5.7 Enumerations

Enumerations are defined with the ‘e’ type descriptor.

The source line below declares an enumeration type at file scope. The type definition is located after the N_RBRAC that marks the end of the previous procedure’s block scope, and before the N_FUN that marks the beginning of the next procedure’s block scope. Therefore it does not describe a block local symbol, but a file local one.

The source line:

enum e_places {first,second=3,last};

generates the following stab:

.stabs "e_places:T22=efirst:0,second:3,last:4,;",128,0,0,0

The symbol descriptor (‘T’) says that the stab describes a structure, enumeration, or union tag. The type descriptor ‘e’, following the ‘22=’ of the type definition narrows it down to an enumeration type. Following the ‘e’ is a list of the elements of the enumeration. The format is ‘name:value,’. The list of elements ends with ‘;’. The fact that value is specified as an integer can cause problems if the value is large. GCC 2.5.2 tries to output it in octal in that case with a leading zero, which is probably a good thing, although GDB 4.11 supports octal only in cases where decimal is perfectly good. Negative decimal values are supported by both GDB and dbx.

There is no standard way to specify the size of an enumeration type; it is determined by the architecture (normally all enumerations types are 32 bits). Type attributes can be used to specify an enumeration type of another size for debuggers which support them; see The String Field.

Enumeration types are unusual in that they define symbols for the enumeration values (first, second, and third in the above example), and even though these symbols are visible in the file as a whole (rather than being in a more local namespace like structure member names), they are defined in the type definition for the enumeration type rather than each having their own symbol. In order to be fast, GDB will only get symbols from such types (in its initial scan of the stabs) if the type is the first thing defined after a ‘T’ or ‘t’ symbol descriptor (the above example fulfills this requirement). If the type does not have a name, the compiler should emit it in a nameless stab (see The String Field); GCC does this.