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| <h5 class="subsubsection">15.4.10.3 Additions to Ada</h5> |
| |
| <p><a name="index-Ada_002c-deviations-from-1063"></a> |
| As it does for other languages, <span class="sc">gdb</span> makes certain generic |
| extensions to Ada (see <a href="Expressions.html#Expressions">Expressions</a>): |
| |
| <ul> |
| <li>If the expression <var>E</var> is a variable residing in memory (typically |
| a local variable or array element) and <var>N</var> is a positive integer, |
| then <var>E</var><code>@</code><var>N</var> displays the values of <var>E</var> and the |
| <var>N</var>-1 adjacent variables following it in memory as an array. In |
| Ada, this operator is generally not necessary, since its prime use is |
| in displaying parts of an array, and slicing will usually do this in |
| Ada. However, there are occasional uses when debugging programs in |
| which certain debugging information has been optimized away. |
| |
| <li><var>B</var><code>::</code><var>var</var> means “the variable named <var>var</var> that |
| appears in function or file <var>B</var>.” When <var>B</var> is a file name, |
| you must typically surround it in single quotes. |
| |
| <li>The expression <code>{</code><var>type</var><code>} </code><var>addr</var> means “the variable of type |
| <var>type</var> that appears at address <var>addr</var>.” |
| |
| <li>A name starting with ‘<samp><span class="samp">$</span></samp>’ is a convenience variable |
| (see <a href="Convenience-Vars.html#Convenience-Vars">Convenience Vars</a>) or a machine register (see <a href="Registers.html#Registers">Registers</a>). |
| </ul> |
| |
| <p>In addition, <span class="sc">gdb</span> provides a few other shortcuts and outright |
| additions specific to Ada: |
| |
| <ul> |
| <li>The assignment statement is allowed as an expression, returning |
| its right-hand operand as its value. Thus, you may enter |
| |
| <pre class="smallexample"> (gdb) set x := y + 3 |
| (gdb) print A(tmp := y + 1) |
| </pre> |
| <li>The semicolon is allowed as an “operator,” returning as its value |
| the value of its right-hand operand. |
| This allows, for example, |
| complex conditional breaks: |
| |
| <pre class="smallexample"> (gdb) break f |
| (gdb) condition 1 (report(i); k += 1; A(k) > 100) |
| </pre> |
| <li>Rather than use catenation and symbolic character names to introduce special |
| characters into strings, one may instead use a special bracket notation, |
| which is also used to print strings. A sequence of characters of the form |
| ‘<samp><span class="samp">["</span><var>XX</var><span class="samp">"]</span></samp>’ within a string or character literal denotes the |
| (single) character whose numeric encoding is <var>XX</var> in hexadecimal. The |
| sequence of characters ‘<samp><span class="samp">["""]</span></samp>’ also denotes a single quotation mark |
| in strings. For example, |
| <pre class="smallexample"> "One line.["0a"]Next line.["0a"]" |
| </pre> |
| <p class="noindent">contains an ASCII newline character (<code>Ada.Characters.Latin_1.LF</code>) |
| after each period. |
| |
| <li>The subtype used as a prefix for the attributes <tt>'Pos</tt>, <tt>'Min</tt>, and |
| <tt>'Max</tt> is optional (and is ignored in any case). For example, it is valid |
| to write |
| |
| <pre class="smallexample"> (gdb) print 'max(x, y) |
| </pre> |
| <li>When printing arrays, <span class="sc">gdb</span> uses positional notation when the |
| array has a lower bound of 1, and uses a modified named notation otherwise. |
| For example, a one-dimensional array of three integers with a lower bound |
| of 3 might print as |
| |
| <pre class="smallexample"> (3 => 10, 17, 1) |
| </pre> |
| <p class="noindent">That is, in contrast to valid Ada, only the first component has a <code>=></code> |
| clause. |
| |
| <li>You may abbreviate attributes in expressions with any unique, |
| multi-character subsequence of |
| their names (an exact match gets preference). |
| For example, you may use <tt>a'len</tt>, <tt>a'gth</tt>, or <tt>a'lh</tt> |
| in place of <tt>a'length</tt>. |
| |
| <li><a name="index-quoting-Ada-internal-identifiers-1064"></a>Since Ada is case-insensitive, the debugger normally maps identifiers you type |
| to lower case. The GNAT compiler uses upper-case characters for |
| some of its internal identifiers, which are normally of no interest to users. |
| For the rare occasions when you actually have to look at them, |
| enclose them in angle brackets to avoid the lower-case mapping. |
| For example, |
| <pre class="smallexample"> (gdb) print <JMPBUF_SAVE>[0] |
| </pre> |
| <li>Printing an object of class-wide type or dereferencing an |
| access-to-class-wide value will display all the components of the object's |
| specific type (as indicated by its run-time tag). Likewise, component |
| selection on such a value will operate on the specific type of the |
| object. |
| |
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