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      <DIV class="header-title">
      The C++ Debugging Support Library
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      By Carlo Wood, &copy;1999 - 2003.
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<DIV class="body">

<H2>Tutorial 7: Advanced examples</H2>

<P>In this tutorial you will learn how to make memory allocations
&laquo;invisible&raquo; so that they will not show up in the
Allocated memory Overview, how to find information about an
allocated memory block given an arbitrary pointer pointing
inside it and how to write simple memory-leak detection code.</P>

<A NAME="Removing"></A>
<H3>7.1 Removing allocations from the Allocated memory Overview</H3>

<P>Sometimes a program can allocate a very large number of memory blocks.&nbsp;
Having all of those in the Allocated memory Overview could make it
impractically large.&nbsp; Therefore it is possible to remove items from this list.</P>

<P>In the following example we make one allocation invisible by
using the function <CODE>make_invisible()</CODE>:</P>

<P>Compile as: <CODE>g++ -g -DCWDEBUG test7.1.1.cc -lcwd -o invisible</CODE></P>
<P class="download">[<A HREF="examples7/test7.1.1.cc">download</A>]</P>
<PRE>
<!-- START CODE examples7/test7.1.1.cc -->
#include &quot;sys.h&quot;
#include &quot;debug.h&quot;

int main(void)
{
  Debug( libcw_do.on() );
  Debug( dc::malloc.on() );

  int* first = new int;
  AllocTag2(first, &quot;first&quot;);

  int* second = new int;
  AllocTag2(second, &quot;second&quot;);

  Debug( list_allocations_on(libcw_do) );

  Debug( <SPAN class="highlight">make_invisible(</SPAN>first<SPAN class="highlight">)</SPAN> );

  Debug( list_allocations_on(libcw_do) );

  delete second;
  delete first;

  return 0;
}
<!-- END CODE examples7/test7.1.1.cc -->
</PRE>

<P>The output of this program is</P>

<PRE class="output">
<!-- START OUTPUT examples7/test7.1.1-bin -->
MALLOC  : operator new (size = 4) = 0x6b7ec0 [test7.1.1.cc:9]
MALLOC  : operator new (size = 4) = 0x7f56e0 [test7.1.1.cc:12]
MALLOC  : Allocated memory: 8 bytes in 2 blocks.
          0x7f56e0         test7.1.1.cc:12   int; (sz = 4)  second
          0x6b7ec0         test7.1.1.cc:9    int; (sz = 4)  first
MALLOC  : Allocated memory: 4 bytes in 1 blocks.
          0x7f56e0         test7.1.1.cc:12   int; (sz = 4)  second
MALLOC  : delete 0x7f56e0         test7.1.1.cc:12   int; (sz = 4)  second 
</PRE>

<P>As you can see, the first allocation at line 9 disappeared from the
overview after it was made invisible.</P>

<P>Pointer validation at de-allocation is still performed however.&nbsp;
For instance, when we make a mistake when freeing the first <CODE>int</CODE>:</P>

<P>Compile as: <CODE>g++ -g -DCWDEBUG test7.1.2.cc -lcwd -o coredump</CODE></P>
<P class="download">[<A HREF="examples7/test7.1.2.cc">download</A>]</P>
<PRE>
<!-- START CODE examples7/test7.1.2.cc -->
#include &quot;sys.h&quot;
#include &quot;debug.h&quot;

int main(void)
{
  Debug( libcw_do.on() );
  Debug( dc::malloc.on() );

  int* first = new int;
  AllocTag2(first, &quot;first&quot;);

  int* second = new int;
  AllocTag2(second, &quot;second&quot;);

  Debug( list_allocations_on(libcw_do) );

  Debug( make_invisible(first) );

