Accessing the variable within the union

Hi,

We are defining the union and structures mentioned below

typedef struct _var1_
{
int a;
int b;
}var1_t;

typedef struct _var2_
{
int c;
int d;
}var2_t;

typedef union _UVar
{
var1_t stVar1;
var2_t stVar2;
}UVar;

Created the instance like below.

UVar uVar;
UVar *puVar = &uVar;

Trying to access the element 'a ' as explained in below method

Method 1:

Accessing the  element  'a'  like below

puVar->stVar1.a 

was not working.

Method 2:

But typecasting the union pointer to the structure 

((var1_t*)puVar)->a ;

was working.

In most part of the code in our application, use method 1.

Why method 1 was not working? 

Is any configuration to be done to access the elements within the union?

Thanks & Regards,

K. lakshmanan