What is the best alternative for realloc in C++

**Rolf Magnus** · Jul 22 '05, 09:01 AM

Re: What is the best alternative for realloc in C++

Kumar wrote:
[color=blue]
> Hi,
> Can somebody advise me on what is the best alternative for realloc in
> C++?[/color]

What would you need it for?
[color=blue]
> Is it safe to "realloc"at e memory allocated using new operator ?[/color]

No. You can only use realloc on memory that you got from malloc or
realloc. Also, realloc won't work properly with non-pod objects, since
it doesn't care about constructors and destructors.

**Rolf Magnus** · Jul 22 '05, 09:01 AM

Re: What is the best alternative for realloc in C++

Kumar wrote:
[color=blue]
> Hi,
> Can somebody advise me on what is the best alternative for realloc in
> C++?[/color]

What would you need it for?
[color=blue]
> Is it safe to "realloc"at e memory allocated using new operator ?[/color]

No. You can only use realloc on memory that you got from malloc or
realloc. Also, realloc won't work properly with non-pod objects, since
it doesn't care about constructors and destructors.

**David Harmon** · Jul 22 '05, 09:01 AM

Re: What is the best alternative for realloc in C++

On 6 Apr 2004 02:12:33 -0700 in comp.lang.c++, rsmkumar@acmet. com
(Kumar) wrote,[color=blue]
>Hi,
>Can somebody advise me on what is the best alternative for realloc in C++?[/color]

std::vector<>:: resize()
[color=blue]
>Is it safe to "realloc"at e memory allocated using new operator ?[/color]

Don't use 'new'.

**David Harmon** · Jul 22 '05, 09:01 AM

Re: What is the best alternative for realloc in C++

On 6 Apr 2004 02:12:33 -0700 in comp.lang.c++, rsmkumar@acmet. com
(Kumar) wrote,[color=blue]
>Hi,
>Can somebody advise me on what is the best alternative for realloc in C++?[/color]

std::vector<>:: resize()
[color=blue]
>Is it safe to "realloc"at e memory allocated using new operator ?[/color]

Don't use 'new'.

**Kevin Goodsell** · Jul 22 '05, 09:03 AM

Re: What is the best alternative for realloc in C++

Rolf Magnus wrote:
[color=blue]
> Kumar wrote:
>[color=green]
>>Is it safe to "realloc"at e memory allocated using new operator ?[/color]
>
>
> No. You can only use realloc on memory that you got from malloc or
> realloc.[/color]

....or calloc().
[color=blue]
> Also, realloc won't work properly with non-pod objects, since
> it doesn't care about constructors and destructors.
>[/color]

Likewise with malloc(), calloc(), and free(), which is why these should
only be used when absolutely necessary, and only by people who really
know what they are doing.

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

**Kevin Goodsell** · Jul 22 '05, 09:03 AM

Re: What is the best alternative for realloc in C++

Rolf Magnus wrote:
[color=blue]
> Kumar wrote:
>[color=green]
>>Is it safe to "realloc"at e memory allocated using new operator ?[/color]
>
>
> No. You can only use realloc on memory that you got from malloc or
> realloc.[/color]

....or calloc().
[color=blue]
> Also, realloc won't work properly with non-pod objects, since
> it doesn't care about constructors and destructors.
>[/color]

Likewise with malloc(), calloc(), and free(), which is why these should
only be used when absolutely necessary, and only by people who really
know what they are doing.

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

**Kevin Goodsell** · Jul 22 '05, 09:03 AM

Re: What is the best alternative for realloc in C++

David Harmon wrote:
[color=blue]
>
> Don't use 'new'.
>[/color]

Reasonable advice, but just to be perfectly clear:

1) Don't use malloc() (and friends) when 'new' can do the job.

2) Don't use malloc() or 'new' when containers or automatic variables
can do the job.

3) When explicit memory management is necessary, try to use smart
pointers to make it easier and safer.

