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<title>Debugging with GDB: Expressions</title>
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<a name="Expressions"></a>
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<p>
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Next: <a href="Ambiguous-Expressions.html#Ambiguous-Expressions" accesskey="n" rel="next">Ambiguous Expressions</a>, Up: <a href="Data.html#Data" accesskey="u" rel="up">Data</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Expressions-1"></a>
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<h3 class="section">10.1 Expressions</h3>
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<a name="index-expressions"></a>
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<p><code>print</code> and many other <small>GDB</small> commands accept an expression and
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compute its value. Any kind of constant, variable or operator defined
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by the programming language you are using is valid in an expression in
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<small>GDB</small>. This includes conditional expressions, function calls,
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casts, and string constants. It also includes preprocessor macros, if
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you compiled your program to include this information; see
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<a href="Compilation.html#Compilation">Compilation</a>.
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</p>
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<a name="index-arrays-in-expressions"></a>
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<p><small>GDB</small> supports array constants in expressions input by
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the user. The syntax is {<var>element</var>, <var>element</var>…}. For example,
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you can use the command <code>print {1, 2, 3}</code> to create an array
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of three integers. If you pass an array to a function or assign it
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to a program variable, <small>GDB</small> copies the array to memory that
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is <code>malloc</code>ed in the target program.
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</p>
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<p>Because C is so widespread, most of the expressions shown in examples in
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this manual are in C. See <a href="Languages.html#Languages">Using <small>GDB</small> with Different
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Languages</a>, for information on how to use expressions in other
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languages.
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</p>
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<p>In this section, we discuss operators that you can use in <small>GDB</small>
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expressions regardless of your programming language.
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</p>
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<a name="index-casts_002c-in-expressions"></a>
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<p>Casts are supported in all languages, not just in C, because it is so
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useful to cast a number into a pointer in order to examine a structure
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at that address in memory.
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</p>
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<p><small>GDB</small> supports these operators, in addition to those common
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to programming languages:
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</p>
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<dl compact="compact">
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<dt><code>@</code></dt>
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<dd><p>‘<samp>@</samp>’ is a binary operator for treating parts of memory as arrays.
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See <a href="Arrays.html#Arrays">Artificial Arrays</a>, for more information.
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</p>
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</dd>
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<dt><code>::</code></dt>
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<dd><p>‘<samp>::</samp>’ allows you to specify a variable in terms of the file or
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function where it is defined. See <a href="Variables.html#Variables">Program Variables</a>.
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</p>
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<a name="index-_007btype_007d"></a>
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<a name="index-type-casting-memory"></a>
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<a name="index-memory_002c-viewing-as-typed-object"></a>
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<a name="index-casts_002c-to-view-memory"></a>
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</dd>
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<dt><code>{<var>type</var>} <var>addr</var></code></dt>
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<dd><p>Refers to an object of type <var>type</var> stored at address <var>addr</var> in
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memory. The address <var>addr</var> may be any expression whose value is
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an integer or pointer (but parentheses are required around binary
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operators, just as in a cast). This construct is allowed regardless
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of what kind of data is normally supposed to reside at <var>addr</var>.
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</p></dd>
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Next: <a href="Ambiguous-Expressions.html#Ambiguous-Expressions" accesskey="n" rel="next">Ambiguous Expressions</a>, Up: <a href="Data.html#Data" accesskey="u" rel="up">Data</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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