Union

• Unions are C variables whose syntax look similar to structures, but act in a completely different manner. 

• Once a union variable has been declared, the amount of memory reserved is just enough to be able to represent the largest member. (Unlike a structure where memory is reserved for all members). 

• Data actually stored in a union’s memory can be the data associated with any of its members. 

• But only one member of a union can contain valid data at a given point in the program. 

• It is the user’s responsibility to keep track of which type of data has most recently been stored in the union variable. 

Example :

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#include <stdio.h> #include <string.h> union Data{ int i; float f; char str[20]; }; int main( ){ union Data d1; d1.i = 10; d1.f = 220.5; strcpy(d1.str,"Embedded C"); printf( "d1.i : %d\n", d1.i); printf( "d1.f : %f\n", d1.f); printf( "d1.str : %s\n", d1.str); printf("Union size : %d199 bytes",sizeof(d1)); return 0; }

Output :

d1.i : 1700949317
d1.f : 66829405762910173528064.000000
d1.str : Embedded C

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