4) If you do have to use any form of explicit memory management, use
caution.

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

**Kevin Goodsell** · Jul 22 '05, 09:03 AM

Re: What is the best alternative for realloc in C++

David Harmon wrote:
[color=blue]
>
> Don't use 'new'.
>[/color]

Reasonable advice, but just to be perfectly clear:

1) Don't use malloc() (and friends) when 'new' can do the job.

2) Don't use malloc() or 'new' when containers or automatic variables
can do the job.

3) When explicit memory management is necessary, try to use smart
pointers to make it easier and safer.

4) If you do have to use any form of explicit memory management, use
caution.

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

**Evan Carew** · Jul 22 '05, 09:03 AM

Re: What is the best alternative for realloc in C++

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Kumar wrote:[color=blue]
> Hi,
> Can somebody advise me on what is the best alternative for realloc in C++?
> Is it safe to "realloc"at e memory allocated using new operator ?[/color]
Kumar,

The simple answer is that realloc is nothing more than a fancy version
of malloc, ie new. So if you are working with STL compliant objects &
containers, then simply setting one equal to another will suffice, then
either let the old object go out of scope (if automatic), or delete it.

Evan
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**Evan Carew** · Jul 22 '05, 09:03 AM

Re: What is the best alternative for realloc in C++

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Kumar wrote:[color=blue]
> Hi,
> Can somebody advise me on what is the best alternative for realloc in C++?
> Is it safe to "realloc"at e memory allocated using new operator ?[/color]
Kumar,

The simple answer is that realloc is nothing more than a fancy version
of malloc, ie new. So if you are working with STL compliant objects &
containers, then simply setting one equal to another will suffice, then
either let the old object go out of scope (if automatic), or delete it.

Evan
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**Kevin Goodsell** · Jul 22 '05, 09:03 AM

Re: What is the best alternative for realloc in C++

Evan Carew wrote:[color=blue]
> malloc, ie new.[/color]

The implication that malloc() and 'new' are equivalent is very wrong.
There are significant differences, for example: malloc() returns NULL on
failure while 'new' throws an exception, malloc() allocates raw memory
while 'new' constructs objects in the allocated space, malloc() is a
single function while 'new' comes in several variants and can be
overloaded or overridden by the programmer.

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

**Kevin Goodsell** · Jul 22 '05, 09:03 AM

Re: What is the best alternative for realloc in C++

Evan Carew wrote:[color=blue]
> malloc, ie new.[/color]

The implication that malloc() and 'new' are equivalent is very wrong.
There are significant differences, for example: malloc() returns NULL on
failure while 'new' throws an exception, malloc() allocates raw memory
while 'new' constructs objects in the allocated space, malloc() is a
single function while 'new' comes in several variants and can be
overloaded or overridden by the programmer.

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

**Evan Carew** · Jul 22 '05, 09:05 AM

Re: What is the best alternative for realloc in C++

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Kumar,

I'm sure Kevin means well, but I think you would do well to put his
posts in your filter list. The problem with his post is that most
compiler vendors do indeed use malloc under the hood as the default new
operator's machenery. While many vendors do add additional functionality
to new beside what malloc provides, ultimately, you are interfacing with
the OS's memory machenery, and thus must use its entry points. In the
UNIX world, this happens to be malloc (I can't imagine it would be any
different with MS products).

Evan Carew
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**Evan Carew** · Jul 22 '05, 09:05 AM

Re: What is the best alternative for realloc in C++

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Kumar,

I'm sure Kevin means well, but I think you would do well to put his
posts in your filter list. The problem with his post is that most
compiler vendors do indeed use malloc under the hood as the default new
operator's machenery. While many vendors do add additional functionality
to new beside what malloc provides, ultimately, you are interfacing with
the OS's memory machenery, and thus must use its entry points. In the
UNIX world, this happens to be malloc (I can't imagine it would be any
different with MS products).

Evan Carew
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