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Oct 31, 2008 · union are used to save memory, especially used on devices with limited memory where memory is important. Exp: union _Union{ int a; double b; char c; }; For example,let's say we need the above 3 data types(int,double,char) in a system where memory is limited.If we don't use "union",we need to define these 3 data types.
Feb 22, 2010 · The purpose of unions is rather obvious, but for some reason people miss it quite often. The purpose of union is to save memory by using the same memory region for storing different objects at different times. That's it. It is like a room in a hotel. Different people live in it for non-overlapping periods of time.
Dec 6, 2008 · The uses of union Unions are used frequently when specialized type conversations are needed. To get an idea of the usefulness of union. The c/c standard library defines no function specifically designed to write short integers to a file. Using fwrite() incurs encurs excessive overhead for simple operation.
Dec 23, 2013 · 28. Use w->member->type. You need to allocate the union specifically. One note that may be a point of misunderstanding is that the union holds EITHER the int, or TYPEA, or TYPEB, so in particular you cannot rely on your int type; in the union to tell you which struct the union holds.
Type type; union {. int integer; char *string; float real; void *pointer; } x; Using this you can write code that handles "values" without knowing their exact type, for instance implement a stack and so on. Since this is in (old, pre-C11) C, the inner union must be given a field name in the outer struct.
Apr 26, 2017 · I think you misunderstand what a union is then. only one field may be (safely) used at a time. if you want to be able to access both fields, you need a struct. if you just want to make sure the whole damn thing is nulled out, you can pick either one in this case, since the pointer types (probably) have the same length.
Aug 15, 2012 · The smallest unit that is addressable in C is always a byte (called char in C). You cannot access a bit directly. The closest way to get to accessing bits would be to define a data type called bitpointer and define some functions or macros for it: #include <stdbool.h>. typedef struct bitpointer {.
Aug 15, 2012 · In C/C++ union is used to overlay different members in the same memory location, so if you have a union of an int and a float they both use the same 4 bytes of memory to store, obviously writing to one corrupts the other (since int and float have different bit layout). In .Net Microsoft went with the safer choice and didn't include this feature.
Oct 23, 2010 · 1. Most answers here are correct. A union is essentially a way to access same data in different ways (For example, you can access/interpret 4 bytes of memory as 1 integers, or as 4 characters). Structs as you know are straightforward - a collection of different, seprate objects with their own memory.
Mar 1, 2016 · So using bitfields in union, as you have written above, is perfectly valid C but a useless piece of code. All the fields inside union share same memory so all the bitfields you mention are essentially same flag as they share same memory. This metaphor is far more useless than the code in the OP's question.