  Debug( list_allocations_on(libcw_do) );

  delete second;
  delete <SPAN class="highlight">[]</SPAN> first;	// Make a deliberate error

  return 0;
}
<!-- END CODE examples7/test7.1.2.cc -->
</PRE>

<P>then the output becomes</P>

<PRE class="output">
<!-- START OUTPUT examples7/test7.1.2-bin -->
MALLOC  : operator new (size = 4) = 0x6e6410 [test7.1.2.cc:9]
MALLOC  : operator new (size = 4) = 0x7f5780 [test7.1.2.cc:12]
MALLOC  : Allocated memory: 8 bytes in 2 blocks.
          0x7f5780         test7.1.2.cc:12   int; (sz = 4)  second
          0x6e6410         test7.1.2.cc:9    int; (sz = 4)  first
MALLOC  : Allocated memory: 4 bytes in 1 blocks.
          0x7f5780         test7.1.2.cc:12   int; (sz = 4)  second
MALLOC  : delete 0x7f5780         test7.1.2.cc:12   int; (sz = 4)  second 
COREDUMP: You are `delete[]'-ing a block that was allocated with `new'!  Use `delete' instead.
</PRE>

<P>Also the function <CODE>test_delete()</CODE> still works:</P>

<P>Compile as: <CODE>g++ -g -DCWDEBUG test7.1.3.cc -lcwd -o test_delete</CODE></P>
<P class="download">[<A HREF="examples7/test7.1.3.cc">download</A>]</P>
<PRE>
<!-- START CODE examples7/test7.1.3.cc -->
#include &quot;sys.h&quot;
#include &quot;debug.h&quot;

int main(void)
{
  Debug( libcw_do.on() );
  Debug( dc::malloc.on() );
  Debug( dc::notice.on() );

  void* p = malloc(3000);
  
  Debug( make_invisible(p) );
  Debug( list_allocations_on(libcw_do) );

  Dout(dc::notice, &quot;test_delete(&quot; &lt;&lt; p &lt;&lt; &quot;) = &quot; &lt;&lt; <SPAN class="highlight">test_delete(</SPAN>p<SPAN class="highlight">)</SPAN>);
  free(p);
  Dout(dc::notice, &quot;test_delete(&quot; &lt;&lt; p &lt;&lt; &quot;) = &quot; &lt;&lt; <SPAN class="highlight">test_delete(</SPAN>p<SPAN class="highlight">)</SPAN>);

  return 0;
}
<!-- END CODE examples7/test7.1.3.cc -->
</PRE>

<P>results in</P>

<PRE class="output">
<!-- START OUTPUT examples7/test7.1.3-bin -->
MALLOC  : malloc(3000) = 0x7f79a0 [test7.1.3.cc:10]
MALLOC  : Allocated memory: 0 bytes in 0 blocks.
NOTICE  : test_delete(0x7f79a0) = 0
NOTICE  : test_delete(0x7f79a0) = 1
</PRE>

<P>However, <CODE>find_alloc()</CODE>, the function that is explained in the next paragraph,
will <EM>fail</EM> to find an &laquo;invisible&raquo; block (it will return <CODE>NULL</CODE>).</P>

<A NAME="Retrieving"></A>
<H3>7.2 Retrieving information about memory allocations</H3>

<P>Libcwd allows the developer to generate powerful debugging output; aside from being able to test
if a given pointer points to the start of an allocated memory block, using <CODE>test_delete()</CODE>,
it is even possible to find all information about an allocated memory block that is also shown in the Allocated memory Overview
when given a pointer pointing anywhere <EM>inside</EM> an allocated memory block.&nbsp; For example:</P>

<P>Compile as: <CODE>g++ -g -DCWDEBUG test7.2.1.cc -lcwd -o find_alloc</CODE></P>
<P class="download">[<A HREF="examples7/test7.2.1.cc">download</A>]</P>
<PRE>
<!-- START CODE examples7/test7.2.1.cc -->
#include &quot;sys.h&quot;
#include &quot;debug.h&quot;

using namespace libcwd;

template&lt;typename T1, typename T2&gt;
  struct Foo {
    T1 for_me;
    T2 for_you;
    double d;
  };

int main(void)
{
  Debug( libcw_do.on() );
  Debug( dc::malloc.on() );
  Debug( dc::notice.on() );

