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| <a name="C-Operators"></a> |
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| Next: <a href="C-Constants.html#C-Constants" accesskey="n" rel="next">C Constants</a>, Up: <a href="C.html#C" accesskey="u" rel="up">C</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="C-and-C_002b_002b-Operators"></a> |
| <h4 class="subsubsection">15.4.1.1 C and C<tt>++</tt> Operators</h4> |
| |
| <a name="index-C-and-C_002b_002b-operators"></a> |
| |
| <p>Operators must be defined on values of specific types. For instance, |
| <code>+</code> is defined on numbers, but not on structures. Operators are |
| often defined on groups of types. |
| </p> |
| <p>For the purposes of C and C<tt>++</tt>, the following definitions hold: |
| </p> |
| <ul> |
| <li> <em>Integral types</em> include <code>int</code> with any of its storage-class |
| specifiers; <code>char</code>; <code>enum</code>; and, for C<tt>++</tt>, <code>bool</code>. |
| |
| </li><li> <em>Floating-point types</em> include <code>float</code>, <code>double</code>, and |
| <code>long double</code> (if supported by the target platform). |
| |
| </li><li> <em>Pointer types</em> include all types defined as <code>(<var>type</var> *)</code>. |
| |
| </li><li> <em>Scalar types</em> include all of the above. |
| |
| </li></ul> |
| |
| <p>The following operators are supported. They are listed here |
| in order of increasing precedence: |
| </p> |
| <dl compact="compact"> |
| <dt><code>,</code></dt> |
| <dd><p>The comma or sequencing operator. Expressions in a comma-separated list |
| are evaluated from left to right, with the result of the entire |
| expression being the last expression evaluated. |
| </p> |
| </dd> |
| <dt><code>=</code></dt> |
| <dd><p>Assignment. The value of an assignment expression is the value |
| assigned. Defined on scalar types. |
| </p> |
| </dd> |
| <dt><code><var>op</var>=</code></dt> |
| <dd><p>Used in an expression of the form <code><var>a</var> <var>op</var>= <var>b</var></code><!-- /@w -->, |
| and translated to <code><var>a</var> = <var>a op b</var></code><!-- /@w -->. |
| <code><var>op</var>=</code><!-- /@w --> and <code>=</code> have the same precedence. The operator |
| <var>op</var> is any one of the operators <code>|</code>, <code>^</code>, <code>&</code>, |
| <code><<</code>, <code>>></code>, <code>+</code>, <code>-</code>, <code>*</code>, <code>/</code>, <code>%</code>. |
| </p> |
| </dd> |
| <dt><code>?:</code></dt> |
| <dd><p>The ternary operator. <code><var>a</var> ? <var>b</var> : <var>c</var></code> can be thought |
| of as: if <var>a</var> then <var>b</var> else <var>c</var>. The argument <var>a</var> |
| should be of an integral type. |
| </p> |
| </dd> |
| <dt><code>||</code></dt> |
| <dd><p>Logical <small>OR</small>. Defined on integral types. |
| </p> |
| </dd> |
| <dt><code>&&</code></dt> |
| <dd><p>Logical <small>AND</small>. Defined on integral types. |
| </p> |
| </dd> |
| <dt><code>|</code></dt> |
| <dd><p>Bitwise <small>OR</small>. Defined on integral types. |
| </p> |
| </dd> |
| <dt><code>^</code></dt> |
| <dd><p>Bitwise exclusive-<small>OR</small>. Defined on integral types. |
| </p> |
| </dd> |
| <dt><code>&</code></dt> |
| <dd><p>Bitwise <small>AND</small>. Defined on integral types. |
| </p> |
| </dd> |
| <dt><code>==<span class="roman">, </span>!=</code></dt> |
| <dd><p>Equality and inequality. Defined on scalar types. The value of these |
| expressions is 0 for false and non-zero for true. |
| </p> |
| </dd> |
| <dt><code><<span class="roman">, </span>><span class="roman">, </span><=<span class="roman">, </span>>=</code></dt> |
| <dd><p>Less than, greater than, less than or equal, greater than or equal. |
