Expressions

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Expressions

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 unfortunately does not include symbols defined by preprocessor #define commands.

GDB supports array constants in expressions input by the user.

The syntax uses the following example's declaration.

element, element ...

For example, you can now use the command, print {1 2 3} to build up an array in memory that is memory allocated in the target program.

Note:
Because C is so widespread, most of the expressions shown in examples in this documentation are in C. See Using GDB with Different Languages for information on how to use expressions in other languages. In this documentation, 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 the following 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

Refers to an object of type, type, stored at address, addr, in memory. 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.

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