Scope of std::vector

[Steve]

I have defined the following private object:

std::vector<Ban ana> bananas;

in my header file. I have also added a method called FillVector(), which
sets the size of the vector and fills it with Banana objects.

In another method (getSecondBanan a()) I want to access the contents of
bananas, using e.g.

Banana second_banana;
second_banana = bananas[1];

Unfortunately my program crashes when I try to do it like this. However it
*does* work when I fill the vector in the same method as I try to access the
contents of this. This suggests to me that the scope of the vector is
restricted to the method it is filled in. How do I set the scope of such an
object so that it can be accessed from anywhere within the class?

[Jacques Labuschagne]

Steve wrote:

Unfortunately my program crashes when I try to do it like this. However it
*does* work when I fill the vector in the same method as I try to access the
contents of this. This suggests to me that the scope of the vector is
restricted to the method it is filled in. How do I set the scope of such an
object so that it can be accessed from anywhere within the class?

There's nothing wrong with this as long as you FillVector before you
getSecondBanana . Post the code and we'll help you out further.

Jacques.

[Sumit Rajan]

"Steve" <st***@hello.co m> wrote in message news:43******** **@x-privat.org...

I have defined the following private object:

std::vector<Ban ana> bananas;

in my header file. I have also added a method called FillVector(), which
sets the size of the vector and fills it with Banana objects.

In another method (getSecondBanan a()) I want to access the contents of
bananas, using e.g.

Banana second_banana;
second_banana = bananas[1];

Unfortunately my program crashes when I try to do it like this. However it
*does* work when I fill the vector in the same method as I try to access
the contents of this. This suggests to me that the scope of the vector is
restricted to the method it is filled in. How do I set the scope of such
an object so that it can be accessed from anywhere within the class?

Could you please post some code that demonstates your problem? Please
remember to keep it minimal and compile-able:
http://www.parashift.com/c++-faq-lit...t.html#faq-5.8
Regards,
Sumit.
--
Sumit Rajan <su*********@gm ail.com>

[Sumit Rajan]

"Steve" <st***@hello.co m> wrote in message news:43******** **@x-privat.org...

I have defined the following private object:

std::vector<Ban ana> bananas;

in my header file. I have also added a method called FillVector(), which
sets the size of the vector and fills it with Banana objects.

In another method (getSecondBanan a()) I want to access the contents of
bananas, using e.g.

Banana second_banana;
second_banana = bananas[1];

Unfortunately my program crashes when I try to do it like this. However it
*does* work when I fill the vector in the same method as I try to access
the contents of this. This suggests to me that the scope of the vector is
restricted to the method it is filled in. How do I set the scope of such
an object so that it can be accessed from anywhere within the class?

Could you please post some code that demonstates your problem? Please
remember to keep it minimal and compile-able:
http://www.parashift.com/c++-faq-lit...t.html#faq-5.8
Regards,
Sumit.
--
Sumit Rajan <su*********@gm ail.com>

[Karl Heinz Buchegger]

Steve wrote:

I have defined the following private object:

std::vector<Ban ana> bananas;

in my header file. I have also added a method called FillVector(), which
sets the size of the vector and fills it with Banana objects.

In another method (getSecondBanan a()) I want to access the contents of
bananas, using e.g.

Banana second_banana;
second_banana = bananas[1];

Unfortunately my program crashes when I try to do it like this. However it
*does* work when I fill the vector in the same method as I try to access the
contents of this. This suggests to me that the scope of the vector is
restricted to the method it is filled in. How do I set the scope of such an
object so that it can be accessed from anywhere within the class?

Your analysis is wrong.
The only thing I can conclude from what you wrote, is:
You may have passed the vector the wrong way: pass per
value instead of pass per reference.

An analogy. In ...

void foo( int i )
{
i = 5;
}

int main()
{
int j = 3;
foo( j );
/// <- Here j still has the value 3, since a copy of j is
/// passed *per value* to foo.
}

.... why does j still have the value 3, when foo attempted to change it
to 5. The answer is: because j is passed per value, a copy of it is passed
to foo. You can change that copy inside foo as often as you like in foo,
that will not impress j.

On the other hand:

void foo( int& i )
{
i = 5;
}
int main()
{
int j = 3;
foo( j );
/// <- Here j has the new value of 5, since it is passed per reference to foo.
/// foo creates a new name for j, inside foo j is known as i. Whatever happens
/// to i, happens to j, since j and i are the same variable.
}

If this is not what you did wrong, then post your code.

--
Karl Heinz Buchegger
kb******@gascad .at

[Steve]

"Sumit Rajan" <su*********@gm ail.com> wrote in message
news:3r******** ****@individual .net...

Could you please post some code that demonstates your problem? Please
remember to keep it minimal and compile-able:
http://www.parashift.com/c++-faq-lit...t.html#faq-5.8

OK, I'll post the code when I get home (I don't have access to it here).

[Greg]

Karl Heinz Buchegger wrote:

Steve wrote:

I have defined the following private object:

std::vector<Ban ana> bananas;

in my header file. I have also added a method called FillVector(), which
sets the size of the vector and fills it with Banana objects.

In another method (getSecondBanan a()) I want to access the contents of
bananas, using e.g.

Banana second_banana;
second_banana = bananas[1];

Unfortunately my program crashes when I try to do it like this. However it
*does* work when I fill the vector in the same method as I try to access the
contents of this. This suggests to me that the scope of the vector is
restricted to the method it is filled in. How do I set the scope of such an
object so that it can be accessed from anywhere within the class?

Your analysis is wrong.
The only thing I can conclude from what you wrote, is:
You may have passed the vector the wrong way: pass per
value instead of pass per reference.

....

