CODEWITHSUNDEEP
c++class
goldenmean
goldenmean

Reputation: 19026

Accessing a variable in a union which is inside a class

Sorry for naive question in C++. For below code, there is a class, inside which there is a union declaration having two variables. How to access the variables in the union using the class object in code below:

class my
{

public:
//class member functions, and oeprator overloaded functions

 public:

    union uif
    {
    unsigned int    i;
    float       f;
    };

private:
//some class specific variables.

};

if there is an object of type my defined like 

my v1;

in a function later

Using v1 how do i access float f; inside union above in code?

also I want to watch the value of this float f in the watch window of a debugger(VS-2010), how to do that?

I tried v1.uif.f , this gave error in the watch window as : Error oeprator needs class struct or union.

v1.

Upvotes: 4

Views: 4557

Answers (6)

PZX_XY
PZX_XY

Reputation: 25

Although the union declaration is added to the class, no object is created. For example, you want to build a robot from a puzzle, and now you have designed the puzzle, but you haven't finished it yet.

Upvotes: 0

Mooing Duck
Mooing Duck

Reputation: 66971

One option I don't see already here is that of an Anonymous Union, which is where you have no type or instantiation. Like so:

class my 
{ 
public: 
//class member functions, and oeprator (sic) overloaded functions 

    function(int new_i) { i = new_i;}
    function(float new_f) { f = new_f;}
 public: 

    union /* uif */
    { 
    unsigned int    i; 
    float       f; 
    }; 

private: 
//some class specific variables. 

}; 

my m;
m.i=57;
m.f=123.45f;

Remember that with unions, it is only defined to read from the last member variable written to.

Upvotes: 1

Michael Goldshteyn
Michael Goldshteyn

Reputation: 74430

You are only defining the union within the scope of the class, not actually creating a member variable of its type. So, change your code to:

class my 
{ 

public: 
//class member functions, and oeprator (sic) overloaded functions 

 public: 

    union uif 
    { 
    unsigned int    i; 
    float       f; 
    } value; 

private: 
//some class specific variables. 

};

Now you can set the member variables in your union member, as follows:

my m;

m.value.i=57;
// ...
m.value.f=123.45f;

Upvotes: 5

Sarfaraz Nawaz
Sarfaraz Nawaz

Reputation: 361682

You've only defined the type of the uniion, you've not yet declared an object of this union type.

Try this:

class my
{
public:
    union uif
    {
      unsigned int    i;
      float       f;
    };

    uif obj;  //declare an object of type uif
};

my v;
v.obj.f = 10.0; //access the union member

Upvotes: 2

Codie CodeMonkey
Codie CodeMonkey

Reputation: 7946

You have defined your union in your class, but you haven't created an instance of it! Try:

union uif
{
unsigned int    i;
float       f;
} myUif;

And then use v1.myUif.f (or i).

Upvotes: 0

Puppy
Puppy

Reputation: 146998

You never actually defined any member of that union. You only ever defined the union itself. There is no spoon float.

Upvotes: 4

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