Embedded Systems Design - June 2008 - (Page 15)

Listing 1 Some constructors. // default constructor; creates a matrix of default dimensions Matrix::Matrix() { assert(matClassRows >0); assert(matClassCols >0); m = matClassRows; n = matClassCols; p = new double[m*n]; vClear(p, m*n); } // Copy constructor Matrix::Matrix(const Matrix &a) { m = a.m; n = a.n; p = new double[m*n]; vCopy(a.p, p, m*n); } The default constructor and the copy constructor are shown in Listing 1. Note the use of the low-level functions vClear and vCopy, from the ﬁle SimpleVec.cpp. More about these functions later. The use of vClear is demanded by the charter of SEUV. ARRAY TO MATRIX Perhaps the most important and useful constructor is the third one, which builds a new vector, copying its data from an ordinary C array. Why is it so important? Because it’s one of the few ways, short of reading an input ﬁle, that we can stuff data into the matrix elements. It’s the closest we’re likely to come to an initializer for objects of this class. The constructor, shown in Listing 2, borrows heavily from its cousin in class Vector. The difference is that, in the earlier constructor, the transfer of data is a simple element-by-element copy from one singly dimensioned array to another. In the new constructor, the transfer of data is a little more subtle. It also goes back to that issue of how array data are stored in memory, which I discussed in my last column. As before, it’s worth taking the time to discuss the details. As we do so, we’ll discover one last “gotcha” that the C syntax has in store for us. Look carefully at the declaration of the constructor. The input array is declared to be double a[ ], that is, an ordinary single-dimensioned array of doubles. To initialize that array, I might write: double a[9] = {1, 2, 3, 4, 5, 6, 7, 8, 9}; Listing 2 The converting constructor. // Converting constructor from array Matrix::Matrix(double a[], size_t nr, size_t nc) { m = nr; n = nc; p = new double[m*n]; vCopy(a, p, m*n); } The declaration: Matrix A(a, 3, 3); would then construct a 3x3 matrix. In the process of building the matrix, we have transformed the shape of the data item from one-dimensional to two-dimensional. Does this seem a little strange? Couldn’t we, instead, deﬁne the array: double b[3][3] = {1, 2, 3, 4, 5, 6, 7, 8, 9}; Now, you and I and the designers of C and the ISO/IEC C++ Standards Committee know that the two declarations have identical results. The C language doesn’t www.embedded.com | embedded systems design | JUNE 2008 15 http://www.embedded.com

Table of Contents Feed for the Digital Edition of Embedded Systems Design - June 2008

Embedded Systems Design - June 2008 Contents #Include Party Bit Programmer's Toolbox Cover Feature: Virtual Hardware Platforms for Embedded Software Validation Allocating Memory in MATLAB-to-C Code MDD and IDEs: Making the Twain Meet in Embedded Systems Design Avoid a Thrashing Guest Editor Advertising Index Break Points Marketplace

Embedded Systems Design - June 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.