c++ templates

ashirazi · 07-28-2004, 10:10 PM

Hey guys,

Ive heard just praises about this place, but never had the opportunity to give it a shot, till today... I got this code to read a bmp file in c++, and it uses templates. Ive tried just about everything to create an object of that class, but reached nowhere. Ive compiled just the header file and it works fine, but like I said before it seems impossible to create an object of that class. The header file is as follows:

Thanks a million
ashirazi

***********************************************************

#ifndef _IMAGE_CLASS
#define _IMAGE_CLASS

#include<string.h> // for memcpy();
#include<assert.h> // for assert();
#include<fstream.h>

const int STRING_SIZE = 512;
typedef char String[STRING_SIZE + 1];
//end sudeep

template <class T> class Image
{
public:
// constructor and destructor
Image();
Image( int nRows, int nCols);
Image( Image& m);
~Image();

// operations
void Initialize( T x=0);
int ResetSize(int rows, int cols);

// operator overload
operator T** (){ return m_ptr; }
void operator=(const Image& m);

// data access
T** GetBuffer(){ return m_ptr; }
int Rows(){ return m_nRows; }
int Cols(){ return m_nCols; }

T& CellAt(int col, int row); // safe access

int Read( const char* fn); //read from fn according to m_nRows & m_nCols
int Write( const char* fn);

protected:
void FreeMem();

private:
T** m_ptr; // the 3-D pointer.
int m_nRows;
int m_nCols;

};

#endif

***********************************************************

#include"image.h"
// implementation

// constructors and destructor
template <class T>
Image<T>::Image():m_nRows(0),m_nCols(0),m_ptr(NULL)
{
}

template <class T>
Image<T>::Image(int rows, int cols):m_nRows(rows),m_nCols(cols)
{
m_ptr=NULL;
int bSuc=ResetSize(rows, cols);
}

template <class T>
Image<T>::Image(Image& m): m_nRows(m.m_nRows),m_nCols(m.m_nCols),m_ptr(NULL)
{
int bSuc=ResetSize(m_nRows,m_nCols);

m_ptr = new T*[m_nRows];
assert(m_ptr != NULL);
for(int row=0; row<m_nRows; row++)
{
m_ptr[row] = new T[m_nCols];
assert(m_ptr[row]!= NULL);
}

for(int r=0; r<m_nRows; r++)
for(int c=0; c<m_nCols; c++)
m_ptr[r][c] = m.m_ptr[r][c];
}

template <class T>
Image<T>::~Image()
{
FreeMem();
}

template <class T>
void Image<T>::FreeMem()
{
int i;
if( m_ptr != NULL)
{
for(i=0;i<m_nRows;i++)
{
if( m_ptr[i] != NULL )
{
delete []m_ptr[i]; // delete the datablock
m_ptr[i] = NULL;
}
}
delete []m_ptr; // Delete the row pointers
m_ptr = NULL;
}
}

template <class T>
void Image<T>::Initialize(T x)
{
for(int r=0; r<m_nRows; r++)
for(int c=0; c<m_nCols; c++)
m_ptr[r][c] = x;
}

template <class T>
int Image<T>::ResetSize(int rows, int cols)
{
assert(rows>0 && cols>0); // make sure the dimensions are legal

FreeMem(); // Deallocate if neccessary

m_nRows = rows;
m_nCols = cols;

m_ptr = new T*[m_nRows];
assert(m_ptr != NULL);
for(int row=0; row<m_nRows; row++)
{
m_ptr[row] = new T[m_nCols];
assert(m_ptr[row]!= NULL);
}

return 1;
}

template <class T>
void Image<T>:

perator=(const Image& rhs)
{
if(this != &rhs)
{
ResetSize(rhs.m_nRows, rhs.m_nCols);
for(int r=0; r<m_nRows; r++)
for(int c=0; c<m_nCols; c++)
m_ptr[r][c] = rhs.m_ptr[r][c];
}
return *this;
}

template <class T>
T& Image<T>::CellAt( int row, int col)
{
assert((0<= row) &&(row<m_nRows));
assert((0<= col) &&(col<m_nCols));
return m_ptr[row][col];
}

template <class T>
int Image<T>::Read( const char* fn)
{
ifstream ins;
ins.open(fn);
if(ins.bad() )
{
cerr<<"Input file:"<<"["<<fn<<"]"<<" open failed!"<<endl;
return 0;
}
cout << "file opened to read" << endl;
long size = m_nRows * m_nCols * sizeof(T);
int i,j;
for(i=0; i < m_nRows; i++)
{
for(j=0; j < m_nCols; j++)
ins.read((char*)&m_ptr[i][j], sizeof(T));
}
ins.close();
return size;
}

template <class T>
int Image<T>::Write( const char* fn)
{
ofstream outs;
outs.open(fn);
if(outs.bad())
{
cerr<<"Output file:"<<"["<<fn<<"]"<<" open failed!"<<endl;
return 0;
}

long size = m_nRows * m_nCols * sizeof(T);

int i,j;
for(i=0; i < m_nRows; i++)
{
for(j=0; j < m_nCols; j++)
outs.write((char*)&m_ptr[i][j], sizeof(T));
}
outs.close();
return size;
}

Hano · 07-29-2004, 12:04 AM

oh! i thought g++ didnt supported well implementation of template members outside the declaration header file. what version of g++ are u using?

ashirazi · 07-29-2004, 02:03 AM

Im using borland c++, for windows XP.

dakensta · 07-29-2004, 05:34 AM

Following on from Hano's point, read this FAQ and the one after it:

http://www.parashift.com/c++-faq-lit...html#faq-34.12

ashirazi · 07-29-2004, 08:01 PM

Dakensta,

i read through the whole thing but it really didnt help much, as i still couldnt make an object of class. I basically knew most of what the FAQ was talking about but still couldnt apply it in this case. Can you please give it a shot?

Thans
Shirazi

dakensta · 07-30-2004, 05:17 AM

I guess from your code that the files are in a .h header and a .cpp implementation.

I copied all the source into one header file and wrote an implementation instantiating an image,

Code:

#include <iostream>

#include "bmptmp.hpp"  // copied your source above into this file

int main()
{
  Image<char> I(100, 100);
  Image<char> J();
  Image<char> K(I);
}

and it compiled (albeit with some warnings

). I am using g++ 3.3.x, if there any borland specific issues, I am afraid I am unable to comment.

My advice is either to put the declaration and defintion in one file, "image.h", or use the technique mentioned of putting #include "template_definition.cpp" at the bottom of the header file.

HTH