  Foo&lt;char, int&gt;* f = new Foo&lt;char, int&gt;;
  AllocTag(f, &quot;Our test object&quot;);

  int* p = &amp;f-&gt;for_you;	// Pointer that points inside `f'

  Dout(dc::notice, &quot;f == &quot; &lt;&lt; static_cast&lt;void*&gt;(f));
  Dout(dc::notice, &quot;p == &quot; &lt;&lt; static_cast&lt;void*&gt;(p));

#ifdef CWDEBUG
  alloc_ct const* alloc = <SPAN class="highlight">find_alloc(</SPAN>p<SPAN class="highlight">)</SPAN>;
  Dout(dc::notice,
	 &quot;p points inside \&quot;&quot;
      &lt;&lt; <SPAN class="highlight">alloc-&gt;description()</SPAN>
      &lt;&lt; &quot;\&quot; starting at &quot;
      &lt;&lt; <SPAN class="highlight">alloc-&gt;start()</SPAN>
      &lt;&lt; &quot; with size &quot;
      &lt;&lt; <SPAN class="highlight">alloc-&gt;size()</SPAN>
      &lt;&lt; '.');
  Dout(dc::notice,
	 &quot;This memory block contains a \&quot;&quot;
      &lt;&lt; <SPAN class="highlight">alloc-&gt;type_info().demangled_name()</SPAN> &lt;&lt; &quot;\&quot;.&quot;);
  Dout(dc::notice,
	 &quot;The allocation type is `&quot;
      &lt;&lt; <SPAN class="highlight">alloc-&gt;memblk_type()</SPAN>
      &lt;&lt; &quot;' and was allocated at &quot;
      &lt;&lt; <SPAN class="highlight">alloc-&gt;location()</SPAN>
      &lt;&lt; '.');
#endif

  return 0;
}
<!-- END CODE examples7/test7.2.1.cc -->
</PRE>

<P>The output of this program is</P>

<PRE class="output">
<!-- START OUTPUT examples7/test7.2.1-bin -->
MALLOC  : operator new (size = 16) = 0x634540 [test7.2.1.cc:19]
NOTICE  : f == 0x634540
NOTICE  : p == 0x634544
NOTICE  : p points inside &quot;Our test object&quot; starting at 0x634540 with size 16.
NOTICE  : This memory block contains a &quot;Foo&lt;char, int&gt;*&quot;.
NOTICE  : The allocation type is `memblk_type_new' and was allocated at test7.2.1.cc:19.
</PRE>

<P>Note that the <EM>type</EM> returned by <CODE>alloc-&gt;type_info().demangled_name()</CODE> is
the type of the pointer passed to <CODE>AllocTag()</CODE>:
This string will always end on a <CODE>'*'</CODE>.&nbsp;</P>

<P>The original reason for supporting pointers that point <EM>inside</EM> a memory block
and not just to the start of it, was so that it could be used in base classes of objects
derived with multiple inheritance: <CODE>find_alloc(this)</CODE> will
always return the correct memory block, even if there is an offset between <CODE>this</CODE>
and the real start of the allocated block.&nbsp;
The same holds for arrays of objects allocated with <CODE>new[]</CODE>.</P>

<P>It is also possible to get the values for the number of bytes and blocks allocated
in total, as is printed at the top of each Allocated memory Overview.&nbsp;
See the next paragraph.</P>

<A NAME="Memory"></A>
<H3>7.3 Memory leak detection</H3>

<P><CODE>mem_blocks()</CODE> and <CODE>mem_size()</CODE>
(like everything else defined in namespace <CODE>libcwd</CODE>)
can be used to write a very simply memory leak detection system:</P>

