gdb provides the following ways to control how arrays, structures,
and symbols are printed.
These settings are useful for debugging programs in any language:
set print address, set print address on
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<listitem>GDBN'} prints memory addresses showing the location of stack
traces, structure values, pointer values, breakpoints, and so forth,
even when it also displays the contents of those addresses. The default
is on. For example, this is what a stack frame display looks like with
set print address on:
(gdb) f
#0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
at input.c:530
530 if (lquote != def_lquote)
set print address off
Do not print addresses when displaying their contents. For example,
this is the same stack frame displayed with set print address off:
(gdb) set print addr off
(gdb) f
#0 set_quotes (lq="<<", rq=">>") at input.c:530
530 if (lquote != def_lquote)
You can use set print address off to eliminate all machine
dependent displays from the gdb interface. For example, with
print address off, you should get the same text for backtraces on
all machines--whether or not they involve pointer arguments.
show print address
Show whether or not addresses are to be printed.
When gdb prints a symbolic address, it normally prints the
closest earlier symbol plus an offset. If that symbol does not uniquely
identify the address (for example, it is a name whose scope is a single
source file), you may need to clarify. One way to do this is with
info line, for example info line *0x4537. Alternately,
you can set gdb to print the source file and line number when
it prints a symbolic address:
set print symbol-filename on
Tell gdb to print the source file name and line number of a
symbol in the symbolic form of an address.
set print symbol-filename off
Do not print source file name and line number of a symbol. This is the
default.
show print symbol-filename
Show whether or not gdb will print the source file name and
line number of a symbol in the symbolic form of an address.
Another situation where it is helpful to show symbol filenames and line
numbers is when disassembling code; gdb shows you the line
number and source file that corresponds to each instruction.
Also, you may wish to see the symbolic form only if the address being
printed is reasonably close to the closest earlier symbol:
set print max-symbolic-offset max-offset
Tell gdb to only display the symbolic form of an address if the
offset between the closest earlier symbol and the address is less than
max-offset. The default is 0, which tells gdb
to always print the symbolic form of an address if any symbol precedes it.
show print max-symbolic-offset
Ask how large the maximum offset is that gdb prints in a
symbolic address.
If you have a pointer and you are not sure where it points, try
set print symbol-filename on. Then you can determine the name
and source file location of the variable where it points, using
p/a pointer. This interprets the address in symbolic form.
For example, here gdb shows that a variable ptt points
at another variable t, defined in hi2.c:
(gdb) set print symbol-filename on
(gdb) p/a ptt
$4 = 0xe008 <t in hi2.c>
Warning: For pointers that point to a local variable, p/a
does not show the symbol name and filename of the referent, even with
the appropriate set print options turned on.
Other settings control how different kinds of objects are printed:
set print array, set print array on
Pretty print arrays. This format is more convenient to read,
but uses more space. The default is off.
set print array off
Return to compressed format for arrays.
show print array
Show whether compressed or pretty format is selected for displaying
arrays.
set print elements number-of-elements
Set a limit on how many elements of an array gdb will print.
If gdb is printing a large array, it stops printing after it has
printed the number of elements set by the set print elements command.
This limit also applies to the display of strings.
When gdb starts, this limit is set to 200.
Setting number-of-elements to zero means that the printing is unlimited.
show print elements
Display the number of elements of a large array that gdb will print.
If the number is 0, then the printing is unlimited.
set print null-stop
Cause gdb to stop printing the characters of an array when the first
null is encountered. This is useful when large arrays actually
contain only short strings.
The default is off.
set print pretty on
Cause gdb to print structures in an indented format with one member
per line, like this:
Show which format gdb is using to print structures.
set print sevenbit-strings on
Print using only seven-bit characters; if this option is set,
gdb displays any eight-bit characters (in strings or
character values) using the notation \nnn. This setting is
best if you are working in English (ascii) and you use the
high-order bit of characters as a marker or "meta" bit.
set print sevenbit-strings off
Print full eight-bit characters. This allows the use of more
international character sets, and is the default.
show print sevenbit-strings
Show whether or not gdb is printing only seven-bit characters.
set print union on
Tell gdb to print unions which are contained in structures. This
is the default setting.
set print union off
Tell gdb not to print unions which are contained in structures.
show print union
Ask gdb whether or not it will print unions which are contained in
structures.
and with set print union off in effect it would print
$1 = {it = Tree, form = {...}}
These settings are of interest when debugging C++ programs:
set print demangle, set print demangle on
Print C++ names in their source form rather than in the encoded
("mangled") form passed to the assembler and linker for type-safe
linkage. The default is on.
show print demangle
Show whether C++ names are printed in mangled or demangled form.
set print asm-demangle, set print asm-demangle on
Print C++ names in their source form rather than their mangled form, even
in assembler code printouts such as instruction disassemblies.
The default is off.
show print asm-demangle
Show whether C++ names in assembly listings are printed in mangled
or demangled form.
set demangle-style style
Choose among several encoding schemes used by different compilers to
represent C++ names. The choices for style are currently:
auto
Allow gdb to choose a decoding style by inspecting your program.
gnu
Decode based on the gnu C++ compiler (g++) encoding algorithm.
This is the default.
hp
Decode based on the HP ANSI C++ (aCC) encoding algorithm.
lucid
Decode based on the Lucid C++ compiler (lcc) encoding algorithm.
arm
Decode using the algorithm in the [C++ Annotated Reference Manual].
Warning: this setting alone is not sufficient to allow
debugging cfront-generated executables. gdb would
require further enhancement to permit that.
If you omit style, you will see a list of possible formats.
show demangle-style
Display the encoding style currently in use for decoding C++ symbols.
set print object, set print object on
When displaying a pointer to an object, identify the actual
(derived) type of the object rather than the declared type, using
the virtual function table.
set print object off
Display only the declared type of objects, without reference to the
virtual function table. This is the default setting.
show print object
Show whether actual, or declared, object types are displayed.
set print static-members, set print static-members on
Print static members when displaying a C++ object. The default is on.
set print static-members off
Do not print static members when displaying a C++ object.
show print static-members
Show whether C++ static members are printed, or not.
set print vtbl, set print vtbl on
Pretty print C++ virtual function tables. The default is off.
(The vtbl commands do not work on programs compiled with the HP
ANSI C++ compiler (aCC).)
set print vtbl off
Do not pretty print C++ virtual function tables.
show print vtbl
Show whether C++ virtual function tables are pretty printed, or not.
