Re: C++ - Pointer to Structure leads to segfault

=?UTF-8?B?RXJpayBXaWtzdHLDtm0=?= <>
Tue, 13 Jan 2009 21:37:00 GMT
On 2009-01-13 22:18, dmangal wrote:

Hi all...first time poster, long time reader.

I've been experiencing some strange behavior on a Linux development
system (Red Hat 5) compiling a C++ App. I've tried to reduce the
source to something as simple as possible so that I can fit all source
that would still causes my problem. Below are the three simple source
files for class FooClass:

class FooClass
     void fooMethod();
     typedef struct {
          int fooData;
     } FooStruct;

C-ism, in C++ you don't need the typedef:

struct FooStruct {
  int fooData;

#include "FooClass.hpp"

void FooClass::fooMethod()
     FooStruct* foo;

You create a pointer to a FooStruct, but you do not initialise it to
anything, so it could point to just about anything.

     foo->fooData = 5;

And here you take the piece of memory that the pointer happens to point
to and try to treat it as if it pointed to a FooStruct object.

You forgot to initialise the pointer, replace the FooStruct* foo; line
with this:

  FooStruct* foo = new FooStruct();

Oh...and for a side note, this runs with no problem on a different
system running an older version of Linux (Red Hat 4).

Just luck. I suppose a change in RH5 caused to pointer to be initialised
to a different value which happens to point to a unallocated address
while in RH4 you were lucky and the pointer pointed to some allocated

Erik Wikstr??m

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