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Using struct and Union

hipooja

Hi,

I have used class to model different parts of VE ranging from the data structure to drivers ,generator , monitor ...Class is a collection

of different data types so is a struct and a union.The difference i know is that union occupies memory equal to its largest data element unlike a struct or a class and secondly a struct can contain a union ,even a class can have a nested class object.

 My questions is ,where do we use struct and union.Have you used them in modelling data or any other element of the VE and why?

How do i differentiate as to where should i be using a class/struct/union.

 

Regards,

Pooja Vaishnav 

 

  • A struct is an array of data objects. it can be packed or unpacked but only packed structs can be used in synthesizable code. The following is a packed struct because it consists of only literals.

    struct packed {

      logic [15:0] addr;

      logic [31:0] data;

      bit          parity;

    } frame;

    A union allows the specification of multiple representations for the same data element.

    union {

      int        i;

      reg [31:0] r;

    } data;

    The data object holds a single 32-bit value but can have it represented as a 2-state integer or a 32-bit 4-state reg depending on whether you access it use the “I” or “r” type.

    Now you can put these two constructs together as so:

    struct {

      logic [15:0] addr;

      union {

        int        i;

        reg [31:0] r;

      } data;

      bit          parity;

    } frame;


    Tim

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