A class whose objects have variable size

[Chris Hammond]

Hi,

I am using DEV C++ 4.9.9.2 on Windows XP. I'm trying to define a matrix class, on which I can then define matrix multiplication and member functions that return its eigenvalues etc. Let me point out in advance that I realize this should probably be a template and that there are better ways of constructing a matrix class using the standard template library. However, I'm doing this for practice, so please ignore these facts for the moment.

For the moment, I just want to define a matrix class as follows:

include <cstdlib>

include <iostream>

include<cmath>

using namespace std;

class matrix {
public:
static int width;
static int height;
float MatrixArray[width][height];

} ;

int main(int argc, char *argv[])
{

system("PAUSE");
return EXIT_SUCCESS;

}

It seems like the problem is that the size of the array is not predetermined. I don't want to fix some maximum size in advance. Is there a way around this by making the member a pointer to an array?

Here is the error I get when I try to compile this.

Compiler: Default compiler
Building Makefile: "C:\Dev-Cpp\Getting Started\Matrix1\Makefile.win"
Executing make...
make.exe -f "C:\Dev-Cpp\Getting Started\Matrix1\Makefile.win" all
g++.exe -c MatrixMain1.cpp -o MatrixMain1.o -I"C:/Dev-Cpp/lib/gcc/mingw32/3.4.2/include" -I"C:/Dev-Cpp/include/c++/3.4.2/backward" -I"C:/Dev-Cpp/include/c++/3.4.2/mingw32" -I"C:/Dev-Cpp/include/c++/3.4.2" -I"C:/Dev-Cpp/include" -I"C:/Dev-Cpp/joshi"

MatrixMain1.cpp:13: error: data member may not have variably modified type `float[((unsigned int)((int)matrix::width))][((unsigned int)((int)matrix::height))]'

make.exe: *** [MatrixMain1.o] Error 1

Execution terminated

Thanks,

Chris

[Anonymous]

Ooops: I forget to init the properties and other minor mistake:

class matrix {
public:
int width; // columns
int height; // files
float** MatrixArray;

matrix (int w =0, int h =0) : width(w), height(h) {
MatrixArray = new float* [h];
for (int i = 0; i < h; i++) {
MatrixArray[i] = new float [w];
}
}

~matrix() {
for (int i = 0; i < height; i++) {
delete[] MatrixArray[i];
}
delete[] MatrixArray;
}
} ;

[Anonymous]

What about this design to Your class:

class matrix {
public:
int width;
int height;
float** MatrixArrayPtr;

matrix (int w =0, int h =0) {
    MatrixArrayPtr = new float* [h];
    for (int i = 0; i < h; i++) {
        MatrixArrayPtr[j] = new float [h];
   }
}

~matrix() {
for (int i = 0; i < height; i++) {
delete[] MatrixArrayPtr[i];
}
delete[] MatrixArrayPtr;
}
} ;