gdb: Expressions
10.1 Expressions
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'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.
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 create an array of three integers. If you pass an
array to a function or assign it to a program variable, GDB copies the
array to 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. Using GDB with Different Languages
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.
Artificial Arrays Arrays, for more information.
'::'
'::' allows you to specify a variable in terms of the file or
function where it is defined. Program Variables Variables.
'{TYPE} ADDR'
Refers to an object of type TYPE stored at address ADDR in memory.
The address ADDR may be any expression whose value is an integer or
pointer (but parentheses are required around binary operators, just
as in a cast). This construct is allowed regardless of what kind
of data is normally supposed to reside at ADDR.
Info Catalog
gdb: Data
gdb: Ambiguous Expressions