📄 c-c++ memory corruption and memory leaks.mht
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Subject: C/C++ Memory Corruption And Memory Leaks
Date: Wed, 4 Apr 2007 11:10:06 +0800
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<H1>C/C++ Memory Corruption And Memory Leaks</H1>This tutorial =
will=20
discuss examples of memory leaks and code constructs which lead to =
memory=20
corruption.=20
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<TD><B><BIG>C/C++ software memory corruption=20
types:</BIG></B></TD></TR></TBODY></TABLE>
<P>There are two forms of Linux Memory accessible to the =
programmer:=20
<OL>
<LI>User's virtual memory space in which application is run.=20
<LI>Register memory. </LI></OL>
<P>The most obvious memory errors result in a "Segmentation =
violation"=20
message. This may alert the programmer to the location of the =
memory error=20
when the program is run in gdb. The following errors discussed are =
the not=20
so obvious errors.=20
<P>Memory errors:=20
<UL>
<LI>Heap memory errors:=20
<UL>
<LI>Attempting to free memory already freed.=20
<LI>Freeing memory that was not allocated.=20
<LI>Attempting to write to memory already freed.=20
<LI>Attempting to write to memory which was never allocated.=20
<LI>Memory allocation error.=20
<LI>Reading/writing to memory out of the bounds of a =
dynamically=20
allocated array </LI></UL>
<P></P>
<LI>stack (local variables) memory errors:=20
<UL>
<LI>Reading/writing to memory out of the bounds of a static =
array.=20
(array index overflow - index too large/underflow - negative =
index)=20
<LI>Function pointer corruption: Invalid passing of function =
pointer=20
and thus a bad call to a function. </LI></UL></LI></UL>
<P><A name=3DMEMORYLEAKS></A>
<HR>
<TABLE cellSpacing=3D0 cellPadding=3D2 width=3D"100%" border=3D0>
<TBODY>
<TR bgColor=3D#ffcc33>
<TD><B><BIG>Memory Leaks:</BIG></B></TD></TR></TBODY></TABLE>
<P><B>Memory leak description:</B> Memory is allocated but not =
released=20
causing an application to consume memory reducing the available =
memory for=20
other applications and eventually causing the system to page =
virtual=20
memory to the hard drive slowing the application or crashing the=20
application when than the computer memory resource limits are =
reached. The=20
system may stop working as these limits are approached.=20
<P>
<HR>
<P><B>Many C library functions malloc's memory which MUST be =
freed:</B>=20
i.e.: strdup(),=20
<DL>
<DD>
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<TD><PRE>#include <STDLIB.H>
#include <STRING.H>
...
char *oldString =3D "Old String";
char newStrig =3D strdup(oldString);
if(newString =3D=3D ENOMEM) ... // Fail!!!!
...
free(newString);
</PRE></TD></TR></TBODY></TABLE></DD></DL>Note: You can NOT use the C++=20
delete call. The strdup() function is part of the C library and =
you must=20
use free().=20
<P>Any routine which is supplied by the C libraries or ones =
written within=20
an application which allocate memory must have the memory freed. =
Comments=20
on this need should be included in the include file to make users =
of the=20
function aware of their duties to free the memory and the =
mechanism by=20
which it is to be freed (free() or delete).=20
<P>
<HR>
<P><B>Programmer must free() malloc()'ed memory:</B>=20
<P>Also for calloc(), malloc() and realloc();=20
<DL>
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