print
and many other GDB commands accept an expression and
compute its value. Any kind of constant, variable or operator defined
by the programming language you are using is valid in an expression in
GDB. This includes conditional expressions, function calls,
casts, and string constants. It also includes preprocessor macros, if
you compiled your program to include this information; see
Compilation.
Beware that nested functions usually need a context to be setup before
being called. Unfortunately, GDB currently has no knowledge of this
setup, and hence can not perform the calls to nested functions in a
fully appropriate manner. As a consequence, the result of such a call is
likely to be erroneous, and even cause a crash of the program being
debugged.
GDB supports array constants in expressions input by
the user. The syntax is {element, element...}. For example,
you can use the command print {1, 2, 3}
to build up an array in
memory that is malloc
ed in the target program.
Because C is so widespread, most of the expressions shown in examples in this manual are in C. See Using GDB with Different Languages, for information on how to use expressions in other languages.
In this section, we discuss operators that you can use in GDB expressions regardless of your programming language.
Casts are supported in all languages, not just in C, because it is so useful to cast a number into a pointer in order to examine a structure at that address in memory. GDB supports these operators, in addition to those common to programming languages:
@
@
is a binary operator for treating parts of memory as arrays.
See Artificial arrays, for more information.
::
::
allows you to specify a variable in terms of the file or
function where it is defined. See Program variables.
{
type}
addr