Purpose of Unions in C and C

I had previously used unions with ease, but when I read this post and learned that this code

union ARGB
{
    uint32_t colour;

    struct componentsTag
    {
        uint8_t b;
        uint8_t g;
        uint8_t r;
        uint8_t a;
    } components;

} pixel;

pixel.colour = 0xff040201;  // ARGB::colour is the active member from now on

// somewhere down the line, without any edit to pixel

if(pixel.components.a)      // accessing the non-active member ARGB::components

is in fact undefinable behaviour

For example, reading from a union member other than the one who has lately been written to results in undefinable behaviour.

What is the intended use of unions if not this?

Could someone kindly provide a detailed explanation?

Jul 13, 2022 in C++ by Nicholas
• 7,760 points • 322 views

No answer to this question. Be the first to respond.

Your answer

Your name to display (optional):

Email me at this address if my answer is selected or commented on:

Privacy: Your email address will only be used for sending these notifications.

Cases of static and dynamic binding in C++

When an object's static type is used to associate it with a member function, this is known as static binding (understand the type of its class). When a pointer or reference is associated with a member function based on the dynamic type of the object, this is known as dynamic binding (understand the instance of the variable at runtime). Before continuing, keep in mind that dynamic binding only works with pointers, references, and virtual functions for the base class. Because everything needed to call the function is known at compile time, the first call is a static binding (also known as early binding). Derived1 d1(1, 10); d1.display_data(); You already know that the d1 instance is a Derived1 automatic variable, and that it will call the Derived1::display data method (). The first condition is incorrect: d1 is neither a pointer nor a reference. The second condition isn't acceptable: There is no virtual Derived1::display data. The second call is for ...READ MORE

answered Jun 7, 2022 in C++ by Damon
• 4,960 points • 688 views

0 votes

0 answers

Use of min and max functions in C++

Are std::min and std::max better than fmin ...READ MORE

Jun 2, 2022 in C++ by Nicholas
• 7,760 points • 583 views

0 votes

1 answer

Use of min and max functions in C++

The functions fmin and fmax are designed ...READ MORE

answered Jun 21, 2022 in C++ by Damon
• 4,960 points • 11,229 views

0 votes

1 answer

functions in c++ call by value and call by reference

Calling a function by value copies the argument and stores it in a local variable for use by the function, so the argument is unaffected if the value of the local variable changes. The argument is passed to the function as a reference rather than a copy, so if the function changes the value of the argument, the argument is also changed. The void change(int); function prototype informs the compiler that there is a function named change that takes a single int argument and returns void (i.e. nothing). Because there is no & with the argument, it is called by value. You have the line change(orig); later in your code, which actually calls the function with. Take a look at the output of ...READ MORE

answered Jun 7, 2022 in C++ by Damon
• 4,960 points • 622 views

0 votes

0 answers

functions in c++ call by value and call by reference

The code below shows how to call a function in both methods. Please explain the major differences or meanings of call by value and call by reference to me. 1.Make a value-based call. 2.Call based on a reference. The call by value method is demonstrated in the following code. In a comment, I expressed my reservations. #include<iostream> int main(){ void change(int);//why function prototype is before ...READ MORE

Jun 6, 2022 in C++ by Nicholas
• 7,760 points • 497 views

0 votes

1 answer

Lower and Upper Bound in case of Decreasing/Non-ascending vector

Both std::lower bound and std::upper bound must have an increasing (non-decreasing) order as their objective. By giving a comparator as the 4th parameter of the functions, you may modify the meaning of "growing." To work with descending vectors, use std::greater. #include<iostream> #include<vector> #include<algorithm> #include<functional> using namespace std; int main() { ...READ MORE

answered Jun 14, 2022 in C++ by Damon
• 4,960 points • 1,213 views

0 votes

0 answers

Purpose of Unions in C and C++

I had previously utilised unions with ease; however, I was startled when I read this post and discovered that this code union ARGB { uint32_t colour; ...READ MORE