what is the size of an enum type data in C

Question

This is a C   interview test question not homework     include  lt iostream gt  using namespace std  enum months t   january  february  march  april  may  june  july  august  september        october  november  december  y2k    int main            cout  lt  lt   sizeof months t is     lt  lt  sizeof months t   lt  lt  endl      cout  lt  lt   sizeof y2k is     lt  lt  sizeof y2k   lt  lt  endl      enum months t1   january  february  march  april  may  june  july  august             september  october  november  december  y2k1      cout  lt  lt   sizeof months t1 is     lt  lt  sizeof months t1   lt  lt  endl      cout  lt  lt   sizeof y2k1 is     lt  lt  sizeof y2k1   lt  lt  endl       Output      sizeof months t is  4   sizeof y2k is  4   sizeof months t1 is  4   sizeof y2k1 is  4     Why is the size of all of these 4 bytes  Not 12 x 4   48 bytes  I know union elements occupy the same memory location  but this is an enum

User · Answer

This is a C   interview test question not homework     Then your interviewer needs to refresh his recollection with how the C   standard works  And I quote      For an enumeration whose underlying type is not fixed  the underlying type is an integral type that can represent all the enumerator values defined in the enumeration    The whole  whose underlying type is not fixed  part is from C  11  but the rest is all standard C  98 03  In short  the sizeof months t  is not 4  It is not 2 either  It could be any of those  The standard does not say what size it should be  only that it should be big enough to fit any enumerator      why the all size is 4 bytes   not 12 x 4   48 bytes     Because enums are not variables  The members of an enum are not actual variables  they re just a semi-type-safe form of  define  They re a way of storing a number in a reader-friendly format  The compiler will transform all uses of an enumerator into the actual numerical value   Enumerators are just another way of talking about a number  january is just shorthand for 0  And how much space does 0 take up  It depends on what you store it in

User · Answer

An enum is kind of like a typedef for the int type  kind of    So the type you ve defined there has 12 possible values  however a single variable only ever has one of those values   Think of it this way  when you define an enum you re basically defining another way to assign an int value   In the example you ve provided  january is another way of saying 0  feb is another way of saying 1  etc until december is another way of saying 11

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Because it s the size of an instance of the type - presumably enum values are stored as  32-bit   4-byte  ints here

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I like the explanation From EdX  Microsoft  DEV210x Introduction to C    for a similar problem    The enum represents the literal values of days as integers  Referring to the numeric types table  you see that an int takes 4 bytes of memory  7 days x 4 bytes each would require 28 bytes of memory if the entire enum were stored but the compiler only uses a single element of the enum  therefore the size in memory is actually 4 bytes

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An enum is nearly an integer  To simplify a lot  enum yourenum   a  b  c      is almost like   define a 0  define b 1  define c 2   Of course  it is not really true  I m trying to explain that enum are some kind of coding

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With my now ageing Borland C   Builder compiler enums can be 1 2 or 4 bytes  although it does have a flag you can flip to force it to use ints   I guess it s compiler specific

User · Answer

It depends  The standard only demands that it is large enough to hold all values  so formally an enum like enum foo   zero  one  two    needs to only be one byte large  However most implementations make those enums as large as ints  that s faster on modern hardware  moreover it s needed for compatibility with C where enums are basically glorified ints   Note however that C   allows enums with initializers outside of the int range  and for those enums the size will of course also be larger  For example  if you have enum bar   a  b   1LL  lt  lt  35    then your enum will be larger than 32 bits  most likely 64 bits  even on a system with 32 bit ints  note that in C that enum would not be allowed

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The size is four bytes because the enum is stored as an int  With only 12 values  you really only need 4 bits  but 32 bit machines process 32 bit quantities more efficiently than smaller quantities   0 0 0 0  January 0 0 0 1  February 0 0 1 0  March 0 0 1 1  April 0 1 0 0  May 0 1 0 1  June 0 1 1 0  July 0 1 1 1  August 1 0 0 0  September 1 0 0 1  October 1 0 1 0  November 1 0 1 1  December 1 1 0 0     unused    1 1 0 1     unused    1 1 1 0     unused    1 1 1 1     unused      Without enums  you might be tempted to use raw integers to represent the months  That would work and be efficient  but it would make your code hard to read  With enums  you get efficient storage and readability

[c++] what is the size of an enum type data in C++?

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