Clearing multidimensional STL vector

[Sascha T.]

Hi!

I didn't get the idea of exactly *how* such an array of vectors work.

Consider this minimal code:
--------------------

#include <vector>
using namespace std;

int main ()
{
vector< vector<int> > vI;
vI.resize(10);
for(int i(0); i<10; i++)
{
vI.resize(3);
}

vI.clear();
}

---------------------

Will vI.clear() really free *all* vI, too?

Or will I need another loop just before calling vI.clear() to sequentially
delete all vI: such as:

--------------
for(int i(0); i<10; i++)
{
vI.clear();
}
--------------

Thanks in advance

Yours

ST

 

[Ioannis Vranos]

Hi!

I didn't get the idea of exactly *how* such an array of vectors work.

Consider this minimal code:
--------------------

#include <vector>
using namespace std;

int main ()
{
vector< vector<int> > vI;

That is a "2-dimensional" vector.

vI.resize(10);

This makes the "rows" 10.

for(int i(0); i<10; i++)
{
vI.resize(3);
}

This makes the "columns" 3.

vI.clear();
}

It destroys all vector<int> objects contained in the vector.

Or will I need another loop just before calling vI.clear() to sequentially
delete all vI: such as:

--------------
for(int i(0); i<10; i++)
{
vI.clear();
}

No, this is not needed.


Your code in better shape:


#include <vector>

int main ()
{
using namespace std;

vector<vector<int> > vI(10, vector<int>(3));


// Not needed here
// vI.clear();
}

 

[Rolf Magnus]

Hi!

I didn't get the idea of exactly *how* such an array of vectors work.

Consider this minimal code:
--------------------

#include <vector>
using namespace std;

int main ()
{
vector< vector<int> > vI;
vI.resize(10);
for(int i(0); i<10; i++)
{
vI.resize(3);
}

vI.clear();
}

It will destroy all vI, part of which is destroying all the elements in
each of them, so the answer is yes.

Or will I need another loop just before calling vI.clear() to sequentially
delete all vI: such as:

--------------
for(int i(0); i<10; i++)
{
vI.clear();
}
--------------

No need for that.

 

[Sascha T.]

Got it, and thank you for that:

vector<vector<int> > vI(10, vector<int>(3));

Cheers

ST