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Full Discussion: Mismatch free() / delete / delete [C++]
Operating Systems Linux Mismatch free() / delete / delete [C++] Post 302985019 by Corona688 on Thursday 3rd of November 2016 06:03:06 PM
Old 11-03-2016
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 CENTOS

std::ostream_iterator

std::ostream_iterator< _Tp, _CharT, _Traits >(3)	     Library Functions Manual		  std::ostream_iterator< _Tp, _CharT, _Traits >(3)

NAME

       std::ostream_iterator< _Tp, _CharT, _Traits > -

SYNOPSIS

       Inherits std::iterator< output_iterator_tag, void, void, void, void >.

   Public Types
       typedef void difference_type
       typedef output_iterator_tag iterator_category
       typedef void pointer
       typedef void reference
       typedef void value_type

	   typedef _CharT char_type
	   typedef _Traits traits_type
	   typedef basic_ostream< _CharT,
	       _Traits > ostream_type"

   Public Member Functions
       ostream_iterator (ostream_type &__s)
       ostream_iterator (ostream_type &__s, const _CharT *__c)
       ostream_iterator (const ostream_iterator &__obj)
       ostream_iterator & operator* ()
       ostream_iterator & operator++ ()
       ostream_iterator & operator++ (int)
       ostream_iterator & operator= (const _Tp &__value)

Detailed Description
   template<typename _Tp, typename _CharT = char, typename _Traits = char_traits<_CharT>>class std::ostream_iterator< _Tp, _CharT, _Traits >
       Provides output iterator semantics for streams.

       This class provides an iterator to write to an ostream. The type Tp is the only type written by this iterator and there must be an
       operator<<(Tp) defined.

       Template Parameters:
	   _Tp The type to write to the ostream.
	   _CharT The ostream char_type.
	   _Traits The ostream char_traits.

       Definition at line 154 of file stream_iterator.h.

Member Typedef Documentation
   template<typename _Tp , typename _CharT  = char, typename _Traits  = char_traits<_CharT>> typedef _CharT std::ostream_iterator< _Tp, _CharT,
       _Traits >::char_type
       Public typedef.

       Definition at line 160 of file stream_iterator.h.

   typedef void  std::iterator< output_iterator_tag , void , void , void , void  >::difference_type [inherited]
       Distance between iterators is represented as this type.

       Definition at line 125 of file stl_iterator_base_types.h.

   typedef output_iterator_tag	std::iterator< output_iterator_tag , void , void , void , void	>::iterator_category [inherited]
       One of the tag types.

       Definition at line 121 of file stl_iterator_base_types.h.

   template<typename _Tp , typename _CharT  = char, typename _Traits  = char_traits<_CharT>> typedef basic_ostream<_CharT, _Traits>
       std::ostream_iterator< _Tp, _CharT, _Traits >::ostream_type
       Public typedef.

       Definition at line 162 of file stream_iterator.h.

   typedef void  std::iterator< output_iterator_tag , void , void , void , void  >::pointer [inherited]
       This type represents a pointer-to-value_type.

       Definition at line 127 of file stl_iterator_base_types.h.

   typedef void  std::iterator< output_iterator_tag , void , void , void , void  >::reference [inherited]
       This type represents a reference-to-value_type.

       Definition at line 129 of file stl_iterator_base_types.h.

   template<typename _Tp , typename _CharT  = char, typename _Traits  = char_traits<_CharT>> typedef _Traits std::ostream_iterator< _Tp, _CharT,
       _Traits >::traits_type
       Public typedef.

       Definition at line 161 of file stream_iterator.h.

   typedef void  std::iterator< output_iterator_tag , void , void , void , void  >::value_type [inherited]
       The type 'pointed to' by the iterator.

       Definition at line 123 of file stl_iterator_base_types.h.

Constructor &; Destructor Documentation
   template<typename _Tp , typename _CharT  = char, typename _Traits  = char_traits<_CharT>> std::ostream_iterator< _Tp, _CharT, _Traits
       >::ostream_iterator (ostream_type &__s) [inline]
       Construct from an ostream.

       Definition at line 171 of file stream_iterator.h.

   template<typename _Tp , typename _CharT  = char, typename _Traits  = char_traits<_CharT>> std::ostream_iterator< _Tp, _CharT, _Traits
       >::ostream_iterator (ostream_type &__s, const _CharT *__c) [inline]
       Construct from an ostream.

       The delimiter string c is written to the stream after every Tp written to the stream. The delimiter is not copied, and thus must not be
       destroyed while this iterator is in use.

       Parameters:
	   __s Underlying ostream to write to.
	   __c CharT delimiter string to insert.

       Definition at line 183 of file stream_iterator.h.

   template<typename _Tp , typename _CharT  = char, typename _Traits  = char_traits<_CharT>> std::ostream_iterator< _Tp, _CharT, _Traits
       >::ostream_iterator (const ostream_iterator< _Tp, _CharT, _Traits > &__obj) [inline]
       Copy constructor.

       Definition at line 187 of file stream_iterator.h.

Member Function Documentation
   template<typename _Tp , typename _CharT  = char, typename _Traits  = char_traits<_CharT>> ostream_iterator& std::ostream_iterator< _Tp, _CharT,
       _Traits >::operator= (const _Tp &__value) [inline]
       Writes value to underlying ostream using operator<<. If constructed with delimiter string, writes delimiter to ostream.

       Definition at line 193 of file stream_iterator.h.

Author
       Generated automatically by Doxygen for libstdc++ from the source code.

libstdc++							  Tue Jun 10 2014		  std::ostream_iterator< _Tp, _CharT, _Traits >(3)
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