Question

Is it possible to dynamically allocate a temporary variable in C++ ?

I want to do something like that :

#include <iostream>
#include <string>

std::string* foo()
{
  std::string ret("foo");
  return new std::string(ret);
}

int main()
{
  std::string *str = foo();
  std::cout << *str << std::endl;                                                                                                           
  return 0;
}

This code works but the problem is I have to create an other string in order to return it as a pointer. Is there a way to put my temporary/local variable inside my heap without recreate an other object ?

Here is an illustration of how I would do that :

std::string* foo()
{
  std::string ret("foo");
  return new ret; // This code doesn't work, it is just an illustration
}

Answer 1

Well yes there is, it’s called smart pointers:

#include <memory>
std::unique_ptr<std::string> foo()
{
    return std::unique_ptr<std::string>("foo");
}

// Use like this:
using namespace std;
auto s = foo();     // unique_ptr<string> instead of auto if you have an old standard.
cout << *s << endl; // the content pointed to by 's' will be destroyed automatically
                    // when you stop using it

Edit: without changing the return type:

std::string* foo()
{
    auto s = std::unique_ptr<std::string>("foo");
    // do a lot of stuff that may throw

    return s.release(); // decorellate the string object and the smart pointer, return a pointer
                        // to the string
}