Well it is also possible that there are simply two different vectors
both named bananas. As usual, having the source would probably help
shed more light on the matter.

Also, could we have a ruling on the legality of "Banana" and "bananas"
as legal C++ identifiers? Based on my knowledge acquired from this
newsgroup, I believe that the only legally recognized identifiers
permitted in a well-formed C++ program are "foo" and "bar".

Greg

[Ali Çehreli]

"Steve" <st***@hello.co m> wrote in message news:43******** **@x-privat.org...

I have defined the following private object:

std::vector<Ban ana> bananas;

in my header file. I have also added a method called FillVector(), which
sets the size of the vector and fills it with Banana objects.
You don't show how you're filling the vector. One sure way is

bananas.push_ba ck(my_banana);
bananas.push_ba ck(your_banana) ;
// etc.
In another method (getSecondBanan a()) I want to access the contents of
bananas, using e.g.

Banana second_banana;
second_banana = bananas[1];
You are not accessing the contents of bananas. You are taking a copy of the
second element.
Unfortunately my program crashes when I try to do it like this. However it
*does* work when I fill the vector in the same method as I try to access
the contents of this.
We can only guess: Does Banana need and provide copy constructor, operator=,
and destructor?
This suggests to me that the scope of the vector is restricted to the
method it is filled in.
You don't show but I think bananas is a member of a class. In that case,
bananas will be alive as long as the encapsulating object is alive.
How do I set the scope of such an object so that it can be accessed from
anywhere within the class?

It already happens. You have a bug somewhere else.

Ali

[BobR]

Greg wrote in message
<11************ *********@g47g2 000cwa.googlegr oups.com>...

Also, could we have a ruling on the legality of "Banana" and "bananas"
as legal C++ identifiers? Based on my knowledge acquired from this
newsgroup, I believe that the only legally recognized identifiers
permitted in a well-formed C++ program are "foo" and "bar".
Greg

You are trying to compare apples to oranges!
[ you also forgot 'widgets'. ]

--
Bob '<G>' R
POVrookie

[Steve]

"Sumit Rajan" <su*********@gm ail.com> wrote in message
news:3r******** ****@individual .net...

Could you please post some code that demonstates your problem? Please
remember to keep it minimal and compile-able:
http://www.parashift.com/c++-faq-lit...t.html#faq-5.8

I get error Unhandled exception at 0x00415329 in ClientTestClass es.exe:
0xC0000005: Access violation reading location 0x000002c4. It's something to
do with the way I'm filling and/or accessing the vector.

I need to get RequestCall() to return a call from the call_list vector.

/* Manager.cpp */

void Manager::Login( )
{
proxy.FillVecto rs(); /* fills the vector in ClientProxy */
proxy.RequestCa ll(current_camp aign); /* crash occurs in this method */
}

/* ClientProxy.h */
#ifndef __CLIENTPROXY__
#define __CLIENTPROXY__
#include "Call.h"
#include "Campaign.h "
#include "User.h"
#include "vector"
using namespace std;
class ClientProxy

{

public:
ClientProxy();
User Login(const std::string& sname, const std::string& ip, int pn);
Campaign RequestCampaign s(User u);
Call RequestCall(Cam paign c);
bool MarshallRequest ();

void FillVectors();

private:
/* Test variables below */
Call GetNextCall();
int call_counter;

/* Real vars */
Call current_call;
Campaign current_campaig n;
User user;
vector<Campaign > campaigns;
vector<Call> call_list;
};
/* END CLASS DEFINITION ClientProxy */

#endif

/* ClientProxy.cpp */

#include "ClientProx y.h"
#include "Call.h"
#include <vector>

ClientProxy::Cl ientProxy()
{

}

void ClientProxy::Fi llVectors()
{
printf("\n-FillVectors()") ;
vector<Campaign > campaigns(5);
campaigns[0] = Campaign(1, "Camp1");
campaigns[1] = Campaign(2, "Camp2");
campaigns[2] = Campaign(3, "Camp3");
campaigns[3] = Campaign(4, "Camp4");
campaigns[4] = Campaign(5, "Camp5");

vector<Call> call_list(5);
call_list[0] = Call(1,"0121575 5533","","Dave Jones","Jones
Construction"," 123 Main Street","",""," ");
call_list[1] = Call(2,"0121573 1432","","Steve Martin","Martin s
Butchers","10 West Street","",""," ");
call_list[2] = Call(3,"0131543 5467","","Phil Babb","BB Insurance","3 North
Street","",""," ");
call_list[3] = Call(4,"0141577 2234","","Tony Van Bronkel","GVK", "12 South
Street","",""," ");
call_list[4] = Call(5,"0151812 6534","","Steve Alabaster","MRM ","13 High
Street","",""," ");
call_counter = 0;

//printf(call_lis t[0].GetName().c_st r());
}

User ClientProxy::Lo gin(const std::string& sname, const std::string& ip, int
pn)
{
user.SetName(sn ame);
user.SetUserID( 1);
//call_list.inser t(sname);
return user;
}

Campaign ClientProxy::Re questCampaigns( User u)
{
return current_campaig n;
}

Call ClientProxy::Re questCall(Campa ign c)
{
//current_call = GetNextCall();

current_call = call_list[3]; /* ERROR BREAKS HERE */
printf("\n");
printf("-ClientProxy.Req uestCall()");
printf(current_ call.GetName(). c_str());
printf("-eof");
return current_call;
}

/* This is a temporary method to retrieve the contents of the call_list
vector */
Call ClientProxy::Ge tNextCall() {
Call ctemp = call_list[call_counter];
call_counter++;
return ctemp;
}

bool ClientProxy::Ma rshallRequest()
{
return 1;
}