Union in C programming

Union in C programming

• 1.
  Union
• 2.
  • A unionis declared using the keyword union as: union student { char name[20]; int roll_no; float marks; char section; }; union student s; • While accessing union members, we should make sure that we are accessing the member whose value is currently residing in the memory. Otherwise we will get erroneous output (which is machine dependent). 2
• 3.
  Unions: • A unionis a variable that may hold (at different times) objects of different types and sizes, with the compiler keeping track of size and alignment requirements. • Unions provide a way to manipulate different kinds of data in a single area of storage, without embedding any machine-dependent information in the program. • Both structure and unions are used to group a number of different variables together. Syntactically both structure and unions are exactly same. The main difference between them is in storage. • In structures, each member has its own memory location but all members of union use the same memory location which is equal to the greatest member’s size. 3
• 4.
  Example: program illustratesthe structure in which read member elements of union and display them. #include<stdio.h> union Student { char name[20]; int roll; char sec; F loat marks; }; union Student s1; void main() { printf(“Enter the name of a student”); gets(s1.name); printf(“Enter the roll number of a student”); scanf(“%d”,&s1.roll); printf(“Enter the section of a student”); scanf(“%c”,&s1.sec); printf(“Enter the marks obtained by the student”); scanf(“%f”,&s1.marks); /displaying the records printf(“Name=%sn Roll number =%dn Section=%cn Obtained marks=%f”,s1.name, s1.roll, s1.sec, s1.marks); } 4
• 5.
  Example: union student { char name[20]; introll_no; float marks; char section; }; void main() { union student s; clrscr(); printf("Size of union=%dn", sizeof(s)); strcpy(s.name, “cnr"); printf("Name=%st", s.name); printf("Location=%u", s.name); s.roll_no=10; printf("nRoll=%d tLocation=%u", s.roll_no, &s.roll_no); s.marks=91.5; printf("nMarks=%.2f tLocation=%u", s.marks, &s.marks); s.section='A'; printf("nSection=%c tLocation=%u", s.section, &s.section); printf("nnErroneous output"); printf("nnNametRolltMarkstSectionn"); printf("%st%dt%.2ft%c", s.name, s.roll_no, s.marks, s.section); getch(); } 5