<P>Compile as: <CODE>g++ -g -DCWDEBUG test7.3.1.cc -lcwd -o total_alloc</CODE></P>
<P class="download">[<A HREF="examples7/test7.3.1.cc">download</A>]</P>
<PRE>
<!-- START CODE examples7/test7.3.1.cc -->
#include &quot;sys.h&quot;
#include &quot;debug.h&quot;

using namespace libcwd;

int main(void)
{
  Debug( libcw_do.on() );
  Debug( dc::malloc.on() );

  char* memory_leak = new char [300];
  AllocTag(memory_leak, "memory_leak");

  // Debug( make_invisible(memory_leak) );

#ifdef CWDEBUG
  if (<SPAN class="highlight">mem_blocks()</SPAN> &gt; 0)
    Dout(dc::warning, &quot;There are still &quot; &lt;&lt; <SPAN class="highlight">mem_size()</SPAN> &lt;&lt; &quot; bytes allocated!&quot;);
  else
    Dout(dc::malloc, &quot;No memory leaks.&quot;);
#endif

  return 0;
}
<!-- END CODE examples7/test7.3.1.cc -->
</PRE>

<P>The output of this program is:</P>

<PRE class="output">
<!-- START OUTPUT examples7/test7.3.1-bin -->
MALLOC  : operator new[] (size = 300) = 0x62bdc0 [test7.3.1.cc:11]
WARNING : There are still 300 bytes allocated!
</PRE>

<P>Invisible blocks are <B>not</B> detected!&nbsp;
When you comment out the <CODE>Debug( make_invisible(memory_leak) );</CODE> then
the output will read</P>

<PRE class="output">
MALLOC  : operator new[] (size = 300) = 0x804fc88
MALLOC  : No memory leaks.
</PRE>

<P>This allows you to improve the memory leak detection a bit in the case
of global objects that allocate memory.&nbsp; Nevertheless, that is bad
coding: you shouldn't define global objects that allocate memory.</P>

<P>Here is an example program anyway:</P>

<P>Compile as: <CODE>g++ -g -DCWDEBUG test7.3.2.cc -lcwd -o memleak</CODE></P>
<P class="download">[<A HREF="examples7/test7.3.2.cc">download</A>]</P>
<PRE>
<!-- START CODE examples7/test7.3.2.cc -->
#include &quot;sys.h&quot;
#include &quot;debug.h&quot;

class A {
private:
  char* dynamic_memory;
public:
  A(void)
  {
    dynamic_memory = new char [300];
    AllocTag(dynamic_memory, "A::dynamic_memory");
  }
  ~A()
  {
    if (dynamic_memory)
      delete [] dynamic_memory;
  }
};

// Global object that allocates memory (bad programming!)
A a;

int main(void)
{
  Debug( libcw_do.on() );
  Debug( dc::malloc.on() );

#ifdef CWDEBUG
  if (libcwd::mem_blocks() &gt; 0)
  {
    Dout(dc::malloc|dc::warning, &quot;Memory leak&quot;);
    Debug( list_allocations_on(libcw_do) );
  }
  else
    Dout(dc::malloc, &quot;No memory leaks.&quot;);
#endif

  return 0;
}
<!-- END CODE examples7/test7.3.2.cc -->
</PRE>

<P>results in</P>

<PRE class="output">
<!-- START OUTPUT examples7/test7.3.2-bin -->
MALLOC  : Memory leak
MALLOC  : Allocated memory: 300 bytes in 1 blocks.
new[]     0x7bc420         test7.3.2.cc:10   char[300]; (sz = 300)  A::dynamic_memory
MALLOC  : delete[] 0x7bc420         test7.3.2.cc:10   char[300]; (sz = 300)  A::dynamic_memory 
</PRE>

<P>simply because <CODE>A::dynamic_memory</CODE> is not deleted until <EM>after</EM> <CODE>main</CODE>.</P>

<P>A simple kludge is to make all memory allocated <EM>before</EM> <CODE>main</CODE>, invisible:</P>

