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<title>Debugging with GDB: M2 Types</title>
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<a name="M2-Types"></a>
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<div class="header">
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<p>
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Next: <a href="M2-Defaults.html#M2-Defaults" accesskey="n" rel="next">M2 Defaults</a>, Previous: <a href="M2-Constants.html#M2-Constants" accesskey="p" rel="previous">M2 Constants</a>, Up: <a href="Modula_002d2.html#Modula_002d2" accesskey="u" rel="up">Modula-2</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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<hr>
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<a name="Modula_002d2-Types"></a>
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<h4 class="subsubsection">15.4.9.4 Modula-2 Types</h4>
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<a name="index-Modula_002d2-types"></a>
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<p>Currently <small>GDB</small> can print the following data types in Modula-2
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syntax: array types, record types, set types, pointer types, procedure
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types, enumerated types, subrange types and base types. You can also
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print the contents of variables declared using these type.
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This section gives a number of simple source code examples together with
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sample <small>GDB</small> sessions.
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</p>
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<p>The first example contains the following section of code:
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</p>
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<div class="smallexample">
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<pre class="smallexample">VAR
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s: SET OF CHAR ;
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r: [20..40] ;
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</pre></div>
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<p>and you can request <small>GDB</small> to interrogate the type and value of
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<code>r</code> and <code>s</code>.
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) print s
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{'A'..'C', 'Z'}
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(gdb) ptype s
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SET OF CHAR
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(gdb) print r
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21
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(gdb) ptype r
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[20..40]
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</pre></div>
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<p>Likewise if your source code declares <code>s</code> as:
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</p>
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<div class="smallexample">
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<pre class="smallexample">VAR
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s: SET ['A'..'Z'] ;
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</pre></div>
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<p>then you may query the type of <code>s</code> by:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) ptype s
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type = SET ['A'..'Z']
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</pre></div>
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<p>Note that at present you cannot interactively manipulate set
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expressions using the debugger.
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</p>
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<p>The following example shows how you might declare an array in Modula-2
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and how you can interact with <small>GDB</small> to print its type and contents:
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</p>
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<div class="smallexample">
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<pre class="smallexample">VAR
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s: ARRAY [-10..10] OF CHAR ;
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</pre></div>
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<div class="smallexample">
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<pre class="smallexample">(gdb) ptype s
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ARRAY [-10..10] OF CHAR
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</pre></div>
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<p>Note that the array handling is not yet complete and although the type
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is printed correctly, expression handling still assumes that all
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arrays have a lower bound of zero and not <code>-10</code> as in the example
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above.
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</p>
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<p>Here are some more type related Modula-2 examples:
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</p>
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<div class="smallexample">
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<pre class="smallexample">TYPE
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colour = (blue, red, yellow, green) ;
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t = [blue..yellow] ;
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VAR
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s: t ;
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BEGIN
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s := blue ;
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</pre></div>
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<p>The <small>GDB</small> interaction shows how you can query the data type
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and value of a variable.
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) print s
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$1 = blue
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(gdb) ptype t
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type = [blue..yellow]
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</pre></div>
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<p>In this example a Modula-2 array is declared and its contents
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displayed. Observe that the contents are written in the same way as
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their <code>C</code> counterparts.
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</p>
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<div class="smallexample">
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<pre class="smallexample">VAR
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s: ARRAY [1..5] OF CARDINAL ;
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BEGIN
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s[1] := 1 ;
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</pre></div>
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<div class="smallexample">
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<pre class="smallexample">(gdb) print s
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$1 = {1, 0, 0, 0, 0}
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(gdb) ptype s
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type = ARRAY [1..5] OF CARDINAL
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</pre></div>
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<p>The Modula-2 language interface to <small>GDB</small> also understands
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pointer types as shown in this example:
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</p>
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<div class="smallexample">
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<pre class="smallexample">VAR
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s: POINTER TO ARRAY [1..5] OF CARDINAL ;
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BEGIN
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NEW(s) ;
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s^[1] := 1 ;
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</pre></div>
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<p>and you can request that <small>GDB</small> describes the type of <code>s</code>.
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) ptype s
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type = POINTER TO ARRAY [1..5] OF CARDINAL
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</pre></div>
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<p><small>GDB</small> handles compound types as we can see in this example.
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Here we combine array types, record types, pointer types and subrange
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types:
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</p>
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<div class="smallexample">
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<pre class="smallexample">TYPE
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foo = RECORD
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f1: CARDINAL ;
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f2: CHAR ;
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f3: myarray ;
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END ;
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myarray = ARRAY myrange OF CARDINAL ;
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myrange = [-2..2] ;
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VAR
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s: POINTER TO ARRAY myrange OF foo ;
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</pre></div>
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<p>and you can ask <small>GDB</small> to describe the type of <code>s</code> as shown
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below.
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) ptype s
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type = POINTER TO ARRAY [-2..2] OF foo = RECORD
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f1 : CARDINAL;
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f2 : CHAR;
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f3 : ARRAY [-2..2] OF CARDINAL;
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END
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</pre></div>
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<p>
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Next: <a href="M2-Defaults.html#M2-Defaults" accesskey="n" rel="next">M2 Defaults</a>, Previous: <a href="M2-Constants.html#M2-Constants" accesskey="p" rel="previous">M2 Constants</a>, Up: <a href="Modula_002d2.html#Modula_002d2" accesskey="u" rel="up">Modula-2</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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