Union

• Union ये एक अलग-अलग data types का collection होता है |
• अगर union का इस्तेमाल करना हो तो 'union' keyword का इस्तेमाल करते है |
• Union ये structure के जैसा ही होता है |
• Union में किये हुए हर variable के decaration को 'member' कहते है |
• Union हर एक member के लिए अलग-अलग memory allocate नहीं करता है |
• Union के members एक ही memory location को share करते है |
• Union में जो member अपने size में बड़ा होता है, तो वो पूरे Union की size होती है |

Syntax Difference between Structure and Union Defintion

Syntax for Structure Definition

struct structure_name{  

    data_type member 1;  
    data_type member 2;  
    ------------------
    ------------------
    data_type memeber n;  
};  

Syntax for Union Definition

struct union_name{  

    data_type member 1;  
    data_type member 2;  
    ------------------
    ------------------
    data_type memeber n;  
};  

Syntax में सिर्फ struct और union keyword में फर्क है | Structure के members अलग-अलग memory allocate करते है | Union के members एक ही member की memory पर store होते है |

Example for Structure Definition

struct Employee{
    int emp_id;
    char emp_name[30];
}; 

Example for Union Definition

union Student{
    int stud_id;
    char stud_name[30];
};

Memory Representation

	Structure			Union
Structure_name	Employee			Student
Member_name	emp_id	emp_name[30]		stud_id and stud_name[30]		Location
Memory Address	6356728	6356732		6356762
Member Size	4bytes	30bytes		4bytes	30bytes
Total Size	34bytes			30bytes

Union Variable Declaration

Structure का variable declare करने के दो प्रकार है |

1. जब Union की definition लिखी जाती तब वहा पर भी Structure variable को लिखा जाता है |
2. Union के variable को main() function के अंदर भी किया जाता है |

Syntax for Union Variable outside of Union Definition

struct Union_name{  

    data_type member 1;  
    data_type member 2;  
    ------------------
    ------------------
    data_type memeber n;  
}Union_variable(s);  

Example for Union Variable in main() Function

struct Employee{
    int emp_id;
    char emp_name[30];
    float salary;
}info;

Syntax for Union Variable in main() Function

union Union_name{  

    data_type member 1;  
    data_type member 2;  
    ------------------
    ------------------
    data_type memeber n;  
}Union_variable(s);
int main(){
 union Union_name Union_variable_name;
}  

Example for Union Variable in main() Function

union Employee{
    int emp_id;
    char emp_name[30];
    float salary;
};
int main(){
 union Employee info;
} 

Full Example for Union

Source Code :

#include <stdio.h>
#include <string.h>

union Employee {
    int emp_id;
    char emp_name[30];
    float salary;
}info;

int main(){

    info.emp_id = 34;
    strcpy( info.emp_name, "Raj Biradar");
    info.salary = 20000.00;

    printf( "Employee id is : %d\n", info.emp_id);
    printf( "Employee name is %s\n", info.emp_name);
    printf( "Employee salary is : %f", info.salary);

return 0;
}

Output :

Employee id is : 1184645120
Employee name is
Employee salary is : 20000.000000

Union working with size(sizeof)

Union के member एक ही memory location में store होता है और पूरे Union का size जो सबसे बड़ा member होता है, वो size Union की होती है |
Source Code :

#include <stdio.h>
#include <string.h>

union Employee {
    int emp_id;
    char emp_name[20];
    float salary;
};
int main(){
 union Employee info;

    printf( "Size of Employee id is : %d bytes\n", sizeof(info.emp_id));  // size of emp_id
    printf( "Size of Employee name : %d bytes\n", sizeof(info.emp_name)); // size of emp_name
    printf( "Size of Employee salary is : %d bytes\n", sizeof(info.salary)); // size of salary
    printf( "Size of Employee union : %d bytes", sizeof(info)); // size of Employee

return 0;
}

Ouutput :

Size of Employee id is : 4 bytes
Size of Employee name : 20 bytes
Size of Employee salary is : 4 bytes
Size of Employee union : 20 bytes

Union using Pointer

Union के Members को दो प्रकार से access किया जाता है |

1. . (dot Operator)
2. -> (pointer Operator)

Accessing Members using pointer Operator

Source Code :

#include <stdio.h>
#include <string.h>

union Employee {
    int  emp_id;
    char  emp_name[30];
    float  salary;
};
int main(){
 union Employee info;
 union Employee *ptr;

 ptr = &info;

    ptr->emp_id = 34;
    strcpy( ptr->emp_name, "Raj Biradar");
    ptr->salary = 20000.00;

    printf( "Employee id is : %d\n", ptr->emp_id);
    printf( "Employee name is %s\n", ptr->emp_name);
    printf( "Employee salary is : %f", ptr->salary);

return 0;
}

< /pre>

Output :

Employee id is : 1184645120
Employee name is
Employee salary is : 20000.000000