<P>Compile as: <CODE>g++ -g -DCWDEBUG test7.3.3.cc -lcwd -o memleak2</CODE></P>
<P class="download">[<A HREF="examples7/test7.3.3.cc">download</A>]</P>
<PRE>
<!-- START CODE examples7/test7.3.3.cc -->
#include &quot;sys.h&quot;
#include &quot;debug.h&quot;

class A {
private:
  char* dynamic_memory;
public:
  A(void)
  {
    dynamic_memory = new char [300];
    AllocTag(dynamic_memory, "A::dynamic_memory");
  }
  ~A()
  {
    if (dynamic_memory)
      delete [] dynamic_memory;
  }
};

// Global object that allocates memory (bad programming!)
A a;

int main(void)
{
  <SPAN class="highlight">Debug( make_all_allocations_invisible_except(NULL) );</SPAN>

  Debug( libcw_do.on() );
  Debug( dc::malloc.on() );

#ifdef CWDEBUG
  if (libcwd::mem_blocks() &gt; 0)
  {
    Dout(dc::malloc|dc::warning, &quot;Memory leak&quot;);
    Debug( list_allocations_on(libcw_do) );
  }
  else
    Dout(dc::malloc, &quot;No memory leaks.&quot;);
#endif

  return 0;
}
<!-- END CODE examples7/test7.3.3.cc -->
</PRE>

<P>which will simply output</P>

<PRE class="output">
<!-- START OUTPUT examples7/test7.3.3-bin -->
MALLOC  : No memory leaks.
</PRE>

<P>Libcwd provides an alternative way to check for memory leaks using so called &laquo;markers&raquo;.&nbsp;
A marker is like a directory, any allocation made after a marker is created is put into that directory.&nbsp;
When a marker is removed and there are still allocation inside it, you will get a warning!&nbsp;
In the following example we allocate a memory block, then set a marker and next allocate two more memory
blocks.&nbsp The Allocated memory Overview is then printed.</P>

<P>Compile as: <CODE>g++ -g -DCWDEBUG test7.3.4.cc -lcwd -o marker</CODE></P>
<P class="download">[<A HREF="examples7/test7.3.4.cc">download</A>]</P>
<PRE>
<!-- START CODE examples7/test7.3.4.cc -->
#include &quot;sys.h&quot;
#include &quot;debug.h&quot;

int main(void)
{
  Debug( make_all_allocations_invisible_except(NULL) );
  Debug( libcw_do.on() );
  Debug( dc::malloc.on() );

  int* p1 = new int [10];
  AllocTag(p1, &quot;p1&quot;);

<SPAN class="highlight">#if CWDEBUG_MARKER</SPAN>
  <SPAN class="highlight">libcwd::marker_ct* marker = new libcwd::marker_ct(&quot;A test marker&quot;);</SPAN>
<SPAN class="highlight">#endif</SPAN>

  int* p2 = new int [20];
  AllocTag(p2, &quot;p2&quot;);

  int* p3 = new int [30];
  AllocTag(p3, &quot;p3&quot;);

  Debug( list_allocations_on(libcw_do) );

<SPAN class="highlight">#if CWDEBUG_MARKER</SPAN>
  // Delete the marker while there are still allocations inside it
  <SPAN class="highlight">delete marker;</SPAN>
<SPAN class="highlight">#endif</SPAN>

