C++ Challenge - Local Reference

C++ Challenge - Local Reference - Printable Version

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C++ Challenge - Local Reference - ArkPhaze - 06-29-2014

Code:
#include <iostream>

std::string get_string()
{
  return std::string("My String");
}

int main()
{
  /* declare 'obj' as a reference to the temporary 
  string object returned by get_string() below... 
  (remember: references use &, i.e. std::string &var_name, for instance)*/

  // -- CODE HERE --

  std::cout << "Before: " << obj << std::endl;
  obj = "Changed!";
  std::cout << "Modified: " << obj << std::endl;
}

Description is commented within the above code. You can't change any of the existing code, you can only add code where specified (// -- CODE HERE -- ). You must create a std: Confused

tring object which is a reference to the local variable returned by the get_string() function, and the code must compile, containing all of the existing code. You can't modify the function get_string() at all either. Smile

NOTE: Because of the context of the given code, this is a C++11 challenge...

Good luck.

RE: C++ Challenge - Local Reference - ArkPhaze - 06-29-2014

Those of you who think C++ is nice and straightforward, I'll guarantee that this one will rack your brain. Wink

edit: I see how this is going to go... Boring.

RE: C++ Challenge - Local Reference - lady_godiva - 07-08-2014

Here's the solution:

Code:
#include <iostream>

std::string get_string()
{
  return std::string("My String");
}

int main()
{
  /* declare 'obj' as a reference to the temporary
  string object returned by get_string() below...
  (remember: references use &, i.e. std::string &var_name, for instance)*/

  // -- CODE HERE --
  
  std::string&& obj = const_cast<std::string&&>(get_string());

  std::cout << "Before: " << obj << std::endl;
  obj = "Changed!";
  std::cout << "Modified: " << obj << std::endl;
}

Nice one!

RE: C++ Challenge - Local Reference - ArkPhaze - 07-18-2014

Or..

Code:
std::string&& obj = std::move(get_string());

Example:

Code:
#include <iostream>

class MyClass
{
public:
  MyClass() : x_(0) {}
  MyClass(int x) : x_(x) {}
  const int &get_x() const { return x_; }
  void set_x(int x) { x_ = x; }
private:
  int x_;
};

MyClass f(int x) { return MyClass(x); }

int main()
{
  using namespace std;
  MyClass obj1 = f(1);
  cout << "Object 1 constructed with x = " << obj1.get_x() << endl;
  MyClass &&obj2 = std::move(obj1);
  cout << "Object 2 created from an rvalue reference to Object 1" << endl;

  int value = 99;
  cout << "Setting Object 2's x value to " << value << endl;
  obj2.set_x(value);
  std::cout << "Object 1's x value is " << obj1.get_x() << std::endl;
}

RE: C++ Challenge - Local Reference - lady_godiva - 07-18-2014

You are right but when i made this i thought i was only allowed to use the obj variable

RE: C++ Challenge - Local Reference - ArkPhaze - 07-20-2014

(07-18-2014, 07:20 AM)lady_godiva Wrote: You are right but when i made this i thought i was only allowed to use the obj variable

My solution is only using the obj variable too...? :S

RE: C++ Challenge - Local Reference - lady_godiva - 07-20-2014

(07-20-2014, 08:49 PM)ArkPhaze Wrote:
(07-18-2014, 07:20 AM)lady_godiva Wrote: You are right but when i made this i thought i was only allowed to use the obj variable

My solution is only using the obj variable too...? :S

In your code you use both obj1, obj2 and you defined your own class. What i meant is that i was thinking i had too use a single line of code to solve it Wink

RE: C++ Challenge - Local Reference - ArkPhaze - 07-21-2014

(07-20-2014, 09:28 PM)lady_godiva Wrote:
(07-20-2014, 08:49 PM)ArkPhaze Wrote:
(07-18-2014, 07:20 AM)lady_godiva Wrote: You are right but when i made this i thought i was only allowed to use the obj variable

My solution is only using the obj variable too...? :S

In your code you use both obj1, obj2 and you defined your own class. What i meant is that i was thinking i had too use a single line of code to solve it

That was an added example of std::move().... I think you are confused here. This is one line:

Code:
std::string&& obj = std::move(get_string());

Is it not?

That example code isn't even the same as the challenge code. I provided that for demonstration only...

RE: C++ Challenge - Local Reference - lady_godiva - 07-21-2014

(07-21-2014, 05:50 AM)ArkPhaze Wrote:
(07-20-2014, 09:28 PM)lady_godiva Wrote:
(07-20-2014, 08:49 PM)ArkPhaze Wrote:
(07-18-2014, 07:20 AM)lady_godiva Wrote: You are right but when i made this i thought i was only allowed to use the obj variable

My solution is only using the obj variable too...? :S

In your code you use both obj1, obj2 and you defined your own class. What i meant is that i was thinking i had too use a single line of code to solve it

That was an added example of std::move().... I think you are confused here. This is one line:

Code:
std::string&& obj = std::move(get_string());

Is it not?

That example code isn't even the same as the challenge code. I provided that for demonstration only...

oooo my bad hahaha, forgive me, i didn't see that single line in your post when you replied me!