If you find that you want to print the value of an expression frequently (to see how it changes), you might want to add it to the automatic display list so that GDB prints its value each time your program stops. Each expression added to the list is given a number to identify it; to remove an expression from the list, you specify that number. The automatic display looks like this:
2: foo = 38 3: bar = (struct hack *) 0x3804
This display shows item numbers, expressions and their current values. As with
displays you request manually using
whether to use
x depending on how elaborate your
format specification is--it uses
x if you specify a unit size,
or one of the two formats (`i' and `s') that are only
x; otherwise it uses
displaydoes not repeat if you press RET again after using it.
For example, `display/i $pc' can be helpful, to see the machine instruction about to be executed each time execution stops (`$pc' is a common name for the program counter; see section Registers).
delete display dnums...
undisplaydoes not repeat if you press RET after using it. (Otherwise you would just get the error `No display number ...'.)
disable display dnums...
enable display dnums...
If a display expression refers to local variables, then it does not make
sense outside the lexical context for which it was set up. Such an
expression is disabled when execution enters a context where one of its
variables is not defined. For example, if you give the command
display last_char while inside a function with an argument
last_char, GDB displays this argument while your program
continues to stop inside that function. When it stops elsewhere--where
there is no variable
last_char---the display is disabled
automatically. The next time your program stops where
is meaningful, you can enable the display expression once again.
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