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| <title>Debugging with GDB: M2 Types</title> |
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| <a name="M2-Types"></a> |
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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="prev">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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| <a name="Modula_002d2-Types"></a> |
| <h4 class="subsubsection">15.4.8.4 Modula-2 Types</h4> |
| <a name="index-Modula_002d2-types"></a> |
| |
| <p>Currently <small>GDB</small> can print the following data types in Modula-2 |
| syntax: array types, record types, set types, pointer types, procedure |
| types, enumerated types, subrange types and base types. You can also |
| print the contents of variables declared using these type. |
| This section gives a number of simple source code examples together with |
| sample <small>GDB</small> sessions. |
| </p> |
| <p>The first example contains the following section of code: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">VAR |
| s: SET OF CHAR ; |
| r: [20..40] ; |
| </pre></div> |
| |
| <p>and you can request <small>GDB</small> to interrogate the type and value of |
| <code>r</code> and <code>s</code>. |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) print s |
| {'A'..'C', 'Z'} |
| (gdb) ptype s |
| SET OF CHAR |
| (gdb) print r |
| 21 |
| (gdb) ptype r |
| [20..40] |
| </pre></div> |
| |
| <p>Likewise if your source code declares <code>s</code> as: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">VAR |
| s: SET ['A'..'Z'] ; |
| </pre></div> |
| |
| <p>then you may query the type of <code>s</code> by: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) ptype s |
| type = SET ['A'..'Z'] |
| </pre></div> |
| |
| <p>Note that at present you cannot interactively manipulate set |
| expressions using the debugger. |
| </p> |
| <p>The following example shows how you might declare an array in Modula-2 |
| and how you can interact with <small>GDB</small> to print its type and contents: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">VAR |
| s: ARRAY [-10..10] OF CHAR ; |
| </pre></div> |
| |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) ptype s |
| ARRAY [-10..10] OF CHAR |
| </pre></div> |
| |
| <p>Note that the array handling is not yet complete and although the type |
| is printed correctly, expression handling still assumes that all |
| arrays have a lower bound of zero and not <code>-10</code> as in the example |
| above. |
| </p> |
| <p>Here are some more type related Modula-2 examples: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">TYPE |
| colour = (blue, red, yellow, green) ; |
| t = [blue..yellow] ; |
| VAR |
| s: t ; |
| BEGIN |
| s := blue ; |
| </pre></div> |
| |
| <p>The <small>GDB</small> interaction shows how you can query the data type |
| and value of a variable. |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) print s |
| $1 = blue |
| (gdb) ptype t |
| type = [blue..yellow] |
| </pre></div> |
| |
| <p>In this example a Modula-2 array is declared and its contents |
| displayed. Observe that the contents are written in the same way as |
| their <code>C</code> counterparts. |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">VAR |
| s: ARRAY [1..5] OF CARDINAL ; |
| BEGIN |
| s[1] := 1 ; |
| </pre></div> |
| |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) print s |
| $1 = {1, 0, 0, 0, 0} |
| (gdb) ptype s |
| type = ARRAY [1..5] OF CARDINAL |
| </pre></div> |
| |
| <p>The Modula-2 language interface to <small>GDB</small> also understands |
| pointer types as shown in this example: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">VAR |
| s: POINTER TO ARRAY [1..5] OF CARDINAL ; |
| BEGIN |
| NEW(s) ; |
| s^[1] := 1 ; |
| </pre></div> |
| |
| <p>and you can request that <small>GDB</small> describes the type of <code>s</code>. |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) ptype s |
| type = POINTER TO ARRAY [1..5] OF CARDINAL |
| </pre></div> |
| |
| <p><small>GDB</small> handles compound types as we can see in this example. |
| Here we combine array types, record types, pointer types and subrange |
| types: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">TYPE |
| foo = RECORD |
| f1: CARDINAL ; |
| f2: CHAR ; |
| f3: myarray ; |
| END ; |
| |
| myarray = ARRAY myrange OF CARDINAL ; |
| myrange = [-2..2] ; |
| VAR |
| s: POINTER TO ARRAY myrange OF foo ; |
| </pre></div> |
| |
| <p>and you can ask <small>GDB</small> to describe the type of <code>s</code> as shown |
| below. |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) ptype s |
| type = POINTER TO ARRAY [-2..2] OF foo = RECORD |
| f1 : CARDINAL; |
| f2 : CHAR; |
| f3 : ARRAY [-2..2] OF CARDINAL; |
| END |
| </pre></div> |
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