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| <h5 class="subsubsection">15.4.1.1 C and C<tt>++</tt> Operators</h5> |
| |
| <p><a name="index-C-and-C_0040t_007b_002b_002b_007d-operators-798"></a> |
| 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>For the purposes of C and C<tt>++</tt>, the following definitions hold: |
| |
| <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><em>Floating-point types</em> include <code>float</code>, <code>double</code>, and |
| <code>long double</code> (if supported by the target platform). |
| |
| <li><em>Pointer types</em> include all types defined as <code>(</code><var>type</var><code> *)</code>. |
| |
| <li><em>Scalar types</em> include all of the above. |
| |
| </ul> |
| |
| <p class="noindent">The following operators are supported. They are listed here |
| in order of increasing precedence: |
| |
| <dl> |
| <dt><code>,</code><dd>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. |
| |
| <br><dt><code>=</code><dd>Assignment. The value of an assignment expression is the value |
| assigned. Defined on scalar types. |
| |
| <br><dt><var>op</var><code>=</code><dd>Used in an expression of the form <var>a</var><code> </code><var>op</var><code>= </code><var>b</var><!-- /@w -->, |
| and translated to <var>a</var><code> = </code><var>a op b</var><!-- /@w -->. |
| <var>op</var><code>=</code><!-- /@w --> and <code>=</code> have the same precedence. |
| <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>. |
| |
| <br><dt><code>?:</code><dd>The ternary operator. <var>a</var><code> ? </code><var>b</var><code> : </code><var>c</var> can be thought |
| of as: if <var>a</var> then <var>b</var> else <var>c</var>. <var>a</var> should be of an |
| integral type. |
| |
| <br><dt><code>||</code><dd>Logical <span class="sc">or</span>. Defined on integral types. |
| |
| <br><dt><code>&&</code><dd>Logical <span class="sc">and</span>. Defined on integral types. |
| |
| <br><dt><code>|</code><dd>Bitwise <span class="sc">or</span>. Defined on integral types. |
| |
| <br><dt><code>^</code><dd>Bitwise exclusive-<span class="sc">or</span>. Defined on integral types. |
| |
| <br><dt><code>&</code><dd>Bitwise <span class="sc">and</span>. Defined on integral types. |
| |
| <br><dt><code>==</code><span class="roman">, </span><code>!=</code><dd>Equality and inequality. Defined on scalar types. The value of these |
| expressions is 0 for false and non-zero for true. |
| |
| <br><dt><code><</code><span class="roman">, </span><code>></code><span class="roman">, </span><code><=</code><span class="roman">, </span><code>>=</code><dd>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. |
| |
| <br><dt><code><<</code><span class="roman">, </span><code>>></code><dd>left shift, and right shift. Defined on integral types. |
| |
| <br><dt><code>@</code><dd>The <span class="sc">gdb</span> “artificial array” operator (see <a href="Expressions.html#Expressions">Expressions</a>). |
| |
| <br><dt><code>+</code><span class="roman">, </span><code>-</code><dd>Addition and subtraction. Defined on integral types, floating-point types and |
| pointer types. |
| |
| <br><dt><code>*</code><span class="roman">, </span><code>/</code><span class="roman">, </span><code>%</code><dd>Multiplication, division, and modulus. Multiplication and division are |
| defined on integral and floating-point types. Modulus is defined on |
| integral types. |
| |
| <br><dt><code>++</code><span class="roman">, </span><code>--</code><dd>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. |
| |
| <br><dt><code>*</code><dd>Pointer dereferencing. Defined on pointer types. Same precedence as |
| <code>++</code>. |
| |
| <br><dt><code>&</code><dd>Address operator. Defined on variables. Same precedence as <code>++</code>. |
| |
| <p>For debugging C<tt>++</tt>, <span class="sc">gdb</span> implements a use of ‘<samp><span class="samp">&</span></samp>’ beyond what is |
| allowed in the C<tt>++</tt> language itself: you can use ‘<samp><span class="samp">&(&</span><var>ref</var><span class="samp">)</span></samp>’ |
| to examine the address |
| where a C<tt>++</tt> reference variable (declared with ‘<samp><span class="samp">&</span><var>ref</var></samp>’) is |
| stored. |
| |
| <br><dt><code>-</code><dd>Negative. Defined on integral and floating-point types. Same |
| precedence as <code>++</code>. |
| |
| <br><dt><code>!</code><dd>Logical negation. Defined on integral types. Same precedence as |
| <code>++</code>. |
| |
| <br><dt><code>~</code><dd>Bitwise complement operator. Defined on integral types. Same precedence as |
| <code>++</code>. |
| |
| <br><dt><code>.</code><span class="roman">, </span><code>-></code><dd>Structure member, and pointer-to-structure member. For convenience, |
| <span class="sc">gdb</span> 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. |
| |
| <br><dt><code>.*</code><span class="roman">, </span><code>->*</code><dd>Dereferences of pointers to members. |
| |
| <br><dt><code>[]</code><dd>Array indexing. <var>a</var><code>[</code><var>i</var><code>]</code> is defined as |
| <code>*(</code><var>a</var><code>+</code><var>i</var><code>)</code>. Same precedence as <code>-></code>. |
| |
| <br><dt><code>()</code><dd>Function parameter list. Same precedence as <code>-></code>. |
| |
| <br><dt><code>::</code><dd>C<tt>++</tt> scope resolution operator. Defined on <code>struct</code>, <code>union</code>, |
| and <code>class</code> types. |
| |
| <br><dt><code>::</code><dd>Doubled colons also represent the <span class="sc">gdb</span> scope operator |
| (see <a href="Expressions.html#Expressions">Expressions</a>). Same precedence as <code>::</code>, |
| above. |
| </dl> |
| |
| <p>If an operator is redefined in the user code, <span class="sc">gdb</span> usually |
| attempts to invoke the redefined version instead of using the operator's |
| predefined meaning. |
| |
| </body></html> |
| |
