Hi,
I am new to c++. I recently spend an enormous among of time
troubleshooting a seeminly innocuous piece of code. Although I narrow
down this piece of code as the culprit but I don't understand why. Can
some guru help to enlighten me? Thank you.
// I created an array of pointers to object pointers:
Object ** obs = new Object * [9];
// After that I populate this array:
for(int i=0; i<9; i++){
obs[i] = new Object(i);
}
// After using them i deleted the array:
for(int i=0; i<9; i++){
delete obs[i];
}
delete [] obs;
delete obs; // this is the problem, during execution the program
hanged.
Apparently, the above caused undefined behaviour. But I don't know why
i shouldn't do that. Thanks again for any sharing!
Cheers,
Damon 11 1785
"DamonChong " <so********@exc ite.com> wrote in message
news:11******** *************@c 13g2000cwb.goog legroups.com... Hi,
I am new to c++. I recently spend an enormous among of time troubleshooting a seeminly innocuous piece of code. Although I narrow down this piece of code as the culprit but I don't understand why. Can some guru help to enlighten me? Thank you.
While the gurus answer more difficult questions, I'll field this one. // I created an array of pointers to object pointers:
Object ** obs = new Object * [9];
/////////// Great, you've allocated an array of pointers to Object // After that I populate this array:
for(int i=0; i<9; i++){ obs[i] = new Object(i);
/////////// And now you've allocated the objects. }
// After using them i deleted the array:
for(int i=0; i<9; i++){ delete obs[i];
/////////// Now you've deallocated the objects.
}
delete [] obs;
/////////// And now you've deallocated the array.
/////////// Good. So you've deallocated everything you've allocated. Nothing
left to deallocate.
/////////// and yet.... delete obs; // this is the problem, during execution the program hanged.
/////////// So the previous line hangs since you're deallocating something
which you shouldn't
Hi Damon
Efrat already answered your post, but I will recommend you do not use
new/delete as a newbie C++ programmer. Instead focus on the standard library
and just don't use pointers.
Pointers are difficult and better not used until you understand the basics
of C++ - including the standard library. By going this route, you will also
learn how little use there actually is of pointers in modern C++.
/Peter
"DamonChong " <so********@exc ite.com> skrev i en meddelelse
news:11******** *************@c 13g2000cwb.goog legroups.com... Hi,
I am new to c++. I recently spend an enormous among of time troubleshooting a seeminly innocuous piece of code. Although I narrow down this piece of code as the culprit but I don't understand why. Can some guru help to enlighten me? Thank you.
// I created an array of pointers to object pointers:
Object ** obs = new Object * [9];
// After that I populate this array:
for(int i=0; i<9; i++){ obs[i] = new Object(i); }
// After using them i deleted the array:
for(int i=0; i<9; i++){ delete obs[i]; }
delete [] obs;
delete obs; // this is the problem, during execution the program hanged.
Apparently, the above caused undefined behaviour. But I don't know why i shouldn't do that. Thanks again for any sharing!
Cheers, Damon
On 29 Jan 2005 01:39:32 -0800, "DamonChong " <so********@exc ite.com>
wrote: delete [] obs;
delete obs; // this is the problem, during execution the program
normally you use delete [] on any array you allocate to tell the
compiler that the ptr you are deleting is an array.
it is just one of those not obvious c++ rules you need to learn :)
in any case I would suggest you use vector<> instead of array since it
is safer and more convenient. check up the online help/book for info.
STL in general can help you a lot.
/ajk
--
"Those are my principles. If you don't like them I have others."
Groucho Marx.
Thanks alot. Kind of silly I suppose to make such mistake. ;P
"DamonChong " <so********@exc ite.com> wrote in message
news:11******** **************@ c13g2000cwb.goo glegroups.com.. . Thanks alot. Kind of silly I suppose to make such mistake. ;P
No problem. BTW, explicit memory management is both very powerful, and
very prone to making "silly" mistakes (which I don't think are silly at
all). Consequently, perhaps you might want to read Peter Koch Larsen's
response (with which I completely agree).
