VECTOR problem

[Joseph]

I was doing my assignment,but encountered a problem at last step!!!!!!

for easy reading, i ommited lots of other things

//=============== ======code begin========== =============== =======
class Buyer{
void start(void);
friend void Buyer_run(Buyer *buyer);
};
void Buyer::start(vo id){
Buyer_run(this) ;
};

std::vector<Buy er> buyer_queue;

void Buyer::Buyer_ru n(Buyer* buyer){
/*============== =============== ===========
*my problem is here.how can I find out the object which stored in vector
and pointed by *buyer ?
*
*at beginning ,I did it like this,I wrote a function for Buyer class.like
*below:
*
*Buyer* Buyer::return_a ddress(void) {
*return this;
*}
*
*and then use iterator to loop the vector,after that
*I do it like this-->
*if((*iterator) .return_address ()==(*buyer).re turn_address())
*if it is true ,i will use buyer_queue.era se();to delete the element.
*
*but the if()statement never return true,why is that?????
*
*to sum up,how can I delete the element which that pointer pointed(by
only knowing/haveing that pointer)?
*============== =============== ===============
*/
};

void main{

Buyer b=Buyer();
b.start();

}

[Gernot Frisch]

"Joseph" <wu*******@hotm ail.com> schrieb im Newsbeitrag
news:Xn******** **************@ 203.96.216.21.. .

I was doing my assignment,but encountered a problem at last step!!!!!!
for easy reading, i ommited lots of other things

//=============== ======code begin========== =============== =======
class Buyer{
void start(void);
friend void Buyer_run(Buyer *buyer);
};
void Buyer::start(vo id){
Buyer_run(this) ;
};

std::vector<Buy er> buyer_queue;

void Buyer::Buyer_ru n(Buyer* buyer){
/*============== =============== ===========
*my problem is here.how can I find out the object which stored in vector and pointed by *buyer ?
*
*at beginning ,I did it like this,I wrote a function for Buyer class.like *below:
*
*Buyer* Buyer::return_a ddress(void) {
*return this;
*}
*
*and then use iterator to loop the vector,after that
*I do it like this-->
*if((*iterator) .return_address ()==(*buyer).re turn_address())
*if it is true ,i will use buyer_queue.era se();to delete the element. *
*but the if()statement never return true,why is that?????
*
*to sum up,how can I delete the element which that pointer pointed(by only knowing/haveing that pointer)?
*============== =============== ===============
*/
};

void main{

Buyer b=Buyer();
b.start();

}

Slowly, cowboy. If you allocate new objects with vector class, the
pointers to the elements might change when you add new elements or
remove some. Use a list<> if you want the pointer addresses to stay.
Next, you don't need a "return_address " function, since "&" does
exaclty this:
if (&*iterator == pointer_to_buye r) ...
If you only have the pointer to that element (why don't you have an
iterator to it!?) you would have to loop through the list (vector,
still?) and check if it's pointer addresses equal. Then you have an
iterator and can erase it. Again, adding/rmoving may change addresses
of _all_ container elements in a vector<> container! Use a list<>,
which keeps the addresses until destruction.
Best solution: Pass an iterator to that function.

HTH,

--
-Gernot
int main(int argc, char** argv) {printf
("%silto%c%cf%c gl%ssic%ccom%c" , "ma", 58, 'g', 64, "ba", 46, 10);}

_______________ _______________ __________
Looking for a good game? Do it yourself!
GLBasic - you can do
www.GLBasic.com

[Daniel T.]

Joseph <wu*******@hotm ail.com> wrote:

I was doing my assignment,but encountered a problem at last step!!!!!!

for easy reading, i ommited lots of other things

//=============== ======code begin========== =============== =======
class Buyer{
void start(void);
friend void Buyer_run(Buyer *buyer);
};
void Buyer::start(vo id){
Buyer_run(this) ;
};

std::vector<Buy er> buyer_queue;

void Buyer::Buyer_ru n(Buyer* buyer){
/*============== =============== ===========
*my problem is here.how can I find out the object which stored in vector
and pointed by *buyer ?
vector<Buyer>:: iterator it = buyer_queue.beg in();

while ( it != buyer_queue.end () || &*it != buyer ) {
++it;
}

if ( it != buyer_queue.end () ) {
// it is an iterator to the buyer in the vector
}
*but the if()statement never return true,why is that?????
Because the buyer you are passing into the function isn't in the vector.
My guess is, the problem you are having isn't in the code you posted
(which, while unconventional, should do what you want.) Your problem is
in thinking that the buyer passed into the vector is actually there.
Note your main function:
void main{ that should be 'int main() {'
Buyer b=Buyer(); the '=Buyer()' part isn't necessary.
b.start();

}

You created a Buyer object, but never added it to the vector. If you
did, I expect you did something like this:

int main() {
Buyer b;
buyer_queue.pus h_back(b);
b.start();
}

The above will not find the Buyer in the vector because 'b' isn't *in*
the vector, it's in the main function. If you do this:

int main() {
Buyer b;
buyer_queue.pus h_back(b);
buyer_queue[0].start();
}

then you will be calling start on an object that is *in* the vector.

