Unions

Unions are similar to structures but only one member within the union can be used at a time, due to it having a shared memory size for all members.

union identifier {
     char desc[50] ;
     float price ;
     int devs ;
     } ;

Unions are used when just one condition will be applied and only one variable is required.

#include <iostream>
using namespace std ;
 
union opSysName {
    char desc[50];
    float price;
    int devs;
} ;
 
int main() {
 
    union
    opSysName linux = {"fun, free and better!"} ;
    cout << "The best OS might just possibly be " << linux.desc ;
 
    /*set price - remembering that a union can only hold one variable at a time*/
  
     linux.price = 0.01 ;
    cout << " It costs less than $" << linux.price ;
 
    linux.devs = 1200 ;
    cout << " and has about " << linux.devs << "
    developers on each release!" << endl << endl ;
 
    union opSysName windows = {"restrictive, proprietary and monopolistic!"} ;
 
    cout << "A certain other consumer OS is generally
    " << windows.desc ;
 
    windows.price = 99.99 ;
 
    cout << " It costs too much, i.e £" << windows.price ;
 
    windows.devs = 1138 ;
 
  
     cout << ", and has around " << windows.devs << " developers trying to make it work!" ;
 
    return 0;
}

Compile & Run:

The best OS might just possibly be fun, free and better! It costs less than $0.01 and has about 1200 developers on each release!
                
A certain other consumer OS is generally restrictive, proprietary and monopolistic! It costs too much, i.e £99.99, and has around 1138 developers trying to make it work!

Source: Derrick Robinson, http://cpp.tech-academy.co.uk/unions/
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