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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 addressset print address onGDB 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 offDo 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 addressShow 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 onTell GDB to print the source file name and line number of a symbol in the symbolic form of an address.
set print symbol-filename offDo not print source file name and line number of a symbol. This is the default.
show print symbol-filenameShow 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-offsetset print max-symbolic-offset unlimitedTell 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 unlimited, which tells GDB
to always print the symbolic form of an address if any symbol precedes
it. Zero is equivalent to unlimited.
show print max-symbolic-offsetAsk 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 printoptions turned on.
You can also enable ‘/a’-like formatting all the time using ‘set print symbol on’:
set print symbol onTell GDB to print the symbol corresponding to an address, if one exists.
set print symbol offTell GDB not to print the symbol corresponding to an address. In this mode, GDB will still print the symbol corresponding to pointers to functions. This is the default.
show print symbolShow whether GDB will display the symbol corresponding to an address.
Other settings control how different kinds of objects are printed:
set print arrayset print array onPretty print arrays. This format is more convenient to read, but uses more space. The default is off.
set print array offReturn to compressed format for arrays.
show print arrayShow whether compressed or pretty format is selected for displaying arrays.
set print array-indexesset print array-indexes onPrint the index of each element when displaying arrays. May be more convenient to locate a given element in the array or quickly find the index of a given element in that printed array. The default is off.
set print array-indexes offStop printing element indexes when displaying arrays.
show print array-indexesShow whether the index of each element is printed when displaying arrays.
set print elements number-of-elementsset print elements unlimitedSet 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 unlimited or zero means
that the number of elements to print is unlimited.
show print elementsDisplay the number of elements of a large array that GDB will print. If the number is 0, then the printing is unlimited.
set print frame-arguments valueThis command allows to control how the values of arguments are printed when the debugger prints a frame (see Frames). The possible values are:
allThe values of all arguments are printed.
scalarsPrint the value of an argument only if it is a scalar. The value of more
complex arguments such as arrays, structures, unions, etc, is replaced
by …. This is the default. Here is an example where
only scalar arguments are shown:
#1 0x08048361 in call_me (i=3, s=…, ss=0xbf8d508c, u=…, e=green) at frame-args.c:23
noneNone of the argument values are printed. Instead, the value of each argument
is replaced by …. In this case, the example above now becomes:
#1 0x08048361 in call_me (i=…, s=…, ss=…, u=…, e=…) at frame-args.c:23
By default, only scalar arguments are printed. This command can be used
to configure the debugger to print the value of all arguments, regardless
of their type. However, it is often advantageous to not print the value
of more complex parameters. For instance, it reduces the amount of
information printed in each frame, making the backtrace more readable.
Also, it improves performance when displaying Ada frames, because
the computation of large arguments can sometimes be CPU-intensive,
especially in large applications. Setting print frame-arguments
to scalars (the default) or none avoids this computation,
thus speeding up the display of each Ada frame.
show print frame-argumentsShow how the value of arguments should be displayed when printing a frame.
set print raw frame-arguments onPrint frame arguments in raw, non pretty-printed, form.
set print raw frame-arguments offPrint frame arguments in pretty-printed form, if there is a pretty-printer for the value (see Pretty Printing), otherwise print the value in raw form. This is the default.
show print raw frame-argumentsShow whether to print frame arguments in raw form.
set print entry-values valueSet printing of frame argument values at function entry. In some cases GDB can determine the value of function argument which was passed by the function caller, even if the value was modified inside the called function and therefore is different. With optimized code, the current value could be unavailable, but the entry value may still be known.
The default value is default (see below for its description). Older
GDB behaved as with the setting no. Compilers not supporting
this feature will behave in the default setting the same way as with the
no setting.
This functionality is currently supported only by DWARF 2 debugging format and the compiler has to produce ‘DW_TAG_call_site’ tags. With GCC, you need to specify -O -g during compilation, to get this information.
The value parameter can be one of the following:
noPrint only actual parameter values, never print values from function entry point.
#0 equal (val=5) #0 different (val=6) #0 lost (val=<optimized out>) #0 born (val=10) #0 invalid (val=<optimized out>)
onlyPrint only parameter values from function entry point. The actual parameter values are never printed.
#0 equal (val@entry=5) #0 different (val@entry=5) #0 lost (val@entry=5) #0 born (val@entry=<optimized out>) #0 invalid (val@entry=<optimized out>)
preferredPrint only parameter values from function entry point. If value from function entry point is not known while the actual value is known, print the actual value for such parameter.
#0 equal (val@entry=5) #0 different (val@entry=5) #0 lost (val@entry=5) #0 born (val=10) #0 invalid (val@entry=<optimized out>)
if-neededPrint actual parameter values. If actual parameter value is not known while value from function entry point is known, print the entry point value for such parameter.
#0 equal (val=5) #0 different (val=6) #0 lost (val@entry=5) #0 born (val=10) #0 invalid (val=<optimized out>)
bothAlways print both the actual parameter value and its value from function entry point, even if values of one or both are not available due to compiler optimizations.
