### 5.3 Cross-References to Other Types

A type can be used before it is defined; one common way to deal with that situation is just to use a type reference to a type which has not yet been defined.

Another way is with the ‘`x`’ type descriptor, which is followed by ‘`s`’ for a structure tag, ‘`u`’ for a union tag, or ‘`e`’ for a enumerator tag, followed by the name of the tag, followed by ‘`:`’. If the name contains ‘`::`’ between a ‘`<`’ and ‘`>`’ pair (for C`++` templates), such a ‘`::`’ does not end the name—only a single ‘`:`’ ends the name; see Nested Symbols.

For example, the following C declarations:

    struct foo;
    struct foo *bar;

produce:

    .stabs "bar:G16=*17=xsfoo:",32,0,0,0

Not all debuggers support the ‘`x`’ type descriptor, so on some machines GCC does not use it. I believe that for the above example it would just emit a reference to type 17 and never define it, but I haven’t verified that.

Modula-2 imported types, at least on AIX, use the ‘`i`’ type descriptor, which is followed by the name of the module from which the type is imported, followed by ‘`:`’, followed by the name of the type. There is then optionally a comma followed by type information for the type. This differs from merely naming the type (see Typedefs) in that it identifies the module; I don’t understand whether the name of the type given here is always just the same as the name we are giving it, or whether this type descriptor is used with a nameless stab (see String Field), or what. The symbol ends with ‘`;`’.