You can use the command
x (for "examine") to examine memory in
any of several formats, independently of your program's data types.
xcommand to examine memory.
n, f, and u are all optional parameters that specify how much memory to display and how to format it; addr is an expression giving the address where you want to start displaying memory. If you use defaults for nfu, you need not type the slash `/'. Several commands set convenient defaults for addr.
x, that size becomes the default unit the next time you use
x. (For the `s' and `i' formats, the unit size is ignored and is normally not written.)
info breakpoints(to the address of the last breakpoint listed),
info line(to the starting address of a line), and
For example, `x/3uh 0x54320' is a request to display three halfwords
h) of memory, formatted as unsigned decimal integers (`u'),
starting at address
0x54320. `x/4xw $sp' prints the four
words (`w') of memory above the stack pointer (here, `$sp';
see section Registers) in hexadecimal (`x').
Since the letters indicating unit sizes are all distinct from the letters specifying output formats, you do not have to remember whether unit size or format comes first; either order works. The output specifications `4xw' and `4wx' mean exactly the same thing. (However, the count n must come first; `wx4' does not work.)
Even though the unit size u is ignored for the formats `s'
and `i', you might still want to use a count n; for example,
`3i' specifies that you want to see three machine instructions,
including any operands. The command
disassemble gives an
alternative way of inspecting machine instructions; see section Source and machine code.
All the defaults for the arguments to
x are designed to make it
easy to continue scanning memory with minimal specifications each time
x. For example, after you have inspected three machine
instructions with `x/3i addr', you can inspect the next seven
with just `x/7'. If you use RET to repeat the
the repeat count n is used again; the other arguments default as
for successive uses of
The addresses and contents printed by the
x command are not saved
in the value history because there is often too much of them and they
would get in the way. Instead, GDB makes these values available for
subsequent use in expressions as values of the convenience variables
$__. After an
x command, the last address
examined is available for use in expressions in the convenience variable
$_. The contents of that address, as examined, are available in
the convenience variable
x command has a repeat count, the address and contents saved
are from the last memory unit printed; this is not the same as the last
address printed if several units were printed on the last line of output.
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