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returned vector of function is zeroized

The following code is a function called from the main. Sence is to
initialize a vector of the dimension of "a". "b" is the according value (all
the same in a vector).

The problem is that the initialization is done the right way (controled by
the output) but the returned vector is empty - meaning the pointer is
showing zero.

vector<int>* initialize (int a, vector<int>* vec, int b)

{

vector<int> ve;

vec=&ve;

ve.reserve(a);

for (int i=0; i<=a-1; i++)

ve[i]=b;

for (i=0; i<=a-1; i++)

cout << i << ". value : "

<< ve[i] << endl;

return vec;

ve.clear();

}

What is wrong???

I have tried it before without using a pointer - same result!
Jul 22 '05 #1
10 1621
Huibuh wrote:
The following code is a function called from the main. Sence is to
initialize a vector of the dimension of "a". "b" is the according
value (all the same in a vector).

The problem is that the initialization is done the right way
(controled by the output) but the returned vector is empty - meaning
the pointer is showing zero.

vector<int>* initialize (int a, vector<int>* vec, int b)

{

vector<int> ve;

vec=&ve;

ve.reserve(a);

for (int i=0; i<=a-1; i++)

ve[i]=b;

for (i=0; i<=a-1; i++)

cout << i << ". value : "

<< ve[i] << endl;

return vec;

ve.clear();

}

What is wrong???

I have tried it before without using a pointer - same result!


First, you're returning a address of a local. Also, I'm not sure what you're
trying to do with "vec", but I'm almost sure it isn't what you want.

What are you trying to do?

- Pete
Jul 22 '05 #2
Huibuh wrote:
The following code is a function called from the main. Sence is to
initialize a vector of the dimension of "a". "b" is the according
value (all the same in a vector).

The problem is that the initialization is done the right way
(controled by the output) but the returned vector is empty - meaning
the pointer is showing zero.

vector<int>* initialize (int a, vector<int>* vec, int b)

{

vector<int> ve;

vec=&ve;

ve.reserve(a);

for (int i=0; i<=a-1; i++)

ve[i]=b;

for (i=0; i<=a-1; i++)

cout << i << ". value : "

<< ve[i] << endl;

return vec;

ve.clear();

}

What is wrong???

I have tried it before without using a pointer - same result!


First, you're returning a address of a local. Also, I'm not sure what you're
trying to do with "vec", but I'm almost sure it isn't what you want.

What are you trying to do?

- Pete
Jul 22 '05 #3
On Mon, 5 Apr 2004 23:07:44 +0200, "Huibuh" <no*****@t-online.de> wrote:
The following code is a function called from the main. Sence is to
initialize a vector of the dimension of "a". "b" is the according value (all
the same in a vector).

The problem is that the initialization is done the right way (controled by
the output) but the returned vector is empty - meaning the pointer is
showing zero.

vector<int>* initialize (int a, vector<int>* vec, int b)

{

vector<int> ve;

vec=&ve;

ve.reserve(a);

for (int i=0; i<=a-1; i++)

ve[i]=b;

for (i=0; i<=a-1; i++)

cout << i << ". value : "

<< ve[i] << endl;

return vec;

ve.clear();

}

What is wrong???
You're creating an entire local vector in your function, setting it up, and
then it gets destroyed upon exit from the function. How about just
dispensing with the local vector and using the pointer your function is
given:

#include <iostream>
#include <vector>
using namespace std;
vector<int>* initialize (int a, vector<int>* vec, int b)

{

//vector<int> ve;

// vec=&ve;

vec->reserve(a);

for (int i=0; i<=a-1; i++)

(*vec)[i]=b;

for (i=0; i<=a-1; i++)

cout << i << ". value : "

<< (*vec)[i] << endl;

return vec;
}


int main()
{
vector<int> x;

vector<int> *vecp = initialize(10, &x, 1000);
cout << x[0] << " " << x[1] << " " << x[2] << endl;
return 0;
}

I have tried it before without using a pointer - same result!
Not sure what you mean, but not sure it matters. You /could/ have the
vector be returned by value, but that would be rather inefficient.
-leor


--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at:
www.bdsoft.com/tools/stlfilt.html
Jul 22 '05 #4
On Mon, 5 Apr 2004 23:07:44 +0200, "Huibuh" <no*****@t-online.de> wrote:
The following code is a function called from the main. Sence is to
initialize a vector of the dimension of "a". "b" is the according value (all
the same in a vector).

