10.5 Output Formats
By default, gdb prints a value according to its data type. Sometimes
this is not what you want. For example, you might want to print a number
in hex, or a pointer in decimal. Or you might want to view data in memory
at a certain address as a character string or as an instruction. To do
these things, specify an output format when you print a value.
The simplest use of output formats is to say how to print a value
already computed. This is done by starting the arguments of the
print command with a slash and a format letter. The format
letters supported are:
- Regard the bits of the value as an integer, and print the integer in
- Print as integer in signed decimal.
- Print as integer in unsigned decimal.
- Print as integer in octal.
- Print as integer in binary. The letter ‘t’ stands for “two”.
- Print as an address, both absolute in hexadecimal and as an offset from
the nearest preceding symbol. You can use this format used to discover
where (in what function) an unknown address is located:
(gdb) p/a 0x54320
$3 = 0x54320 <_initialize_vx+396>
info symbol 0x54320 yields similar results.
See info symbol.
- Regard as an integer and print it as a character constant. This
prints both the numerical value and its character representation. The
character representation is replaced with the octal escape ‘\nnn’
for characters outside the 7-bit ascii range.
Without this format, gdb displays
unsigned char, and
signed char data as character
constants. Single-byte members of vectors are displayed as integer
- Regard the bits of the value as a floating point number and print
using typical floating point syntax.
- Regard as a string, if possible. With this format, pointers to single-byte
data are displayed as null-terminated strings and arrays of single-byte data
are displayed as fixed-length strings. Other values are displayed in their
Without this format, gdb displays pointers to and arrays of
unsigned char, and
signed char as
strings. Single-byte members of a vector are displayed as an integer
- Like ‘x’ formatting, the value is treated as an integer and
printed as hexadecimal, but leading zeros are printed to pad the value
to the size of the integer type.
- Print using the ‘raw’ formatting. By default, gdb will
use a Python-based pretty-printer, if one is available (see Pretty Printing). This typically results in a higher-level display of the
value's contents. The ‘r’ format bypasses any Python
pretty-printer which might exist.
For example, to print the program counter in hex (see Registers), type
Note that no space is required before the slash; this is because command
names in gdb cannot contain a slash.
To reprint the last value in the value history with a different format,
you can use the
print command with just a format and no
expression. For example, ‘p/x’ reprints the last value in hex.