#0 equal (val=5, val@entry=5) #0 different (val=6, val@entry=5) #0 lost (val=<optimized out>, val@entry=5) #0 born (val=10, val@entry=<optimized out>) #0 invalid (val=<optimized out>, val@entry=<optimized out>)
compactPrint the actual parameter value if it is known and also its value from
function entry point if it is known. If neither is known, print for the actual
value <optimized out>. If not in MI mode (see GDB/MI) and if both
values are known and identical, print the shortened
param=param@entry=VALUE notation.
#0 equal (val=val@entry=5) #0 different (val=6, val@entry=5) #0 lost (val@entry=5) #0 born (val=10) #0 invalid (val=<optimized out>)
defaultAlways print the actual parameter value. Print also its value from function
entry point, but only if it is known. If not in MI mode (see GDB/MI) and
if both values are known and identical, print the shortened
param=param@entry=VALUE notation.
#0 equal (val=val@entry=5) #0 different (val=6, val@entry=5) #0 lost (val=<optimized out>, val@entry=5) #0 born (val=10) #0 invalid (val=<optimized out>)
For analysis messages on possible failures of frame argument values at function entry resolution see set debug entry-values.
show print entry-valuesShow the method being used for printing of frame argument values at function entry.
set print repeats number-of-repeatsset print repeats unlimitedSet the threshold for suppressing display of repeated array
elements. When the number of consecutive identical elements of an
array exceeds the threshold, GDB prints the string
"<repeats n times>", where n is the number of
identical repetitions, instead of displaying the identical elements
themselves. Setting the threshold to unlimited or zero will
cause all elements to be individually printed. The default threshold
is 10.
show print repeatsDisplay the current threshold for printing repeated identical elements.
set print null-stopCause 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.
show print null-stopShow whether GDB stops printing an array on the first NULL character.
set print pretty onCause GDB to print structures in an indented format with one member per line, like this:
$1 = {
next = 0x0,
flags = {
sweet = 1,
sour = 1
},
meat = 0x54 "Pork"
}
set print pretty offCause GDB to print structures in a compact format, like this:
$1 = {next = 0x0, flags = {sweet = 1, sour = 1}, \
meat = 0x54 "Pork"}
This is the default format.
show print prettyShow which format GDB is using to print structures.
set print sevenbit-strings onPrint 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 offPrint full eight-bit characters. This allows the use of more international character sets, and is the default.
show print sevenbit-stringsShow whether or not GDB is printing only seven-bit characters.
set print union onTell GDB to print unions which are contained in structures and other unions. This is the default setting.
set print union offTell GDB not to print unions which are contained in
structures and other unions. GDB will print "{...}"
instead.
show print unionAsk GDB whether or not it will print unions which are contained in structures and other unions.
For example, given the declarations
typedef enum {Tree, Bug} Species;
typedef enum {Big_tree, Acorn, Seedling} Tree_forms;
typedef enum {Caterpillar, Cocoon, Butterfly}
Bug_forms;
struct thing {
Species it;
union {
Tree_forms tree;
Bug_forms bug;
} form;
};
struct thing foo = {Tree, {Acorn}};
with set print union on in effect ‘p foo’ would print
$1 = {it = Tree, form = {tree = Acorn, bug = Cocoon}}
and with set print union off in effect it would print
$1 = {it = Tree, form = {...}}
set print union affects programs written in C-like languages
and in Pascal.
These settings are of interest when debugging C++ programs:
set print demangleset print demangle onPrint 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 demangleShow whether C++ names are printed in mangled or demangled form.
set print asm-demangleset print asm-demangle onPrint 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-demangleShow whether C++ names in assembly listings are printed in mangled or demangled form.
set demangle-style styleChoose among several encoding schemes used by different compilers to represent C++ names. If you omit style, you will see a list of possible formats. The default value is auto, which lets GDB choose a decoding style by inspecting your program.
show demangle-styleDisplay the encoding style currently in use for decoding C++ symbols.
set print objectset print object onWhen displaying a pointer to an object, identify the actual (derived) type of the object rather than the declared type, using the virtual function table. Note that the virtual function table is required—this feature can only work for objects that have run-time type identification; a single virtual method in the object’s declared type is sufficient. Note that this setting is also taken into account when working with variable objects via MI (see GDB/MI).
set print object offDisplay only the declared type of objects, without reference to the virtual function table. This is the default setting.
show print objectShow whether actual, or declared, object types are displayed.
set print static-membersset print static-members onPrint static members when displaying a C++ object. The default is on.
set print static-members offDo not print static members when displaying a C++ object.
show print static-membersShow whether C++ static members are printed or not.
set print pascal_static-membersset print pascal_static-members onPrint static members when displaying a Pascal object. The default is on.
set print pascal_static-members offDo not print static members when displaying a Pascal object.
show print pascal_static-membersShow whether Pascal static members are printed or not.
set print vtblset print vtbl onPretty 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 offDo not pretty print C++ virtual function tables.
show print vtblShow whether C++ virtual function tables are pretty printed, or not.
Next: Pretty Printing, Previous: Auto Display, Up: Data [Contents][Index]