Hi all, I wrote a class, but met some exception when I call its member
function. How to fix it? Thanks. My code is shown below:

class Myclass
{
public:
Myclass();
~Myclass();
double *showdata();

private:
double *data;
};

double *Myclass::showdata()
{
for(int i=0;i<10;i++)
data[i]=double (i);
return data;
}

My main function
#include <...>
int main()
{
Myclass *newclass = new Myclass;
newclass->showdata();//Here is the problem. what is the return value
delete newclass;
}

You just havn't allocate memory for your pointer data.

The class should be:
class MyClass
{
private:
double *data;

public:
MyClass()
{
data = NULL;
}

~MyClass()
{
if (data)
delete []data, data = NULL;
}

double *showData()
{
if (data)
delete []data;
data = new double[10];
if (!data)
return NULL;

for (int i = 0; i < 10; ++ i)
data[i] = double(i);
return data;
}
};

andylcx@hotmail.com wrote:[color=blue]
> Hi all, I wrote a class, but met some exception when I call its member
> function. How to fix it? Thanks. My code is shown below:
>
> class Myclass
> {
> public:
> Myclass();
> ~Myclass();
> double *showdata();
>
> private:
> double *data;
> };
>[/color]

You seem to have forgotten to give the definition of the ctor and the
dtor. Assuming you have a blank ctor and dtor. Lets move ahead.
[color=blue]
> double *Myclass::showdata()
> {[/color]

Memory has to be allocated for data. I would write:
data = new double[10];
[color=blue]
> for(int i=0;i<10;i++)
> data[i]=double (i);
> return data;
> }
>
> My main function
> #include <...>
> int main()
> {
> Myclass *newclass = new Myclass;
> newclass->showdata();//Here is the problem. what is the return value[/color]

The above statement causes seg fault because you forgot to allocate
memory to a pointer in showdata(). BTW, why do you need to return the
doubel array.

You could write another accessor function or use the same function to
display the values.
[color=blue]
> delete newclass;[/color]

Similar to this statement yo also need to de-allocate memory for data
by writing
delete []data;
in your showdata() function.

thanks!! and have a nice day!!
jaspreet[color=blue]
> }[/color]

ddh wrote:
[color=blue]
>
> You just havn't allocate memory for your pointer data.
>
> The class should be:
> class MyClass
> {
> private:
> double *data;
>
> public:
> MyClass()
> {
> data = NULL;
> }[/color]

Prefer initialization over assignment:

MyClass()
: data(0)
{
}
[color=blue]
> ~MyClass()
> {
> if (data)[/color]

No need for the if. Delete[] on a null pointer is a no-op anyway.
[color=blue]
> delete []data, data = NULL;
> }
>
> double *showData()
> {
> if (data)
> delete []data;
> data = new double[10];
> if (!data)
> return NULL;[/color]

No need for that check. new[] never returns a null pointer. When out of
memory, new[] throws an exception, which you actually don't handle
correctly.
[color=blue]
> for (int i = 0; i < 10; ++ i)
> data[i] = double(i);
> return data;
> }
> };[/color]

andylcx@hotmail.com wrote:[color=blue]
> Hi all, I wrote a class, but met some exception when I call its member
> function. How to fix it? Thanks. My code is shown below:
>
> class Myclass
> {
> public:
> Myclass();
> ~Myclass();
> double *showdata();
>
> private:
> double *data;
> };
>
> double *Myclass::showdata()
> {
> for(int i=0;i<10;i++)
> data[i]=double (i);
> return data;
> }
>[/color]
Where are you initialising data?

Ian