The problem is that the initialization is done the right way (controled by
the output) but the returned vector is empty - meaning the pointer is
showing zero.

vector<int>* initialize (int a, vector<int>* vec, int b)

{

vector<int> ve;

vec=&ve;

ve.reserve(a);

for (int i=0; i<=a-1; i++)

ve[i]=b;

for (i=0; i<=a-1; i++)

cout << i << ". value : "

<< ve[i] << endl;

return vec;

ve.clear();

}

What is wrong???
You're creating an entire local vector in your function, setting it up, and
then it gets destroyed upon exit from the function. How about just
dispensing with the local vector and using the pointer your function is
given:

#include <iostream>
#include <vector>
using namespace std;
vector<int>* initialize (int a, vector<int>* vec, int b)

{

//vector<int> ve;

// vec=&ve;

vec->reserve(a);

for (int i=0; i<=a-1; i++)

(*vec)[i]=b;

for (i=0; i<=a-1; i++)

cout << i << ". value : "

<< (*vec)[i] << endl;

return vec;
}


int main()
{
vector<int> x;

vector<int> *vecp = initialize(10, &x, 1000);
cout << x[0] << " " << x[1] << " " << x[2] << endl;
return 0;
}

I have tried it before without using a pointer - same result!
Not sure what you mean, but not sure it matters. You /could/ have the
vector be returned by value, but that would be rather inefficient.
-leor


--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at:
www.bdsoft.com/tools/stlfilt.html
Jul 22 '05 #5
Huibuh wrote:
vector<int> ve;
vec=&ve;
Ugh! Never return the address of a local variable from a function. You
should be passing the address of where you want the results (or a
reference to them) into the function for something like this or
returning the actual vector if you want a copy of it.
return vec;
ve.clear();


Do you ever expect that clear function to be called? If so, how?
Jul 22 '05 #6
Huibuh wrote:
vector<int> ve;
vec=&ve;
Ugh! Never return the address of a local variable from a function. You
should be passing the address of where you want the results (or a
reference to them) into the function for something like this or
returning the actual vector if you want a copy of it.
return vec;
ve.clear();


Do you ever expect that clear function to be called? If so, how?
Jul 22 '05 #7

"Huibuh" <no*****@t-online.de> wrote in message
news:c4*************@news.t-online.com...
The following code is a function called from the main. Sence is to
initialize a vector of the dimension of "a". "b" is the according value (all the same in a vector).

The problem is that the initialization is done the right way (controled by
the output) but the returned vector is empty - meaning the pointer is
showing zero.

vector<int>* initialize (int a, vector<int>* vec, int b)

{

vector<int> ve;

vec=&ve;

ve.reserve(a);

for (int i=0; i<=a-1; i++)

ve[i]=b;

for (i=0; i<=a-1; i++)

cout << i << ". value : "

<< ve[i] << endl;

return vec;

ve.clear();

}

What is wrong???

I have tried it before without using a pointer - same result!


Don't use a pointer, why did you think a pointer would help? They make
things more complicated not less.

Also you use reserve wrongly, reserve does NOT change the size of a vector,
so your code is putting values in a vector with zero size.

Do it like this

vector<int> initialize (int a, int b)
{
vector<int> ve(a);
for (int i=0; i<=a-1; i++)
ve[i]=b;
return ve;
}

Simple really.

john
Jul 22 '05 #8

"Huibuh" <no*****@t-online.de> wrote in message
news:c4*************@news.t-online.com...
The following code is a function called from the main. Sence is to
initialize a vector of the dimension of "a". "b" is the according value (all the same in a vector).

The problem is that the initialization is done the right way (controled by
the output) but the returned vector is empty - meaning the pointer is
showing zero.

vector<int>* initialize (int a, vector<int>* vec, int b)

{

vector<int> ve;

vec=&ve;

ve.reserve(a);

for (int i=0; i<=a-1; i++)

ve[i]=b;

for (i=0; i<=a-1; i++)

cout << i << ". value : "

<< ve[i] << endl;

return vec;

ve.clear();

}

What is wrong???

I have tried it before without using a pointer - same result!


Don't use a pointer, why did you think a pointer would help? They make
things more complicated not less.

Also you use reserve wrongly, reserve does NOT change the size of a vector,
so your code is putting values in a vector with zero size.

Do it like this

vector<int> initialize (int a, int b)
{
vector<int> ve(a);
for (int i=0; i<=a-1; i++)
ve[i]=b;
return ve;
}

Simple really.

john
Jul 22 '05 #9
Thanks to all of you, your help was very appreciated and I finally was
successful. But now I have a similar problem with RETURN correlated with a
pointer. If you are interested please see my threat

pointer return: address correct / value nonesense

Happy eastern

Jul 22 '05 #10
Thanks to all of you, your help was very appreciated and I finally was
successful. But now I have a similar problem with RETURN correlated with a
pointer. If you are interested please see my threat

pointer return: address correct / value nonesense

Happy eastern

Jul 22 '05 #11

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