  return 0;
}
<!-- END CODE examples7/test7.3.4.cc -->
</PRE>

<P>The output of this program is:</P>

<PRE class="output">
<!-- START OUTPUT examples7/test7.3.4-bin -->
MALLOC  : operator new[] (size = 40) = 0x615300 [test7.3.4.cc:10]
MALLOC  : operator new (size = 16) = 0x62bd20 [test7.3.4.cc:14]
MALLOC  : New libcwd::marker_ct at 0x62bd20
MALLOC  : operator new[] (size = 80) = 0x80e3f0 [test7.3.4.cc:17]
MALLOC  : operator new[] (size = 120) = 0x80e580 [test7.3.4.cc:20]
MALLOC  : Allocated memory: 256 bytes in 4 blocks.
(MARKER)  0x62bd20         test7.3.4.cc:14   &lt;marker&gt;; (sz = 16)  A test marker
    new[]     0x80e580         test7.3.4.cc:20   int[30]; (sz = 120)  p3
    new[]     0x80e3f0         test7.3.4.cc:17   int[20]; (sz = 80)  p2
new[]     0x615300         test7.3.4.cc:10   int[10]; (sz = 40)  p1
MALLOC  : Removing libcwd::marker_ct at 0x62bd20 (A test marker)
  * WARNING : Memory leak detected!
  * new[]     0x80e580         test7.3.4.cc:20   int[30]; (sz = 120)  p3
  * new[]     0x80e3f0         test7.3.4.cc:17   int[20]; (sz = 80)  p2
MALLOC  : delete 0x62bd20         test7.3.4.cc:14   &lt;marker&gt;; (sz = 16)  A test marker 
</PRE>

<P>Individual allocations (or other markers, inclusive everything they contain)
can be moved outside a marker with the function <CODE>move_outside()</CODE>.&nbsp;
For example, we could move the allocation of <CODE>p2</CODE> outside our marker:</P>

<P>Compile as: <CODE>g++ -g -DCWDEBUG test7.3.5.cc -lcwd -o marker2</CODE></P>
<P class="download">[<A HREF="examples7/test7.3.5.cc">download</A>]</P>
<PRE>
<!-- START CODE examples7/test7.3.5.cc -->
#include &quot;sys.h&quot;
#include &quot;debug.h&quot;

int main(void)
{
  Debug( make_all_allocations_invisible_except(NULL) );
  Debug( libcw_do.on() );
  Debug( dc::malloc.on() );

  int* p1 = new int [10];
  AllocTag(p1, &quot;p1&quot;);

#if CWDEBUG_MARKER
  libcwd::marker_ct* marker = new libcwd::marker_ct(&quot;A test marker&quot;);
#endif

  int* p2 = new int [20];
  AllocTag(p2, &quot;p2&quot;);

  int* p3 = new int [30];
  AllocTag(p3, &quot;p3&quot;);

<SPAN class="highlight">#if CWDEBUG_MARKER</SPAN>
  <SPAN class="highlight">Debug( move_outside(marker, p2) );</SPAN>
<SPAN class="highlight">#endif</SPAN>

  Debug( list_allocations_on(libcw_do) );

#if CWDEBUG_MARKER
  // Delete the marker while there are still allocations inside it
  delete marker;
#endif

  return 0;
}
<!-- END CODE examples7/test7.3.5.cc -->
</PRE>

<P>which results in the output</P>

<PRE class="output">
<!-- START OUTPUT examples7/test7.3.5-bin -->
MALLOC  : operator new[] (size = 40) = 0x615300 [test7.3.5.cc:10]
MALLOC  : operator new (size = 16) = 0x62bdb0 [test7.3.5.cc:14]
MALLOC  : New libcwd::marker_ct at 0x62bdb0
MALLOC  : operator new[] (size = 80) = 0x80e490 [test7.3.5.cc:17]
MALLOC  : operator new[] (size = 120) = 0x80e620 [test7.3.5.cc:20]
MALLOC  : Allocated memory: 256 bytes in 4 blocks.
new[]     0x80e490         test7.3.5.cc:17   int[20]; (sz = 80)  p2
(MARKER)  0x62bdb0         test7.3.5.cc:14   &lt;marker&gt;; (sz = 16)  A test marker
    new[]     0x80e620         test7.3.5.cc:20   int[30]; (sz = 120)  p3
new[]     0x615300         test7.3.5.cc:10   int[10]; (sz = 40)  p1
MALLOC  : Removing libcwd::marker_ct at 0x62bdb0 (A test marker)
  * WARNING : Memory leak detected!
  * new[]     0x80e620         test7.3.5.cc:20   int[30]; (sz = 120)  p3
MALLOC  : delete 0x62bdb0         test7.3.5.cc:14   &lt;marker&gt;; (sz = 16)  A test marker 
</PRE>


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