How to pass smart pointer instead of "this" in C++ 11? - c++

Question

I am using c++11 compiler.
I have two classes - class Test and class TestHelper.
The class Test is a friend-to-class TestHelper.
The class Test is only which we can access from outside.
Now, we want to call Test API i.e. setVal(). This setVal() should call
Test2 API i.e. setX and is expecting this pointer. I don't want to use this pointer but want
to use a smart pointer instead. How can I do so?
The notion of this kind of desirability is because of the fact that in reality, my class Test is pretty big. So, I am trying to make a helper class for Test i.e.
class TestHelper;
class Test
{
friend class TestHelper;
int x;
public:
void display() {
std::cout << x;
}
void setVal(int val) {
TestHelper testH;
testH.setX(this, 324);
}
};
class TestHelper
{
public:
void setX(Test *test, int val) {
/** some algorithm here and then change val to something else */
test->x = val*100;
}
};
int main()
{
std::cout << "Hello World!\n";
Test x;
x.setVal(130);
}
I tried changing the prototype from void setX(Test *test, int val)
to void setX(std::shared_ptr<Test> test, int val) but don't know how to pass this pointer
as std::shared_ptr<Test> test here.

Answer 1

So here is working solution with shared pointers. The example doesn't even compile due to missing definitions so you have to restructure your code into headers and cpp files.
Test.h:
#ifndef TEST_H
#define TEST_H
#include <memory>
#include "TestHelper.h"
class Test : public std::enable_shared_from_this<Test>
{
private:
friend class TestHelper;
int x;
public:
void display();
void setVal(int val);
};
#endif
Test.cpp:
#include <iostream>
#include "Test.h"
void Test::display() {
std::cout << x;
}
void Test::setVal(int val) {
TestHelper testH;
testH.setX(shared_from_this(), 324);
}
TestHelper.h:
#ifndef TESTHELPER_H
#define TESTHELPER_H
class Test;
class TestHelper
{
public:
void setX(std::shared_ptr<Test> test, int val);
};
#endif
TestHelper.cpp:
#include <memory>
#include "TestHelper.h"
#include "Test.h"
void TestHelper::setX(std::shared_ptr<Test> test, int val) {
/** some algorithm here and then change val to something else */
test->x = val*100;
}
main.cpp:
#include <iostream>
#include <memory>
#include "Test.h"
int main(void){
std::cout << "Hello World!\n";
auto x = std::make_shared<Test>();
x->setVal(130);
x->display();
}
You can run it here: https://paiza.io/projects/e/79dehCx0RRAG4so-sVZcQw

Answer 2

I don't understand why you want this, here's a few variants that compile
reference
// Reference variant
#include <iostream>
class Test;
class TestHelper
{
public:
void setX(Test & test, int val);
};
class Test
{
friend class TestHelper;
int x;
public:
void display() {
std::cout << x;
}
void setVal(int val) {
TestHelper testH;
testH.setX(*this, 324);
}
};
void TestHelper::setX(Test &test, int val)
{
/** some algorithm here and then change val to something else */
test.x = val*100;
}
int main()
{
Test x;
x.setVal(130);
x.display();
}
http://cpp.sh/7t3ec
shared ptr
// Shared ptr variant
#include <iostream>
#include <memory> // Required for shared_ptrs
class Test;
class TestHelper
{
public:
void setX(std::shared_ptr<Test> test, int val);
};
class Test : public std::enable_shared_from_this<Test>
{
friend class TestHelper;
int x;
public:
void display() {
std::cout << x;
}
void setVal(int val) {
TestHelper testH;
testH.setX(shared_from_this(), 324);
}
};
void TestHelper::setX(std::shared_ptr<Test> test, int val)
{
/** some algorithm here and then change val to something else */
test->x = val*100;
}
int main()
{
auto x = std::make_shared<Test>(); // x needs to be created as shared_ptr or it won't work
x->setVal(130);
x->display();
}
http://cpp.sh/87ao2
Perhaps with these you can refine your question?