Fix size buffer

Fixed size buffers are used to declare C style in-line arrays as members of structs. Fixed size buffers are primarily useful for interfacing with unmanaged APIs. Fixed size buffers are an unsafe feature, and fixed size buffers can only be declared in unsafe contexts.

A fixed size buffer is a member that represents storage for a fixed length buffer of variables of a given type. A fixed size buffer declaration introduces one or more fixed size buffers of a given element type. Fixed size buffers are only permitted in struct declarations and can only occur in unsafe contexts.

A fixed size buffer declaration that declares multiple fixed size buffers is equivalent to multiple declarations of a single fixed sized buffer declaration with the same attributes, and element types. 

unsafe struct A 
{ 
 public fixed int x[5], y[10], z[100];
}

unsafe struct A

{

   public fixed int x[5];

   public fixed int y[10];

   public fixed int z[100];

}

To declare fix size buffer, you need in C# Language Properties set Property Fixed value to true: