} is called 'compound literal' and is also allowed in c. Here it is used to initialize the parameter of the memcpy function.