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How/Where/when to use unions

hipooja

I understand union to be a user defined data type that can store variables of different data types,however unlike class they do not contain methods to operate on the properties and they occupy the same memory as the largest data in them.

I however do not know How ,when ,where and why to use unions as i have used classes extensively but not tried my hand at unions

I wrote a simple code ,my idea was to display the properties of the union num ,defined below.i also want to know if unions and structs have a constructor like classes?

program p1;
typedef union packed {

int i;
real f;
} num ;

num n1 , n2;
n1.f = 0.5;
n2.i = -44;
$display("f = %h\n",n1.f);
endprogram

 

I declareed the union to be packed as it otherwise issued an error that unpacked unions are unsupported,Secondly cant we define unions independently ,the way we define classes? I get a syntacx error at n1.f = 0.5 ,can you help me understand and use unions better?

 

Regards,

Pooja

Parents

  • Hi Pooja,

    Basically you use unions to have different interpretations of a single daya type.

     

    Please check the following code, i have not used packed here and unpacked will work here. You missed the initial begin-end block. Other than that your code is flawless.

     program p1;
    typedef union packed {
    int i;
    real f;
    } num ;

    num n1 , n2;
    initial begin
    n1.f = 0.5;
    n2.i = -44;
    $display("f = %f\n",n1.f);
    end
    endprogram

Reply

  • Hi Pooja,

    Basically you use unions to have different interpretations of a single daya type.

     

    Please check the following code, i have not used packed here and unpacked will work here. You missed the initial begin-end block. Other than that your code is flawless.

     program p1;
    typedef union packed {
    int i;
    real f;
    } num ;

    num n1 , n2;
    initial begin
    n1.f = 0.5;
    n2.i = -44;
    $display("f = %f\n",n1.f);
    end
    endprogram

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