GDB can fill in the rest of a word in a command for you, if there is only one possibility; it can also show you what the valid possibilities are for the next word in a command, at any time. This works for GDB commands, GDB subcommands, and the names of symbols in your program.
Press the TAB key whenever you want GDB to fill out the rest of a word. If there is only one possibility, GDB fills in the word, and waits for you to finish the command (or press RET to enter it). For example, if you type
(gdb) info bre TAB
GDB fills in the rest of the word `breakpoints', since that is
the only info subcommand beginning with `bre':
(gdb) info breakpoints
You can either press RET at this point, to run the info
breakpoints command, or backspace and enter something else, if
`breakpoints' does not look like the command you expected. (If you
were sure you wanted info breakpoints in the first place, you
might as well just type RET immediately after `info bre',
to exploit command abbreviations rather than command completion).
If there is more than one possibility for the next word when you press TAB, GDB sounds a bell. You can either supply more characters and try again, or just press TAB a second time; GDB displays all the possible completions for that word. For example, you might want to set a breakpoint on a subroutine whose name begins with `make_', but when you type b make_TAB GDB just sounds the bell. Typing TAB again displays all the function names in your program that begin with those characters, for example:
(gdb) b make_ TAB GDB sounds bell; press TAB again, to see: make_a_section_from_file make_environ make_abs_section make_function_type make_blockvector make_pointer_type make_cleanup make_reference_type make_command make_symbol_completion_list (gdb) b make_
After displaying the available possibilities, GDB copies your partial input (`b make_' in the example) so you can finish the command.
If you just want to see the list of alternatives in the first place, you can press M-? rather than pressing TAB twice. M-? means META ?. You can type this either by holding down a key designated as the META shift on your keyboard (if there is one) while typing ?, or as ESC followed by ?.
Sometimes the string you need, while logically a "word", may contain
parentheses or other characters that GDB normally excludes from
its notion of a word. To permit word completion to work in this
situation, you may enclose words in ' (single quote marks) in
GDB commands.
The most likely situation where you might need this is in typing the
name of a C++ function. This is because C++ allows function
overloading (multiple definitions of the same function, distinguished
by argument type). For example, when you want to set a breakpoint you
may need to distinguish whether you mean the version of name
that takes an int parameter, name(int), or the version
that takes a float parameter, name(float). To use the
word-completion facilities in this situation, type a single quote
' at the beginning of the function name. This alerts
GDB that it may need to consider more information than usual
when you press TAB or M-? to request word completion:
(gdb) b 'bubble( M-? bubble(double,double) bubble(int,int) (gdb) b 'bubble(
In some cases, GDB can tell that completing a name requires using quotes. When this happens, GDB inserts the quote for you (while completing as much as it can) if you do not type the quote in the first place:
(gdb) b bub TAB GDB alters your input line to the following, and rings a bell: (gdb) b 'bubble(
In general, GDB can tell that a quote is needed (and inserts it) if you have not yet started typing the argument list when you ask for completion on an overloaded symbol.
For more information about overloaded functions, see section C++ expressions. You can use the command set
overload-resolution off to disable overload resolution;
see section GDB features for C++.
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