Can I simulate move constructor & move assignment operator functionality with copy constructor and assignment operator in C++98 to improve the performance whenever i know copy constructor & copy assignment will be called only for temporary object in the code OR i am inserting needle in my eyes?
I have taken two example's one is normal copy constructor & copy assignment operator and other one simulating move constructor & move assignment operator and pushing 10000 elements in the vector to call copy constructor.
Example(copy.cpp) of normal copy constructor & copy assignment operator
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
class MemoryBlock
{
public:
// Simple constructor that initializes the resource.
explicit MemoryBlock(int length)
: _length(length)
, _data(new int[length])
{
}
// Destructor.
~MemoryBlock()
{
if (_data != NULL)
{
// Delete the resource.
delete[] _data;
}
}
//copy constructor.
MemoryBlock(const MemoryBlock& other): _length(other._length)
, _data(new int[other._length])
{
std::copy(other._data, other._data + _length, _data);
}
// copy assignment operator.
MemoryBlock& operator=(MemoryBlock& other)
{
//implementation of copy assignment
}
private:
int _length; // The length of the resource.
int* _data; // The resource.
};
int main()
{
// Create a vector object and add a few elements to it.
vector<MemoryBlock> v;
for(int i=0; i<10000;i++)
v.push_back(MemoryBlock(i));
// Insert a new element into the second position of the vector.
}
Example(move.cpp) of simulated move constructor & move assignment operator functionality with copy constructor & copy assignment operator
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
class MemoryBlock
{
public:
// Simple constructor that initializes the resource.
explicit MemoryBlock(int length=0)
: _length(length)
, _data(new int[length])
{
}
// Destructor.
~MemoryBlock()
{
if (_data != NULL)
{
// Delete the resource.
delete[] _data;
}
}
// Move constructor.
MemoryBlock(const MemoryBlock& other)
{
// Copy the data pointer and its length from the
// source object.
_data = other._data;
_length = other._length;
// Release the data pointer from the source object so that
// the destructor does not free the memory multiple times.
(const_cast<MemoryBlock&>(other))._data = NULL;
//other._data=NULL;
}
// Move assignment operator.
MemoryBlock& operator=(const MemoryBlock& other)
{
//Implementation of move constructor
return *this;
}
private:
int _length; // The length of the resource.
int* _data; // The resource.
};
int main()
{
// Create a vector object and add a few elements to it.
vector<MemoryBlock> v;
for(int i=0; i<10000;i++)
v.push_back(MemoryBlock(i));
// Insert a new element into the second position of the vector.
}
I observed performance is improved with some cost:
$ g++ copy.cpp -o copy
$ time ./copy
real 0m0.155s
user 0m0.069s
sys 0m0.085s
$ g++ move.cpp -o move
$ time ./move
real 0m0.023s
user 0m0.013s
sys 0m0.009s
We can observe that performance is increased with some cost.
- Has any pitfall to implement move constructor and move assignment operator simulated functionality in c++98, even I am sure that copy constructor & assignment only call when temporary objects are created?
- Has there any other way/technique to implement the move constructor and assignment operator in c++98?
std::auto_ptrhas something similar to move semantics, and that involves dealing with a constructor taking a non-const reference to the object. – Andre Kostur