Re: questions about pointers in container
On Aug 6, 7:09 pm, "Daniel T." <danie...@earthlink.net> wrote:
trade...@yahoo.com wrote:
"Daniel T." <danie...@earthlink.net> wrote:
trade...@yahoo.com wrote:
"Daniel T." <danie...@earthlink.net> wrote:
trade...@yahoo.com wrote:
as this example,
question:
If my purpose is initialize data from xml files and store them =
in the
vector, so they can be used in class B by other member function=
s, do
you think functionP is a viable function(will a could go away a=
fter
out of the function)?
If not, is there a better solution than using functionPt?
I read that it is not a good design to have container for point=
ers(C++
FAQs), but I cannot see how I can get around it in my situation=
..
Newbie questions, thanks for the help
Chris
class A{
....
}
class B{
void functionPt(){
...
A* aPt ;
aPt has not been initialized. Copying it into a vector is technic=
ally
undefined behavior.
vPt.push_back(aPt);
}
void functionP(){
...
A a;
v.push_back(a);
}
private:
vector<A*> vPt;
vector<A> v;
}
Thanks. My fault. My intention is A* aPt = new A;
Now you have a leak.
not really. my ~B will iterate the vector and call delete.
That's not in the code you posted though... You have to add it to the
code, also what about the copy constructor and the assignment operator?
Once you take all of the above into account, and then compare the volume
of code you have to write in order to correctly implement the vector<A*>
solution, to how little you have to write to implement the vector<A>
solution, It is easy to see which is better.
Let's look at the two with all these issues covered:
class A { };
class B1 {
vector< A > vec;
public:
void func() {
vec.push_back( A() );
}
};
verses:
// I may have missed some bits, but I think this is generally corr=
ect.
class B2 {
vector< A* > vec;
public:
B2( const B2& o ) : vec( o.vec.size() ) {
try {
vector< A* >::iterator o_it = o.vec.begin();
for ( vector< A* >::iterator it = vec.begin();
it != vec.end();
++it ) {
*it = new A( *o_it );
++o_it;
}
}
catch ( ... ) {
for ( vector< A* >::iterator it = vec.begin();
it != vec.end();
++it )
delete *it;
throw;
}
}
~B2() {
for ( vector< A* >::iterator it = vec.begin();
it != vec.end();
++it )
delete *it;
}
void operator=( const B2& o ) {
B2 tmp( o );
swap( tmp.vec, vec );
}
void func() {
vec.push_back( new A );
}
};
Why would you implement B2 if you didn't absolutely have to?
Hi Daniel,
Thank you very much for your advice. I totally agree with you that it
is an awful idea to have pointers in container if I do not have to.
The codes I posted is just to illustrate a scenario so I can clarify
some fundamental concepts. I was wondering that if a local class
variable's lifetime is within the method, the object may be gone after
I go out of the method even after I put it in a member container
variable, which may force me to use pointer instead of local object in
the stack.
As clarified by Ali, I will not bother to create pointers to store
them in my vector at all.
Thanks for your time
Chris