packed

This attribute, attached to an enum, struct, or union type definition, specified that the minimum required memory be used to represent the type.

Specifying this attribute for struct and union types is equivalent to specifying the packed attribute on each of the structure or union members. Specifying the '-fshort-enums' flag on the line is equivalent to specifying the packed attribute on all enum definitions.

You may only specify this attribute after a closing curly brace on an enum definition, not in a typedef declaration, unless that declaration also contains the definition of the enum.