Problem with references

In a function 'update()' I read and update a std::vector<MyObj> located in
another object 'Test'.

Now I would like these changes to be visible after 'update()' returns (both
for the container and the elements inside).

The function I use to read the std::vector<MyObj> therefore returns a
reference to the container:

std::vector<MyObj> & Test::getContainer()
{
return m_container;
}


Here is the implementation of 'update()'

void update(){

std::vector<MyObj> container = test.getContainer();
int size = container.size();
for (int i=0; i<size; i++) {

// Changes to objects in the container should be visible outside this
function.
MyObj & mo = container[i];
mo.setId(i);

}

// Below should be unnecessary
test->setContainer(container);


}

But the changes are not visible after 'update()' returns unless I add the
call:

test->setContainer(container);

after the above loop. But is the point of using references not that this
kind of explicit updating is unncessary?

carl

Daniel T. wrote:
> "carl" <carl@.com> wrote:
>
>> In a function 'update()' I read and update a std::vector<MyObj> located in
>> another object 'Test'.
>>
>> Now I would like these changes to be visible after 'update()' returns (both
>> for the container and the elements inside).
>>
>> The function I use to read the std::vector<MyObj> therefore returns a
>> reference to the container:
>>
>> std::vector<MyObj> & Test::getContainer()
>> {
>> return m_container;
>> }
>>
>> Here is the implementation of 'update()'
>>
>> void update(){
>>
>> std::vector<MyObj> container = test.getContainer();
>> int size = container.size();
>> for (int i=0; i<size; i++) {
>>
>> // Changes to objects in the container should be visible outside this
>> function.
>> MyObj & mo = container[i];
>> mo.setId(i);
>> }
>>
>> // Below should be unnecessary
>> test->setContainer(container);
>> }
>>
>> But the changes are not visible after 'update()' returns unless I add the
>> call:
>>
>> test->setContainer(container);
>>
>> after the above loop. But is the point of using references not that this
>> kind of explicit updating is unncessary?
>
> 'container' isn't a reference, only the return value of getContainer()
> is. Oddly, you made 'mo' a reference so you seem to understand the
> principle.
>
> Frankly, if you are going to make getContainer() return a reference
> anyway, why not just make 'm_container' public?

Or better yet make it Test::update, and have it the behavior encapsulated.

Jeff

Jeff Flinn