[Howard]

"Joseph" <wu*******@hotm ail.com> wrote in message
news:Xn******** **************@ 203.96.216.21.. .

I was doing my assignment,but encountered a problem at last step!!!!!!

for easy reading, i ommited lots of other things

//=============== ======code begin========== =============== =======
class Buyer{
void start(void);
friend void Buyer_run(Buyer *buyer);
};
void Buyer::start(vo id){
Buyer_run(this) ;
};
Why use a friend function, but pass it

std::vector<Buy er> buyer_queue;

void Buyer::Buyer_ru n(Buyer* buyer){
/*============== =============== ===========
*my problem is here.how can I find out the object which stored in vector
and pointed by *buyer ?
*
*at beginning ,I did it like this,I wrote a function for Buyer class.like
*below:
*
*Buyer* Buyer::return_a ddress(void) {
*return this;
*}
*
No need for this function. A pointer itself holds the address of the
object. And for iterators you can just use &*it.
*and then use iterator to loop the vector,after that
*I do it like this-->
*if((*iterator) .return_address ()==(*buyer).re turn_address())
*if it is true ,i will use buyer_queue.era se();to delete the element.
*
*but the if()statement never return true,why is that?????
*
*to sum up,how can I delete the element which that pointer pointed(by
only knowing/haveing that pointer)?
*============== =============== ===============
*/
};

void main{

Buyer b=Buyer();
Just "Buyer b;" is all you need here. Or did you intend "Buyer* b = new
Buyer();"?
b.start();

}

I think you've removed *far* too much. You don't push b onto the vector
anywhere, so it's not in the vector. And even if you did, why immediately
search for it and remove it? Simplification for posting is fine, but not at
the expense of the meaning of the code.

Are you sure you want to store the objects themselves in the vector? You
know, a vector makes a *copy* of the object when you call push_back, so the
address of the object in the vector wil *never* be the same as the original
object. If you need to use addresses to compare objects, then you need to
push pointers, not objects. (And in that case, just compare *it with the
pointer, instead of &*it.)

-Howard

[Howard]

"Howard" <al*****@hotmai l.com> wrote in message
news:nE******** ************@bg tnsc04-news.ops.worldn et.att.net...

"Joseph" <wu*******@hotm ail.com> wrote in message
news:Xn******** **************@ 203.96.216.21.. .

I was doing my assignment,but encountered a problem at last step!!!!!!

for easy reading, i ommited lots of other things

//=============== ======code begin========== =============== =======
class Buyer{
void start(void);
friend void Buyer_run(Buyer *buyer);
};
void Buyer::start(vo id){
Buyer_run(this) ;
};

Why use a friend function, but pass it

Oops! Forgot to finish that thought! :-) Never mind...I misunderstood what
I was reading, anyway. (The lack of indentation in the post fooled me.)

-H

[JosephWu]

"Daniel T." <po********@eat hlink.net> wrote in
news:po******** *************** *******@news06. east.earthlink. net:

Joseph <wu*******@hotm ail.com> wrote:

I was doing my assignment,but encountered a problem at last
step!!!!!!

for easy reading, i ommited lots of other things

//=============== ======code begin========== =============== =======
class Buyer{
void start(void);
friend void Buyer_run(Buyer *buyer);
};
void Buyer::start(vo id){
Buyer_run(this) ;
};

std::vector<Buy er> buyer_queue;

void Buyer::Buyer_ru n(Buyer* buyer){
/*============== =============== ===========
*my problem is here.how can I find out the object which stored in
vector and pointed by *buyer ?

vector<Buyer>:: iterator it = buyer_queue.beg in();

while ( it != buyer_queue.end () || &*it != buyer ) {
++it;
}

if ( it != buyer_queue.end () ) {
// it is an iterator to the buyer in the vector
}

*but the if()statement never return true,why is that?????

Because the buyer you are passing into the function isn't in the
vector. My guess is, the problem you are having isn't in the code you
posted (which, while unconventional, should do what you want.) Your
problem is in thinking that the buyer passed into the vector is
actually there. Note your main function:

void main{

that should be 'int main() {'

Buyer b=Buyer();

the '=Buyer()' part isn't necessary.

b.start();

}

You created a Buyer object, but never added it to the vector. If you
did, I expect you did something like this:

int main() {
Buyer b;
buyer_queue.pus h_back(b);
b.start();
}

The above will not find the Buyer in the vector because 'b' isn't *in*
the vector, it's in the main function. If you do this:

int main() {
Buyer b;
buyer_queue.pus h_back(b);
buyer_queue[0].start();
}

then you will be calling start on an object that is *in* the vector.

oh,actually I did buyer_queue.pus h_back(b);

so what you mean is ,when I call .start() ,it is actually called in main
(),which its address differs from its address in the vector?

