Locating Symbols

In a program, the same name may refer to different types of program entities and occur in many scopes. The dbx whereis command lists the fully qualified name--hence, the location--of all symbols of that name. The dbx which command tells you which occurrence of a symbol dbx uses if you give that name as the target of a debugging command.

Printing a List of Occurrences of a Symbol

To print a list of all the occurrences of a specified symbol, use the whereis symbol, where symbol can be any user-defined identifier. For example:

(dbx) whereis table
forward: `Blocks`block_draw.cc`table
function: `Blocks`block.cc`table::table(char*, int, int, const point&)
class: `Blocks`block.cc`table
class: `Blocks`main.cc`table
variable:       `libc.so.1`hsearch.c`table

The output includes the name of the loadable object(s) where the program defines symbol, as well as the kind of entity each object is: class, function, or variable.

Because information from the dbx symbol table is read in as it is needed, the whereis command knows only about occurrences of a symbol that are already loaded. As a debugging session gets longer, the list of occurrences may grow.

Determining Which Symbol dbx Uses

The which command tells you which symbol with a given name it uses if you specify that name (without fully qualifying it) as the target of a debugging command. For example:

(dbx) func
wedge::wedge(char*, int, int, const point&, load_bearing_block*)
(dbx) which draw
`block_draw.cc`wedge::draw(unsigned long)

If a specified symbol name is not in a local scope, the which command searches for the first occurrence of the symbol along the scope resolution search path. If which finds the name, it reports the fully qualified name.

If, at any place along the search path the search finds multiple occurrences of symbol at the same scope level, dbx prints a message in the command pane reporting the ambiguity:

(dbx) which fid
`example`file1.c`fid
`example`file2.c`fid

dbx shows the overload display, listing the ambiguous symbols names. In the context of the which command, choosing from the list of occurrences does not affect the state of dbx or the program. Whichever occurrence you choose, dbx merely echoes the name.

Remember that the which command gives you a preview of what happens if you make symbol (in this example, block) an argument of a command that must operate on symbol (for example, a print command). In the case of ambiguous names, the overload display list indicates that dbx does not yet know which occurrence of two or more names it uses. dbx lists the possibilities and waits for you to choose one.