error trying to get data member field

[adam2016]

Hi guys this question is asked after I did some research on Unions I followed tutorials but for some reason I am getting a compilation error,I have a union but it contains three different structs I want to be able to call the structs data types or even change them

the error is as follows

Description Resource Path Location Type
Field 'a' could not be resolved Main.cpp /nameSpaces line 38 Semantic Error

how do I solve this problem?

  union numbers{

	struct one{

		int type = 1;
		int a = 6;
	};OPTION_INT;

	struct two{

			int type = 2;
			char b = 'a';

		};OPTION_CHAR;

	struct three{

			int type = 3;
			double c = 7.2;

		};OPTION_DOUBLE;
};

int main()
{

    numbers t; // this is fine
    int n = t.a; // this is where I get the error

}
    

*edit

I also tried this

int n = t.one.type;

but still got an error

[coder777]

Well, OPTION_INT is not related to one because of the ; in front of it. The same applies to the other OPTION_.... So remove the ;.

The second problem is that you cannot initialize members of a union. Everything within the union will be stored in one place. Which of the values are supposed to be used there?

[adam2016]

I'm still getting an error,I tried searching for the error online but got no results

union numbers{



struct one{

	int type = 1;
	int a = 6;
	}OPTION_INT;

struct two{

	int type = 2;
        char b = 'a';

	}OPTION_CHAR;

struct three{

	int type = 3;
	double c = 7.2;

	}OPTION_DOUBLE;
};

int main()
{



    numbers number;
    number.OPTION_CHAR.type = 5;
}

the error is Description Resource Path Location Type
union member 'numbers::OPTION_CHAR' with non-trivial 'constexpr numbers::two::two()' Main.cpp /nameSpaces line 25 C/C++ Problem

and it's the same for OPTION_INT and OPTION_DOUBLE

Description Resource Path Location Type
use of deleted function 'numbers::numbers()' Main.cpp /nameSpaces line 40 C/C++ Problem

Also this one that does not make sense since sense since I don't have a function named numbers()

[lastchance]

@adam2016 - you haven't noted what @coder777 wrote:

you cannot initialize members of a union

#include <iostream>

union numbers{


struct one{

        int type;
        int a;
        }OPTION_INT;

struct two{

        int type;
        char b;

        }OPTION_CHAR;

struct three{

        int type;
        double c;

        }OPTION_DOUBLE;
};

int main()
{
    numbers number;
    number.OPTION_CHAR.type = 5;

    std::cout << number.OPTION_INT.type << '\n';
    std::cout << number.OPTION_CHAR.type << '\n';
    std::cout << number.OPTION_DOUBLE.type << '\n';
}

[JLBorges]

> you cannot initialize members of a union

The first non-static data member of the union can be initialised with a brace enclosed initialiser
The braces may be omitted if the union is a data member of an aggregate.
A union which does not have a deleted copy/move constructor can be copy/move initialised.

int main()
{
    union U { int i ; char cstr[23] ; };
    U u1 {23} ;
    U u2 = u1 ;
    u1 = {999} ;

    struct S { U u ; double d ; } ;
    S s1 { {456}, 78.9 } ;
    S s2 { 4567, 89.0123 } ;
    s1 = { 11, 22.33 } ;
}

Needless to say, a union may also be initialised via a user-defined constructor:

#include <string>

int main()
{
    union U
    {
        U() = default ;
        U( int i ) : i(i) {}
        U( double d ) : d(d) {}
        U( const std::string& str ) : d( std::stod(str) ) {}
        U( const char* cstr ) : U( std::string(cstr) ) {}

        int i = 0 ;
        double d ;
    };

    U u1 = 45 ;
    U u2 = 67.84 ;
    U u3 = "23.456" ;
};