I think I should consider use list as Gernot suggested,any way,lots thank
to u 2.!!!!!!

[Daniel T.]

JosephWu <wu*******@hotm ail.com> wrote:

"Daniel T." <po********@eat hlink.net> wrote:

Joseph <wu*******@hotm ail.com> wrote:

I was doing my assignment,but encountered a problem at last
step!!!!!!

for easy reading, i ommited lots of other things

//=============== ======code begin========== =============== =======
class Buyer{
void start(void);
friend void Buyer_run(Buyer *buyer);
};
void Buyer::start(vo id){
Buyer_run(this) ;
};

std::vector<Buy er> buyer_queue;

void Buyer::Buyer_ru n(Buyer* buyer){
/*============== =============== ===========
*my problem is here.how can I find out the object which stored in
vector and pointed by *buyer ?

vector<Buyer>:: iterator it = buyer_queue.beg in();

while ( it != buyer_queue.end () || &*it != buyer ) {
++it;
}

if ( it != buyer_queue.end () ) {
// it is an iterator to the buyer in the vector
}

*but the if()statement never return true,why is that?????

Because the buyer you are passing into the function isn't in the
vector. My guess is, the problem you are having isn't in the code you
posted (which, while unconventional, should do what you want.) Your
problem is in thinking that the buyer passed into the vector is
actually there. Note your main function:

void main{

that should be 'int main() {'

Buyer b=Buyer();

the '=Buyer()' part isn't necessary.

b.start();

}

You created a Buyer object, but never added it to the vector. If you
did, I expect you did something like this:

int main() {
Buyer b;
buyer_queue.pus h_back(b);
b.start();
}

The above will not find the Buyer in the vector because 'b' isn't *in*
the vector, it's in the main function. If you do this:

int main() {
Buyer b;
buyer_queue.pus h_back(b);
buyer_queue[0].start();
}

then you will be calling start on an object that is *in* the vector.

oh,actually I did buyer_queue.pus h_back(b);

so what you mean is ,when I call .start() ,it is actually called in main
(),which its address differs from its address in the vector?

No. When you did buyer_queue.pus h_back(b) a *copy* of 'b' was placed in
the buyer_queue vector. So when you call b.start() you find that 'b'
itself is *not* in the vector (a copy is instead.)

[Howard]

>

oh,actually I did buyer_queue.pus h_back(b);

so what you mean is ,when I call .start() ,it is actually called in main
(),which its address differs from its address in the vector?

I think I should consider use list as Gernot suggested,any way,lots thank
to u 2.!!!!!!

If I'm not mistaken, list will make a copy, too, so the address is still
going to be different. But without more code, I can't tell what you're
*really* trying to do, so I can't tell if storing pointers will solve the
problem or not.

-Howard

[JosephWu]

"Howard" <al*****@hotmai l.com> wrote in
news:NI******** ************@bg tnsc05-news.ops.worldn et.att.net:

"Howard" <al*****@hotmai l.com> wrote in message
news:nE******** ************@bg tnsc04-news.ops.worldn et.att.net...

"Joseph" <wu*******@hotm ail.com> wrote in message
news:Xn******** **************@ 203.96.216.21.. .

> I was doing my assignment,but encountered a problem at last
> step!!!!!!
>
>
>
> for easy reading, i ommited lots of other things
>
> //=============== ======code begin========== =============== =======
> class Buyer{
> void start(void);
> friend void Buyer_run(Buyer *buyer);
> };
> void Buyer::start(vo id){
> Buyer_run(this) ;
> };

Why use a friend function, but pass it

Oops! Forgot to finish that thought! :-) Never mind...I
misunderstood what I was reading, anyway. (The lack of indentation in
the post fooled me.)

-H

thank u Howard,I will either use list or do like what u said: to push
pointer into vector.

[Daniel T.]

"Howard" <al*****@hotmai l.com> wrote:

oh,actually I did buyer_queue.pus h_back(b);

so what you mean is ,when I call .start() ,it is actually called in main
(),which its address differs from its address in the vector?

I think I should consider use list as Gernot suggested,any way,lots thank
to u 2.!!!!!!

If I'm not mistaken, list will make a copy, too, so the address is still
going to be different. But without more code, I can't tell what you're
*really* trying to do, so I can't tell if storing pointers will solve the
problem or not.

He's not, look at the code in his OP.