I have a class for a serial-memory 2D array that was initially an array of ints. Now that I need a similar array with another type, I've rewritten the class with templates; the only difference is in the type of stored objects:
template <class T>
class Serial2DArray
{
...
T ** Content;
}
I have a few test functions that deal with Content, for example, a one that nullifies all elements in the array (they're not class members, they're outside functions working with Serial2DArray<int> objects. I've noticed that now it works 1-2% slower - all the other code in the class is untouched, the only difference is that earlier it was just a regular class with int ** Content and now it's a template.
A sort of similar question: Do c++ templates make programs slow? - has opinions that only compilation becomes slower (and I can see why, the compiler generates classes for each that it finds in the code), but here I see the program becoming slower in run-time - is there any rational explanation?
Upd: issue narrowed down a little bit here: https://stackoverflow.com/a/11058672/1200000
Upd2: as mentioned in the comments, here's the function that became slower:
#include <windows.h>
#include <mmsystem.h>
...
int Size = G_Width * G_Height * sizeof(int);
DWORD StartTime = timeGetTime();
for(int i=0; i<100; ++i)
{
FillMemory(TestArray.Content[0], Size, 0);
}
MeasuredTime = timeGetTime() - StartTime;
And here's the actual class template:
#include <malloc.h>
template <class T>
class Serial2DArray
{
public:
Serial2DArray()
{
Content = NULL;
Width = 0;
Height = 0;
}
Serial2DArray(int _Width, int _Height)
{
Initialize(_Width, _Height);
}
~Serial2DArray()
{
Deinitialize();
}
T ** Content;
int GetWidth()
{
return Width;
}
int GetHeight()
{
return Height;
}
int Initialize(int _Width, int _Height)
{
// creating pointers to the beginning of each line
if((Content = (T **)malloc(_Height * sizeof(T *))) != NULL)
{
// allocating a single memory chunk for the whole array
if((Content[0] = (T *)malloc(_Width * _Height * sizeof(T))) != NULL)
{
// setting up line pointers' values
T * LineAddress = Content[0];
for(int i=0; i<_Height; ++i)
{
Content[i] = LineAddress; // faster than Content[i] =
LineAddress += _Width; // Content[0] + i * _Width;
}
// everything went ok, setting Width and Height values now
Width = _Width;
Height = _Height;
// success
return 1;
}
else
{
// insufficient memory available
// need to delete line pointers
free(Content);
return 0;
}
}
else
{
// insufficient memory available
return 0;
}
}
int Resize(int _Width, int _Height)
{
// deallocating previous array
Deinitialize();
// initializing a new one
return Initialize(_Width, _Height);
}
int Deinitialize()
{
// deleting the actual memory chunk of the array
free(Content[0]);
// deleting pointers to each line
free(Content);
// success
return 1;
}
private:
int Width;
int Height;
};
As requested, binaries size comparison.
Code with the following:
Serial2DArray<int> TestArray;
Serial2DArray<int> ZeroArray;
- 1 016 832 bytes.
Code with the following:
Serial2DArray TestArray; // NOT-template class with ints
Serial2DArray ZeroArray; // methods are in class declaration
- 1 016 832 bytes
Code with the following:
Serial2DArray<int> TestArray;
Serial2DArray<int> ZeroArray;
Serial2DArray<double> AnotherArray;
Serial2DArray<double> YetAnotherArray;
- 1 017 344 bytes
