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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> |
| <h3 class="section">10.1 Expressions</h3> |
| |
| <a name="index-expressions"></a> |
| <p><code>print</code> and many other <small>GDB</small> 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 |
| <small>GDB</small>. 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 |
| <a href="Compilation.html#Compilation">Compilation</a>. |
| </p> |
| <a name="index-arrays-in-expressions"></a> |
| <p><small>GDB</small> supports array constants in expressions input by |
| the user. The syntax is {<var>element</var>, <var>element</var>…}. For example, |
| you can use the command <code>print {1, 2, 3}</code> to create an array |
| of three integers. If you pass an array to a function or assign it |
| to a program variable, <small>GDB</small> copies the array to memory that |
| is <code>malloc</code>ed in the target program. |
| </p> |
| <p>Because C is so widespread, most of the expressions shown in examples in |
| this manual are in C. See <a href="Languages.html#Languages">Using <small>GDB</small> with Different |
| Languages</a>, for information on how to use expressions in other |
| languages. |
| </p> |
| <p>In this section, we discuss operators that you can use in <small>GDB</small> |
| expressions regardless of your programming language. |
| </p> |
| <a name="index-casts_002c-in-expressions"></a> |
| <p>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. |
| </p> |
| <p><small>GDB</small> supports these operators, in addition to those common |
| to programming languages: |
| </p> |
| <dl compact="compact"> |
| <dt><code>@</code></dt> |
| <dd><p>‘<samp>@</samp>’ is a binary operator for treating parts of memory as arrays. |
| See <a href="Arrays.html#Arrays">Artificial Arrays</a>, for more information. |
| </p> |
| </dd> |
| <dt><code>::</code></dt> |
| <dd><p>‘<samp>::</samp>’ allows you to specify a variable in terms of the file or |
| function where it is defined. See <a href="Variables.html#Variables">Program Variables</a>. |
| </p> |
| <a name="index-_007btype_007d"></a> |
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| <a name="index-memory_002c-viewing-as-typed-object"></a> |
| <a name="index-casts_002c-to-view-memory"></a> |
| </dd> |
| <dt><code>{<var>type</var>} <var>addr</var></code></dt> |
| <dd><p>Refers to an object of type <var>type</var> stored at address <var>addr</var> in |
| memory. The address <var>addr</var> 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 <var>addr</var>. |
| </p></dd> |
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