Mismatch free() / delete / delete [C++] Post: 302985019

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Operating Systems Linux Mismatch free() / delete / delete [C++] Post 302985019 by Corona688 on Thursday 3rd of November 2016 06:03:06 PM

11-03-2016

Registered User

Quote:

Originally Posted by SA_Palani

You are right that send is to alter the value of Struct p1.

Changing its contents won't cause a crash.

You actually can't typecast things in the way you show in your example, which leaves me more and more curious to what you're actually doing.

That it's passed as a * & gives it the ability to reach in and mangle p1 itself - the pointer.

What I mean is this:

Code:

#include <iostream>
using namespace std;

void mangle_pointer(char * & x) {
        // Set the pointer to a blatantly wrong value
        x = (char *)123456789;
}

int main(void) {
        char *mem=new char;

        cerr << "mem is " << (unsigned long)mem << endl;

        mangle_pointer(mem);

        cerr << "mem is now "<< (unsigned long)mem <<
          " and will crash when deleted" << endl;

        delete mem; // Deleting any value that you didn't get from new is bad
}

This is a trivial example. Tracking down memory crashes is usually a lot harder, the crash is generally a side-effect of an overrun which stomped on the values of your variables or some important hidden values inside the heap itself. An overrun can leap straight through rational boundaries and stomp on whatever happens to be next to it in memory, with no regard for the line order of your program. If the overrun happened to something in a local variable, this can corrupt other local variables, or corrupt your return vector and cause a crash next time you return from any function. If it happened in the heap, it can corrupt other things you have stored in the heap, or corrupt the heap itself, causing delete to mess up in strange ways the next time you delete anything.

This is to say, "delete myvariable" crashing often has nothing to do with "myvariable". Debris can land far away from an explosion.

Last edited by Corona688; 11-03-2016 at 07:12 PM..

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LEARN ABOUT HPUX

delete_directory

delete directory(1m)													      delete directory(1m)

NAME

       delete directory - Deletes a directory

SYNOPSIS

       cdscp delete directory directory-name

ARGUMENTS

       The full name of the directory.

DESCRIPTION

       The  delete  directory  command	deletes a directory.  The directory cannot contain any object entries, soft links, or child pointers.  The
       master replica must be the only remaining replica in the cell.  Use the delete replica command if you need to remove read-only replicas.

   Privilege Required
       You must have delete permission to the directory and write permission to the clearinghouse that stores the master replica of the directory.
       The  server  principal  needs  administer  permission  to the parent directory or delete permission to the child pointer that points to the
       directory you intend to delete.

NOTE

       This command is replaced at Revision 1.1 by the dcecp command and may not be provided in future releases of DCE.

EXAMPLE

       The following command deletes the directory /.:/eng from the namespace: cdscp> delete directory /.:/eng

RELATED INFORMATION

       Commands: create directory(1m), delete replica(1m), list directory(1m), set directory(1m), set directory to skulk(1m), show directory(1m)

															      delete directory(1m)

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