如何在C中分配和声明结构数组的3D？

How do you allocate and declare a 3D array of structs in C? Do you first allocate the array or declare it? I feel like you have to allocate it first so you can declare it so it is on the heap, but then how do you allocate something that hasn't been made yet? Also, should you allocate it all at once or element by element? Also am i putting the structs into the array correctly? My guess on how to do it would be:How do you allocate and declare a 3D array of s