| Defined on scalar types. The value of these expressions is 0 for false |
| and non-zero for true. |
| </p> |
| </dd> |
| <dt><code><<<span class="roman">, </span>>></code></dt> |
| <dd><p>left shift, and right shift. Defined on integral types. |
| </p> |
| </dd> |
| <dt><code>@</code></dt> |
| <dd><p>The <small>GDB</small> “artificial array” operator (see <a href="Expressions.html#Expressions">Expressions</a>). |
| </p> |
| </dd> |
| <dt><code>+<span class="roman">, </span>-</code></dt> |
| <dd><p>Addition and subtraction. Defined on integral types, floating-point types and |
| pointer types. |
| </p> |
| </dd> |
| <dt><code>*<span class="roman">, </span>/<span class="roman">, </span>%</code></dt> |
| <dd><p>Multiplication, division, and modulus. Multiplication and division are |
| defined on integral and floating-point types. Modulus is defined on |
| integral types. |
| </p> |
| </dd> |
| <dt><code>++<span class="roman">, </span>--</code></dt> |
| <dd><p>Increment and decrement. When appearing before a variable, the |
| operation is performed before the variable is used in an expression; |
| when appearing after it, the variable’s value is used before the |
| operation takes place. |
| </p> |
| </dd> |
| <dt><code>*</code></dt> |
| <dd><p>Pointer dereferencing. Defined on pointer types. Same precedence as |
| <code>++</code>. |
| </p> |
| </dd> |
| <dt><code>&</code></dt> |
| <dd><p>Address operator. Defined on variables. Same precedence as <code>++</code>. |
| </p> |
| <p>For debugging C<tt>++</tt>, <small>GDB</small> implements a use of ‘<samp>&</samp>’ beyond what is |
| allowed in the C<tt>++</tt> language itself: you can use ‘<samp>&(&<var>ref</var>)</samp>’ |
| to examine the address |
| where a C<tt>++</tt> reference variable (declared with ‘<samp>&<var>ref</var></samp>’) is |
| stored. |
| </p> |
| </dd> |
| <dt><code>-</code></dt> |
| <dd><p>Negative. Defined on integral and floating-point types. Same |
| precedence as <code>++</code>. |
| </p> |
| </dd> |
| <dt><code>!</code></dt> |
| <dd><p>Logical negation. Defined on integral types. Same precedence as |
| <code>++</code>. |
| </p> |
| </dd> |
| <dt><code>~</code></dt> |
| <dd><p>Bitwise complement operator. Defined on integral types. Same precedence as |
| <code>++</code>. |
| </p> |
| |
| </dd> |
| <dt><code>.<span class="roman">, </span>-></code></dt> |
| <dd><p>Structure member, and pointer-to-structure member. For convenience, |
| <small>GDB</small> regards the two as equivalent, choosing whether to dereference a |
| pointer based on the stored type information. |
| Defined on <code>struct</code> and <code>union</code> data. |
| </p> |
| </dd> |
| <dt><code>.*<span class="roman">, </span>->*</code></dt> |
| <dd><p>Dereferences of pointers to members. |
| </p> |
| </dd> |
| <dt><code>[]</code></dt> |
| <dd><p>Array indexing. <code><var>a</var>[<var>i</var>]</code> is defined as |
| <code>*(<var>a</var>+<var>i</var>)</code>. Same precedence as <code>-></code>. |
| </p> |
| </dd> |
| <dt><code>()</code></dt> |
| <dd><p>Function parameter list. Same precedence as <code>-></code>. |
| </p> |
| </dd> |
| <dt><code>::</code></dt> |
| <dd><p>C<tt>++</tt> scope resolution operator. Defined on <code>struct</code>, <code>union</code>, |
| and <code>class</code> types. |
| </p> |
| </dd> |
| <dt><code>::</code></dt> |
| <dd><p>Doubled colons also represent the <small>GDB</small> scope operator |
| (see <a href="Expressions.html#Expressions">Expressions</a>). Same precedence as <code>::</code>, |
| above. |
| </p></dd> |
| </dl> |
| |
| <p>If an operator is redefined in the user code, <small>GDB</small> usually |
| attempts to invoke the redefined version instead of using the operator’s |
| predefined meaning. |
| </p> |
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