Pass pointer by reference c++

Question

Yes I have read a lot of tutorials and questions and also tried a lot of combinations but it seems not to work. My goal is not to use dynamic allocation.

My classes look like this:

Pages
Page
PMain:Page
PCam:Page

on my main when I do this:

1. main:

Page * page;
PCam main;
main.setContext(context);
page = &main;
page->echo();

result: PCam

but when I try to create the instance inside an outside class and point it to page it fails.

2.

pages class:

Pages::Pages(Page*& page, Context& context){
    this->context = &context;
    PMain main;
    main.setContext(*this->context);
    main.echo();
    // page = &main; <---
} 

main:

Page * page;
Pages pages(page, context);
page->echo();

result: Page

expected result: PCam

My classes:

Page:

void Page::setContext(Context & context)
{
    this->context = &context;
}
void Page::echo()  //virtual
{
    std::cout << "echo Page"  << std::endl;
}

PMain:

void PMain::echo(){
    std::cout << "echo PMain"  << std::endl;}
}

PCam:

void PCam::echo(){
    std::cout << "echo PCam"  << std::endl;}
}

Any help would be appreciated. thanks.

Answer 1

Your problem, or one of them, is that this:

Pages::Pages(Page*& page, Context& context){
    [...]
    PMain main;

is a local stack variable. When this function returns, it ceases to exist. If you've assigned it to a pointer, you'll get undefined behavior by using it.

My goal is not to use dynamic allocation.

Unless you have some specific reason, this is a mostly pointless goal. If you want a pointer to a stack object (i.e., one that's not dynamically allocated), that object must remain in scope as long as you use the pointer. If you can't do that, then you need to put it on the heap (i.e., dynamically allocate).