How should be delete for this allocation

[pavan734]

Hello, I have a array of double pointers as shown below

dummy_class **ptr[10] ; //assume dummy class to be some c++ class
I have allocated it like this:

for(int i = 0 ; i<10 ; i++)
{
ptr = new dummy_class* [5] ;
for(int j=0 ; j<5 ; j++) // This 5 is because of previous
allocation of 5
{
ptr[j] = new dummy_class ;
}
}

1. Whether the above allocation is valid
2. How will be delete statements for this.

 

[S. I. Becker]

Hello, I have a array of double pointers as shown below

1. Whether the above allocation is valid
2. How will be delete statements for this.

Is this homework?

Stewart

 

[Ron Natalie]

Hello, I have a array of double pointers as shown below

dummy_class **ptr[10] ; //assume dummy class to be some c++ class
I have allocated it like this:

for(int i = 0 ; i<10 ; i++)
{
ptr = new dummy_class* [5] ;
for(int j=0 ; j<5 ; j++) // This 5 is because of previous
allocation of 5
{
ptr[j] = new dummy_class ;
}
}

1. Whether the above allocation is valid
2. How will be delete statements for this.

1, Looks OK to me.
2. The deallocation needs to mirror the allocations.

for(i = 0; i < 10; ++i) {
for(int j = 0; j < 5; ++j)
delete ptr[j];
delete ptr;
}

 

[pavan734]

1, Looks OK to me.
2. The deallocation needs to mirror the allocations.

for(i = 0; i < 10; ++i) {
for(int j = 0; j < 5; ++j)
delete ptr[j];
delete ptr;
}

Thank you. But is it not possible to delete using delete[] ?

 

[Victor Bazarov]

1, Looks OK to me.
2. The deallocation needs to mirror the allocations.

for(i = 0; i < 10; ++i) {
for(int j = 0; j < 5; ++j)
delete ptr[j];
delete ptr;
}

Thank you. But is it not possible to delete using delete[] ?

Ron made a mistake. If you allocated using 'new[]', you should
deallocate using 'delete[]'. The proper deallocation code would
be

for(int i = 0 ; i<10 ; i++) {
for(int j=0 ; j<5 ; j++)
delete ptr[j];
delete[] ptr;
}

When my OCD is acting up, I even rewrite the loops so that the
deallocations are in the reverse order of allocations:


for(int i = 10 ; i-- >0 {
for(int j=5 ; j-- >0
delete ptr[j];
delete[] ptr;
}

(I hope I got the indexing correctly :-])

V

 

[Tom Widmer]

Ron Natalie wrote:

1, Looks OK to me.
2. The deallocation needs to mirror the allocations.

for(i = 0; i < 10; ++i) {
for(int j = 0; j < 5; ++j)
delete ptr[j];
delete ptr;
}

Thank you. But is it not possible to delete using delete[] ?

Ron's code contained an error - it should be:

for(i = 0; i < 10; ++i) {
for(int j = 0; j < 5; ++j)
delete ptr[j];
delete[] ptr;
}

Every new you write should have a matching delete, and every new[] and
matching delete[].

Tom

 

[Victor Bazarov]

Hello, I have a array of double pointers as shown below

dummy_class **ptr[10] ; //assume dummy class to be some c++ class
I have allocated it like this:

for(int i = 0 ; i<10 ; i++)
{
ptr = new dummy_class* [5] ;
for(int j=0 ; j<5 ; j++) // This 5 is because of previous
allocation of 5
{
ptr[j] = new dummy_class ;
}
}

1. Whether the above allocation is valid
2. How will be delete statements for this.

1, Looks OK to me.
2. The deallocation needs to mirror the allocations.

for(i = 0; i < 10; ++i) {
for(int j = 0; j < 5; ++j)
delete ptr[j];
delete ptr;

delete[] ptr;

}

V

 

[pavan734]

Thank you everyone for your kind help.

 

[tragomaskhalos]

8 posts already in this thread and no-one has suggested that the OP use
std::vector. You guys must be going soft !

 

[Ron Natalie]

1, Looks OK to me.
2. The deallocation needs to mirror the allocations.

for(i = 0; i < 10; ++i) {
for(int j = 0; j < 5; ++j)
delete ptr[j];
delete ptr;
}

Thank you. But is it not possible to delete using delete[] ?

Actually the last one should be delete[] my mistake.