ptr to member

[trying_to_learn]

im trying to index through an array that is member of a class using ptr
to member

in main i tried making a ptr to the member 'arr' :

const int * testclass7::* ptrToMemberIntP tr = &testclass7::ar r;
------------------------------------------------------
the compiler cries:
cannot convert from 'int (testclass7::*)[10]' to 'const int *testclass7::* '
Types pointed to are unrelated; conversion requires reinterpret_cas t,
C-style cast or function-style cast
------------------------------------------------------
I cant figure this out... isnt arr basically a const int * ?
how do i define a ptr to member arr?

class testclass7
{
public:
int arr[10];
testclass7(int arg=1)
{
for (int i=0;i<sizeof(ar r) / sizeof(*arr);i+ +)
{
arr[i] = arg+i;
}
}
};

[Alf P. Steinbach]

* trying_to_learn :

im trying to index through an array that is member of a class using ptr
to member
Instead provide a []-operator.

Pointer to member is very seldom necessary, and pointer to data member
is absolutely EVIL.

Don't use it.

in main i tried making a ptr to the member 'arr' :

const int * testclass7::* ptrToMemberIntP tr = &testclass7::ar r;
------------------------------------------------------
the compiler cries:
cannot convert from 'int (testclass7::*)[10]' to 'const int *testclass7::* '
Types pointed to are unrelated; conversion requires reinterpret_cas t,
C-style cast or function-style cast
------------------------------------------------------
I cant figure this out... isnt arr basically a const int * ?
No, it's not const, and it's not a pointer: it's an array.

how do i define a ptr to member arr?

class testclass7
{
public:
int arr[10];
testclass7(int arg=1)
{
for (int i=0;i<sizeof(ar r) / sizeof(*arr);i+ +)
{
arr[i] = arg+i;
}
}
};

Like this:

int main()
{
testclass7 obj;
int (testclass7::* p)[10] = &testclass7::ar r;

for( int i = 0; i < 10; ++i )
{
std::cout << (obj.*p)[i] << std::endl;
}
}

But don't use it.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Rolf Magnus]

trying_to_learn wrote:

im trying to index through an array that is member of a class using ptr
to member

in main i tried making a ptr to the member 'arr' :

const int * testclass7::* ptrToMemberIntP tr = &testclass7::ar r;
------------------------------------------------------
the compiler cries:
cannot convert from 'int (testclass7::*)[10]' to 'const int *testclass7::*
' Types pointed to are unrelated; conversion requires reinterpret_cas t,
C-style cast or function-style cast
Uh... a compiler suggesting a reinterpret_cas t and a C style cast... evil.
------------------------------------------------------
I cant figure this out... isnt arr basically a const int * ?
No. arr is an array of 10 ints. Look at the error message. What you'd need
is a member pointer to an array of int, not a member pointer to a pointer.
Anyway, why do you think you need a member pointer at all?
how do i define a ptr to member arr?
Uhm, look at the error message. It tells you.
class testclass7
{
public:
int arr[10];
testclass7(int arg=1)
{
for (int i=0;i<sizeof(ar r) / sizeof(*arr);i+ +)
{
arr[i] = arg+i;
}
}
};