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