mingw/info/gdb/C-Operators.html

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  12 Node:<a name="C%20Operators">C Operators</a>,
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  17
  18 <h5 class="subsubsection">C and C<tt>++</tt> operators</h5>
  19
  20    <p>Operators must be defined on values of specific types.  For instance,
  21 <code>+</code> is defined on numbers, but not on structures.  Operators are
  22 often defined on groups of types.
  23
  24    <p>For the purposes of C and C<tt>++</tt>, the following definitions hold:
  25
  26      <ul>
  27
  28      <li><em>Integral types</em> include <code>int</code> with any of its storage-class
  29 specifiers; <code>char</code>; <code>enum</code>; and, for C<tt>++</tt>, <code>bool</code>.
  30
  31      <li><em>Floating-point types</em> include <code>float</code>, <code>double</code>, and
  32 <code>long double</code> (if supported by the target platform).
  33
  34      <li><em>Pointer types</em> include all types defined as <code>(</code><var>type</var><code> *)</code>.
  35
  36      <li><em>Scalar types</em> include all of the above.
  37
  38    </ul>
  39
  40 <p>The following operators are supported.  They are listed here
  41 in order of increasing precedence:
  42
  43      <dl>
  44 <dt><code>,</code>
  45      <dd>The comma or sequencing operator.  Expressions in a comma-separated list
  46 are evaluated from left to right, with the result of the entire
  47 expression being the last expression evaluated.
  48
  49      <br><dt><code>=</code>
  50      <dd>Assignment.  The value of an assignment expression is the value
  51 assigned.  Defined on scalar types.
  52
  53      <br><dt><code></code><var>op</var><code>=</code>
  54      <dd>Used in an expression of the form <code></code><var>a</var><code>&nbsp;</code><var>op</var><code>=&nbsp;</code><var>b</var><code></code>,
  55 and translated to <code></code><var>a</var><code>&nbsp;=&nbsp;</code><var>a&nbsp;op&nbsp;b</var><code></code>.
  56 <code></code><var>op</var><code>=</code> and <code>=</code> have the same precedence.
  57 <var>op</var> is any one of the operators <code>|</code>, <code>^</code>, <code>&amp;</code>,
  58 <code>&lt;&lt;</code>, <code>&gt;&gt;</code>, <code>+</code>, <code>-</code>, <code>*</code>, <code>/</code>, <code>%</code>.
  59
  60      <br><dt><code>?:</code>
  61      <dd>The ternary operator.  <code></code><var>a</var><code> ? </code><var>b</var><code> : </code><var>c</var><code></code> can be thought
  62 of as:  if <var>a</var> then <var>b</var> else <var>c</var>.  <var>a</var> should be of an
  63 integral type.
  64
  65      <br><dt><code>||</code>
  66      <dd>Logical <small>OR</small>.  Defined on integral types.
  67
  68      <br><dt><code>&amp;&amp;</code>
  69      <dd>Logical <small>AND</small>.  Defined on integral types.
  70
  71      <br><dt><code>|</code>
  72      <dd>Bitwise <small>OR</small>.  Defined on integral types.
  73
  74      <br><dt><code>^</code>
  75      <dd>Bitwise exclusive-<small>OR</small>.  Defined on integral types.
  76
  77      <br><dt><code>&amp;</code>
  78      <dd>Bitwise <small>AND</small>.  Defined on integral types.
  79
  80      <br><dt><code>==</code>, <code>!=</code>
  81      <dd>Equality and inequality.  Defined on scalar types.  The value of these
  82 expressions is 0 for false and non-zero for true.
  83
  84      <br><dt><code>&lt;</code>, <code>&gt;</code>, <code>&lt;=</code>, <code>&gt;=</code>
  85      <dd>Less than, greater than, less than or equal, greater than or equal.
  86 Defined on scalar types.  The value of these expressions is 0 for false
  87 and non-zero for true.
  88
  89      <br><dt><code>&lt;&lt;</code>, <code>&gt;&gt;</code>
  90      <dd>left shift, and right shift.  Defined on integral types.
  91
  92      <br><dt><code>@</code>
  93      <dd>The GDB "artificial array" operator (see <a href="Expressions.html#Expressions">Expressions</a>).
  94
  95      <br><dt><code>+</code>, <code>-</code>
  96      <dd>Addition and subtraction.  Defined on integral types, floating-point types and
  97 pointer types.
  98
  99      <br><dt><code>*</code>, <code>/</code>, <code>%</code>
 100      <dd>Multiplication, division, and modulus.  Multiplication and division are
 101 defined on integral and floating-point types.  Modulus is defined on
 102 integral types.
 103
 104      <br><dt><code>++</code>, <code>--</code>
 105      <dd>Increment and decrement.  When appearing before a variable, the
 106 operation is performed before the variable is used in an expression;
 107 when appearing after it, the variable's value is used before the
 108 operation takes place.
 109
 110      <br><dt><code>*</code>
 111      <dd>Pointer dereferencing.  Defined on pointer types.  Same precedence as
 112 <code>++</code>.
 113
 114      <br><dt><code>&amp;</code>
 115      <dd>Address operator.  Defined on variables.  Same precedence as <code>++</code>.
 116
 117      <p>For debugging C<tt>++</tt>, GDB implements a use of <code>&amp;</code> beyond what is
 118 allowed in the C<tt>++</tt> language itself: you can use <code>&amp;(&amp;</code><var>ref</var><code>)</code>
 119 (or, if you prefer, simply <code>&amp;&amp;</code><var>ref</var><code></code>) to examine the address
 120 where a C<tt>++</tt> reference variable (declared with <code>&amp;</code><var>ref</var><code></code>) is
 121 stored.
 122
 123      <br><dt><code>-</code>
 124      <dd>Negative.  Defined on integral and floating-point types.  Same
 125 precedence as <code>++</code>.
 126
 127      <br><dt><code>!</code>
 128      <dd>Logical negation.  Defined on integral types.  Same precedence as
 129 <code>++</code>.
 130
 131      <br><dt><code>~</code>
 132      <dd>Bitwise complement operator.  Defined on integral types.  Same precedence as
 133 <code>++</code>.
 134
 135      <br><dt><code>.</code>, <code>-&gt;</code>
 136      <dd>Structure member, and pointer-to-structure member.  For convenience,
 137 GDB regards the two as equivalent, choosing whether to dereference a
 138 pointer based on the stored type information.
 139 Defined on <code>struct</code> and <code>union</code> data.
 140
 141      <br><dt><code>.*</code>, <code>-&gt;*</code>
 142      <dd>Dereferences of pointers to members.
 143
 144      <br><dt><code>[]</code>
 145      <dd>Array indexing.  <code></code><var>a</var><code>[</code><var>i</var><code>]</code> is defined as
 146 <code>*(</code><var>a</var><code>+</code><var>i</var><code>)</code>.  Same precedence as <code>-&gt;</code>.
 147
 148      <br><dt><code>()</code>
 149      <dd>Function parameter list.  Same precedence as <code>-&gt;</code>.
 150
 151      <br><dt><code>::</code>
 152      <dd>C<tt>++</tt> scope resolution operator.  Defined on <code>struct</code>, <code>union</code>,
 153 and <code>class</code> types.
 154
 155      <br><dt><code>::</code>
 156      <dd>Doubled colons also represent the GDB scope operator
 157 (see <a href="Expressions.html#Expressions">Expressions</a>).  Same precedence as <code>::</code>,
 158 above.
 159 </dl>
 160
 161    <p>If an operator is redefined in the user code, GDB usually
 162 attempts to invoke the redefined version instead of using the operator's
 163 predefined meaning.
 164
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