Is there a problem using malloc and new together?

[sapird]

Hi,
I try to solve a problem in a C++ code I did not write:
When I run the application I get a memory problem, and the message says that memory was allocated with new and ran over with malloc.
Is this really the problem, or is it a simptom for something else?
Is there a known problem with using new and malloc in the same application?
Another note: the problem appears only when compiled with debug information.
The application runs under OS/2 operating system.

The relevant parts of the code:

void *d_area;
int dsize=10;
d_area = malloc (dsize);
--------
char *penv = getenv ("xxxx");
char *grp;
grp = new char (sizeof (penv) + 1);

Please note that this is only the suspected lines, and the statement int dsize=10; and similar are only shown here for understanding the inportant lines (new and malloc)

Thanks.

[HeartBreakKid]

Originally posted by sapird

void *d_area;
int dsize=10;
d_area = malloc (dsize);
--------
char *penv = getenv ("xxxx");
char *grp;
grp = new char (sizeof (penv) + 1);

Not that this will fix your problem, but from just a quick glance I noticed that grp is not allocated correctly.....it should be:

grp = new char[sizeof(penv) + 1];

[Paul McKenzie]

Originally posted by sapird
Hi,
I try to solve a problem in a C++ code I did not write:
When I run the application I get a memory problem, and the message says that memory was allocated with new and ran over with malloc.
Is this really the problem, or is it a simptom for something else?
Is there a known problem with using new and malloc in the same application?
Another note: the problem appears only when compiled with debug information.
The application runs under OS/2 operating system.

Well, you better fix the OS/2 version if you coded this:

grp = new char (sizeof (penv) + 1);

This is incorrect. What you did here was allocate memory for a single character, and initialized it to sizeof(penv) + 1. The correct syntax is:

grp = new char [sizeof (penv) + 1];

Be lucky that the OS/2 version hasn't crashed -- yet.

Also, there is no problem with using new and malloc in the same application -- just don't mix up using malloc and delete, new with free. The rules are simple:

Allocate with malloc, deallocate with free.
Allocate with new, deallocate with delete.
Allocate with new[], deallocate with delete[].

My suggestion is to always use new or new[] for C++ programs. There is never a need to use malloc() for a C++ program. The reason why is that new calls the constructor for your object, so if your object was more complex than chars, malloc would just cause more potential problems.

Regards,

Paul McKenzie

[Bassman]

Just to add to the discussion,

grp = new char [sizeof (penv) + 1];

makes me think you really want to do:

grp = new char [strlen(penv) + 1];

since unless I'm crazy, sizeof(penv) is always 4 (a.k.a. the size of a pointer on a 32-bit system). I could be wrong, though...

Regards,
Bassman

[Paul McKenzie]

Originally posted by Bassman
Just to add to the discussion,

grp = new char [sizeof (penv) + 1];

makes me think you really want to do:

grp = new char [strlen(penv) + 1];

Yes, another bug. It should be strlen(penv) not sizeof(penv).

Regards,

Paul McKenzie

[souldog]

Not to change anything anyone has said, but MFC sometimes forces you to use malloc because that is the way they have done things for whatever reason. In particular they use it for
CMemfile, for dialog templates and for bitmap info header.

[sapird]

Thanks, guys.
The bug was in the line

grp = new char (sizeof (penv) + 1);

which was changed to

grp = new char [strlen(penv) + 1];

Who didn't I see that?

Well, thank you Paul McKenzie and Bassman of noticing the strlen/sizeof problem and thank you Paul McKenzie and HeartBreakKid for noticing the perenthesis problem.

I am very gratefull. Thanks.