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POSegmentation Fault while using two-dimensional array of pointers
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  1. POSegmentation Fault while using two-dimensional array of pointers
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    copied!<p>Hey there, this is turning out to really be a tricky one for me.</p> <p><em><strong>main.cpp</em></strong></p> <pre><code>#include &lt;stdlib.h&gt; #include &lt;iostream&gt; #include "Matrix.h" int main(int argc, char** argv) { // Dummy matrix double row1[3] = {3, -1, -2}; double col1[3] = {4, 3, 1}; // Initialize matrix with 4 x 2 dimensions Matrix&lt;double&gt; *m = new Matrix&lt;double&gt;(1, 3); Matrix&lt;double&gt; *n = new Matrix&lt;double&gt;(3, 1); Matrix&lt;double&gt; *mn; // Set each row or column m-&gt;set_row(row1, 0); n-&gt;set_col(col1, 0); std::cout &lt;&lt; "Matrix M: \n"; m-&gt;print(); std::cout &lt;&lt; "Matrix N: \n"; n-&gt;print(); std::cout &lt;&lt; "Matrix MN: \n"; mn = m-&gt;mult(n); mn-&gt;print(); return (EXIT_SUCCESS); } </code></pre> <p><em><strong>matrix.h</em></strong></p> <pre><code>/* * File: Matrix.h * Author: charles * * Created on March 16, 2011, 12:45 AM */ #ifndef _MATRIX_H_ #define _MATRIX_H_ template &lt;typename T&gt; class Matrix { public: Matrix(int _r, int _c){ // Set row and column size, then initialize matrix _rows = _r; _cols = _c; _matrix = new T * [_rows]; for(int i = 0; i &lt; _rows; ++i){ _matrix[i] = new T [_cols]; } } virtual ~Matrix(){ // Delete everything for(int i = 0; i &lt; _cols; ++i){ delete[] _matrix[i]; } delete[] _matrix; } // Get number of rows unsigned int get_rows(){ return _rows; } // Get number of columns unsigned int get_cols(){ return _cols; } // Returns the row from _matrix as an array T* get_row(int _r){ T* _t = new T [_cols]; for(int i = 0; i &lt; _cols; ++i){ _t[i] = _matrix[_r][i]; } return _t; } // Returns the column from _matrix as an array T* get_col(int _c){ T* _t = new T [_rows]; for(int i = 0; i &lt; _rows; ++i){ _t[i] = _matrix[i][_c]; } return _t; } T get_elem(int _r, int _c){ return _matrix[_r][_c]; } // Set a specific row with an array of type T void set_row( T _t[], int _r ){ for(int i = 0; i &lt; _cols; ++i){ _matrix[_r][i] = _t[i]; } } // Set a specific column with an array of type T void set_col( T _t[], int _c){ for(int i = 0; i &lt; _rows; ++i){ _matrix[i][_c] = _t[i]; } } // Set a specific index in the matrix with value T void set_elem(T _t, int _r, int _c){ _matrix[_r][_c] = _t; } // Test to see if matrix is square bool is_square(){ return (_rows == _cols); } // Print contents of matrix for debugging purposes void print(){ for(int i = 0; i &lt; _rows; ++i){ for(int j = 0; j &lt; _cols; ++j){ std::cout &lt;&lt; _matrix[i][j] &lt;&lt; " "; } std::cout &lt;&lt; "\n"; } } T comp_mult(int _r, T* _c){ T temp; for(int i = 0; i &lt; _cols; ++i){ std::cout &lt;&lt; "Comp " &lt;&lt; i &lt;&lt; "\n"; if(i == 0) temp = _matrix[_r][i] * _c[i]; else temp += _matrix[_r][i] * _c[i]; } return temp; } // Add one matrix to another and return new matrix Matrix* add(Matrix* _m){ // Cannot add matrices if they do not have the same dimensions if(!(_rows == _m-&gt;get_rows() &amp;&amp; _cols == _m-&gt;get_cols())){ std::cout &lt;&lt; "Not equal!"; return NULL; } else{ Matrix&lt;T&gt;* _t = new Matrix&lt;T&gt;(_rows, _cols); for(int i = 0; i &lt; _rows; ++i){ for(int j = 0; j &lt; _cols; ++j){ _t-&gt;set_elem(_matrix[i][j] + _m-&gt;get_elem(i, j), i, j); } } return _t; } } // Multiply two matrices and return new matrix Matrix* mult(Matrix* _m){ // If dimensions are not compatible return NULL if(_cols != _m-&gt;get_rows()){ return NULL; } else{ Matrix&lt;T&gt;* _t = new Matrix&lt;T&gt;(_rows, _m-&gt;get_cols()); // Print out dimensions // std::cout &lt;&lt; "Dimensions: r = " &lt;&lt; _t-&gt;get_rows() &lt;&lt; " c = " &lt;&lt; _t-&gt;get_cols() &lt;&lt; "\n"; // Each row of _t for(int i = 0; i &lt; _t-&gt;get_rows(); ++i){ // Each value in each row of _t for(int j = 0; j &lt; _t-&gt;get_cols(); ++j){ T temp; // Temp variable to hold value for _t[i][j] // Each row in _matrix std::cout &lt;&lt; "Loop i:" &lt;&lt; i &lt;&lt; "\n"; temp = this-&gt;comp_mult(i, _m-&gt;get_col(j)); std::cout &lt;&lt; "loop j: " &lt;&lt; j &lt;&lt; "\n"; std::cout &lt;&lt; "TEMP = " &lt;&lt; temp &lt;&lt; "\n"; _t-&gt;set_elem(temp, i, j); // this is where i segfault } } } } // Multiply entire matrix by number and return new matrix Matrix* scalar(T _n){ Matrix&lt;T&gt;* _t = new Matrix&lt;T&gt;(_rows, _cols); for(int i = 0; i &lt; _rows; ++i){ for(int j = 0; j &lt; _cols; ++j){ _t-&gt;set_elem(_matrix[i][j] * _n, i, j); } } return _t; } private: unsigned int _rows; // Number of rows unsigned int _cols; // Number of columns T** _matrix; // Actual matrix data }; #endif /* _MATRIX_H_ */ </code></pre> <p><em><strong>Sample Output</em></strong></p> <pre><code>Matrix M: 3 -1 -2 Matrix N: 4 3 1 Matrix MN: Loop i:0 Comp 0 Comp 1 Comp 2 loop j: 0 TEMP = 7 Segmentation fault </code></pre> <p>So the problem I'm having is that I am getting a segmentation fault when trying to assign a new matrix a value. It does not make sense to me because I have initialized the new matrix that I am trying to assign a value, I know its size, I'm not trying to access memory outside the matrix, and I know that my temp variable has a value. Anyone with a suggestion? </p>
 

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