Specifically, you could write your code this way:
#include <vector>
std::vector<Obj ect> obs[9];
for(int i = 0; i < 9; ++i)
obs[i] = Object(i);
Or if Object doesn't have a default constructor,
#include <vector>
#include <boost/shared_ptr.hpp>
std::vector<boo st::shared_ptr< Object> > obs(9);
for(int i = 0; i < 9; ++i)
obs[i].reset(new Object(i));
(You could google for boost smart_ptr for the above).
While I would agree that pointers are maybe not obvious for a beginner to
say that there is "little use" of pointers in modern c++ is just plain wrong
in my opinion. Of course it maybe depends on what you define as "modern c++"
but that is another question...
"Peter Koch Larsen" <pk*****@mailme .dk> wrote in message
news:%j******** ************@ne ws000.worldonli ne.dk... Hi Damon
Efrat already answered your post, but I will recommend you do not use new/delete as a newbie C++ programmer. Instead focus on the standard library and just don't use pointers. Pointers are difficult and better not used until you understand the basics of C++ - including the standard library. By going this route, you will also learn how little use there actually is of pointers in modern C++.
/Peter "DamonChong " <so********@exc ite.com> skrev i en meddelelse news:11******** *************@c 13g2000cwb.goog legroups.com... Hi,
I am new to c++. I recently spend an enormous among of time troubleshooting a seeminly innocuous piece of code. Although I narrow down this piece of code as the culprit but I don't understand why. Can some guru help to enlighten me? Thank you.
// I created an array of pointers to object pointers:
Object ** obs = new Object * [9];
// After that I populate this array:
for(int i=0; i<9; i++){ obs[i] = new Object(i); }
// After using them i deleted the array:
for(int i=0; i<9; i++){ delete obs[i]; }
delete [] obs;
delete obs; // this is the problem, during execution the program hanged.
Apparently, the above caused undefined behaviour. But I don't know why i shouldn't do that. Thanks again for any sharing!
Cheers, Damon
My question is why dynamically allocate an array of Object pointers. Why not
just just
Object *obparray[9];
??
Is memory that sparse now days?
"DamonChong " <so********@exc ite.com> wrote in message
news:11******** *************@c 13g2000cwb.goog legroups.com... Hi,
I am new to c++. I recently spend an enormous among of time troubleshooting a seeminly innocuous piece of code. Although I narrow down this piece of code as the culprit but I don't understand why. Can some guru help to enlighten me? Thank you.
// I created an array of pointers to object pointers:
Object ** obs = new Object * [9];
// After that I populate this array:
for(int i=0; i<9; i++){ obs[i] = new Object(i); }
// After using them i deleted the array:
for(int i=0; i<9; i++){ delete obs[i]; }
delete [] obs;
delete obs; // this is the problem, during execution the program hanged.
Apparently, the above caused undefined behaviour. But I don't know why i shouldn't do that. Thanks again for any sharing!
Cheers, Damon
"Bradley" <bn*****@kc.rr. com> wrote in message
news:fl******** *************@t wister.rdc-kc.rr.com... My question is why dynamically allocate an array of Object pointers. Why
not just just
Object *obparray[9];
??
Is memory that sparse now days?
It's possible that Object doesn't have a default constructor.
"Efrat Regev" <ef*********@ya hoo.com> wrote in message
news:xO******** ************@ad elphia.com... "Bradley" <bn*****@kc.rr. com> wrote in message news:fl******** *************@t wister.rdc-kc.rr.com... My question is why dynamically allocate an array of Object pointers. Why
not just just
Object *obparray[9];
??
Is memory that sparse now days?
It's possible that Object doesn't have a default constructor.
Oops! my bad - I misunderstood your post. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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