allocating array in function

[Henrietta Denoue]

Hi

I am new to C++ and suffering from dynamic allocation.
I have a function that returns an integer pointer and
want to assign this to another pointer:
class cssReader
{
public:
cssReader();
cssReader(strin g, string);
~cssReader();

public:

int* GetWandRead(str ing, int);

public:
int *d;

.....'...

}

int* cssReader::GetW andRead(string dirname, int rows)
{
.....
d = new int[duration*(int)s amprate];

// varibles duration and samprate are changing
// thats why I have to dynamically allocate my 'd'.
.....

return d;

}
using the above:
int *data;
ccReader *css = new cssReader;
void getData()
{

....
....
data = css->GetWandRead(di rname, rows);

// plot data

delete [] data;
}
first sorry for the short version of the code. It was thought
non essential.

The above sometimes works and most of the time doesn't. If I
remove the last 'delete' statement it works but having large
amount of data the memory leak is huge.
I guess my question is: Is it ok to allocate an array inside
a function, delete it outside the function and reallocate
and delete and reallocate and delete ...
Thanks in advance

H.

[modemer]

What do you mean "doesn't work"?
If you mean that the allocated memory can't be freed every time in a loop, I
guess your coding has some problem to forget free the array.

Memory (including array) could be allocated(new or malloc) in one place, and
freed in other place because it's located in heap.

"Henrietta Denoue" <he*******@netc alcul.fr> wrote in message
news:d1******** **@dolly.uninet t.no...

Hi

I am new to C++ and suffering from dynamic allocation.
I have a function that returns an integer pointer and
want to assign this to another pointer:
class cssReader
{
public:
cssReader();
cssReader(strin g, string);
~cssReader();

public:

int* GetWandRead(str ing, int);

public:
int *d;

....'...

}

int* cssReader::GetW andRead(string dirname, int rows)
{
....
d = new int[duration*(int)s amprate];

// varibles duration and samprate are changing
// thats why I have to dynamically allocate my 'd'.
....

return d;

}
using the above:
int *data;
ccReader *css = new cssReader;
void getData()
{

...
...
data = css->GetWandRead(di rname, rows);

// plot data

delete [] data;
}
first sorry for the short version of the code. It was thought
non essential.

The above sometimes works and most of the time doesn't. If I
remove the last 'delete' statement it works but having large
amount of data the memory leak is huge.
I guess my question is: Is it ok to allocate an array inside
a function, delete it outside the function and reallocate
and delete and reallocate and delete ...
Thanks in advance

H.

[Rolf Magnus]

Henrietta Denoue wrote:

Hi

I am new to C++ and suffering from dynamic allocation.
I have a function that returns an integer pointer and
want to assign this to another pointer:
class cssReader
{
public:
cssReader();
cssReader(strin g, string);
~cssReader();

public:

int* GetWandRead(str ing, int);

public:
int *d;

....'...

}

int* cssReader::GetW andRead(string dirname, int rows)
{
....
d = new int[duration*(int)s amprate];

// varibles duration and samprate are changing
// thats why I have to dynamically allocate my 'd'.
....

return d;

}
using the above:
int *data;
ccReader *css = new cssReader;
void getData()
{

...
...
data = css->GetWandRead(di rname, rows);

// plot data

delete [] data;
}
first sorry for the short version of the code. It was thought
non essential.

The above sometimes works and most of the time doesn't.
What do you mean by that? How does it not work? What does it do instead?
If I remove the last 'delete' statement it works but having large
amount of data the memory leak is huge.
I guess my question is: Is it ok to allocate an array inside
a function, delete it outside the function and reallocate
and delete and reallocate and delete ...

Yes, it is. One possible reason for problems is that you don't obey the Rule
of Three. If you need one of a copy constructor, assignment operator or
destructor, you almost certainly need all three of them. If you happen to
copy one of your cssReader objects anywhere in your program, you'll get
nasty double deletion errors.

[evaned]

The fact that d is a class member instead of a local variable to
GetWandRead raises a red flag to me... Is d used anywhere else? And if
not, does the problem go away if you make it a local variable?

I don't really see any reason why it shouldn't work to tell you the
truth. I'm not a C++ guru or anything, but I'm pretty sure that what
you have should work. So I suspect the problem is somewhere else.

[Prawit Chaivong]

Henrietta Denoue <he*******@netc alcul.fr> wrote in message news:<d1******* ***@dolly.unine tt.no>...

Hi

I am new to C++ and suffering from dynamic allocation.
I have a function that returns an integer pointer and
want to assign this to another pointer:
first sorry for the short version of the code. It was thought
non essential.

The above sometimes works and most of the time doesn't. If I
remove the last 'delete' statement it works but having large
amount of data the memory leak is huge.
I guess my question is: Is it ok to allocate an array inside
a function, delete it outside the function and reallocate
and delete and reallocate and delete ...
Thanks in advance

H.

One Question.
I just want to know whether your app is multithread apps or not?
If it is, Due to the fact that your GetData function is not thread-safe
function. It could be crashed.

Regards,

[Karl Heinz Buchegger]

Henrietta Denoue wrote:

Hi

I am new to C++ and suffering from dynamic allocation.
I have a function that returns an integer pointer and
want to assign this to another pointer:

class cssReader
{
public:
cssReader();
cssReader(strin g, string);
~cssReader();
What does the destructor do?
Does it delete[] the allocated memory?

int *data;
ccReader *css = new cssReader;
void getData()
{

...
...

data = css->GetWandRead(di rname, rows);

// plot data

delete [] data;

That's not a good idea.
You should get into the habit of:
"The object (or function) that allocated the data is
reponsible for freeing it."

That's a simple rule and there are exceptions to it, but as a rule
of thumb it works pretty well. In your example it means, since the
cssReader object allocated the memory, it is responsible for deleting
it. Not the code that created the cssReader object, not some obscure
function, nothing else but the cssReader object itself. If you keep
the code environment dealing with managing that memory small, it is much
easier to find bugs and code correctly as if some function allocates some
memory and 15000 lines of code later in some other function the deallocation
happens.

--
Karl Heinz Buchegger
kb******@gascad .at