What is the size of an enum in C

Question

I m creating a set of enum values  but I need each enum value to be 64 bits wide  If I recall correctly  an enum is generally the same size as an int  but I thought I read somewhere that  at least in GCC  the compiler can make the enum any width they need to be to hold their values  So  is it possible to have an enum that is 64 bits wide

User · Accepted Answer

An enum is only guaranteed to be large enough to hold int values   The compiler is free to choose the actual type used based on the enumeration constants defined so it can choose a smaller type if it can represent the values you define   If you need enumeration constants that don t fit into an int you will need to use compiler-specific extensions to do so

User · Answer

In C language  an enum is guaranteed to be of size of an int  There is a compile time option  -fshort-enums  to make it as short  This is mainly useful in case the values are not more than 64K   There is no compile time option to increase its size to 64 bit

User · Answer

Taken from the current C Standard  C99   http   www open-std org JTC1 SC22 WG14 www docs n1256 pdf  6 7 2 2 Enumeration specifiers       Constraints The expression that defines the value of an enumeration constant shall be an integer constant expression that has a value representable as an int        Each enumerated type shall be compatible with char  a signed integer type  or an unsigned integer type  The choice of type is implementation-defined  but shall be capable of representing the values of all the members of the enumeration   Not that compilers are any good at following the standard  but essentially  If your enum holds anything else than an int  you re in deep  quot unsupported behavior that may come back biting you in a year or two quot  territory  Update  The latest publicly available draft of the C Standard  C11   http   www open-std org JTC1 SC22 WG14 www docs n1570 pdf contains the same clauses  Hence  this answer still holds for C11

User · Answer

Consider this code   enum value a b c d e f g h i j l m n   value s  cout  lt  lt  sizeof s   lt  lt  endl    It will give 4 as output  So no matter the number of elements an enum contains  its size is always fixed

User · Answer

Just set the last value of the enum to a value large enough to make it the size you would like the enum to be  it should then be that size   enum value a 0 b c d e f g h i j l m n last 0xFFFFFFFFFFFFFFFF

User · Answer

Just set the last value of the enum to a value large enough to make it the size you would like the enum to be  it should then be that size   enum value a 0 b c d e f g h i j l m n last 0xFFFFFFFFFFFFFFFF

User · Answer

In C language  an enum is guaranteed to be of size of an int  There is a compile time option  -fshort-enums  to make it as short  This is mainly useful in case the values are not more than 64K   There is no compile time option to increase its size to 64 bit

User · Answer

Consider this code   enum value a b c d e f g h i j l m n   value s  cout  lt  lt  sizeof s   lt  lt  endl    It will give 4 as output  So no matter the number of elements an enum contains  its size is always fixed

User · Answer

Taken from the current C Standard  C99   http   www open-std org JTC1 SC22 WG14 www docs n1256 pdf  6 7 2 2 Enumeration specifiers       Constraints The expression that defines the value of an enumeration constant shall be an integer constant expression that has a value representable as an int        Each enumerated type shall be compatible with char  a signed integer type  or an unsigned integer type  The choice of type is implementation-defined  but shall be capable of representing the values of all the members of the enumeration   Not that compilers are any good at following the standard  but essentially  If your enum holds anything else than an int  you re in deep  quot unsupported behavior that may come back biting you in a year or two quot  territory  Update  The latest publicly available draft of the C Standard  C11   http   www open-std org JTC1 SC22 WG14 www docs n1570 pdf contains the same clauses  Hence  this answer still holds for C11

User · Answer

Taken from the current C Standard  C99   http   www open-std org JTC1 SC22 WG14 www docs n1256 pdf  6 7 2 2 Enumeration specifiers       Constraints The expression that defines the value of an enumeration constant shall be an integer constant expression that has a value representable as an int        Each enumerated type shall be compatible with char  a signed integer type  or an unsigned integer type  The choice of type is implementation-defined  but shall be capable of representing the values of all the members of the enumeration   Not that compilers are any good at following the standard  but essentially  If your enum holds anything else than an int  you re in deep  quot unsupported behavior that may come back biting you in a year or two quot  territory  Update  The latest publicly available draft of the C Standard  C11   http   www open-std org JTC1 SC22 WG14 www docs n1570 pdf contains the same clauses  Hence  this answer still holds for C11

User · Answer

We have no control over the size of an enum variable  It totally depends on the implementation  and the compiler gives the option to store a name for an integer using enum  so enum is following the size of an integer

User · Answer

Taken from the current C Standard  C99   http   www open-std org JTC1 SC22 WG14 www docs n1256 pdf  6 7 2 2 Enumeration specifiers       Constraints The expression that defines the value of an enumeration constant shall be an integer constant expression that has a value representable as an int        Each enumerated type shall be compatible with char  a signed integer type  or an unsigned integer type  The choice of type is implementation-defined  but shall be capable of representing the values of all the members of the enumeration   Not that compilers are any good at following the standard  but essentially  If your enum holds anything else than an int  you re in deep  quot unsupported behavior that may come back biting you in a year or two quot  territory  Update  The latest publicly available draft of the C Standard  C11   http   www open-std org JTC1 SC22 WG14 www docs n1570 pdf contains the same clauses  Hence  this answer still holds for C11

User · Answer

While the previous answers are correct  some compilers have options to break the standard and use the smallest type that will contain all values   Example with GCC  documentation in the GCC Manual    enum ord       FIRST   1      SECOND      THIRD     attribute       packed      STATIC ASSERT  sizeof enum ord     1

User · Answer

We have no control over the size of an enum variable  It totally depends on the implementation  and the compiler gives the option to store a name for an integer using enum  so enum is following the size of an integer

User · Answer

While the previous answers are correct  some compilers have options to break the standard and use the smallest type that will contain all values   Example with GCC  documentation in the GCC Manual    enum ord       FIRST   1      SECOND      THIRD     attribute       packed      STATIC ASSERT  sizeof enum ord     1

[c] What is the size of an enum in C?

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