<div dir="ltr"><div><div><div><div>Hello Cyril,<br><br></div>Thank you for pointing out this behavior. This is a memory allocation problem in your program. To need to create some memory space to save the data that is returned by the vnl_matrix.<br></div>See below a way to solve your issue.<br></div><br>Hope this helps,<br></div>Francois<br><div><div><br>#include <iostream><br>#include <vnl_vector.h><br>#include <vnl_matrix.h><br>#include <cstring><br><br>int main()<br>{<br> vnl_matrix<double> matrix(2, 2);<br> matrix.put(0, 0, 4);<br> matrix.put(0, 1, 3);<br> matrix.put(1, 0, 2);<br> matrix.put(1, 1, 1);<br><br> // Display the matrix<br> std::cout << "Matrix" << std::endl;<br> std::cout << matrix << std::endl;<br><br> // Display the first row of the matrix,<br> vnl_vector<double> matrixRow;<br> matrixRow = matrix.get_row(0);<br> std::cout << "First row, stored in a vnl_vector" << std::endl;<br> std::cout << matrixRow << std::endl;<br><br> double matrixRowData[2];<br> std::memcpy(matrixRowData, matrix.get_row(0).data_block(), 2*sizeof(double));<br> std::cout << "First row, stored in a double*" << std::endl;<br> std::cout << matrixRowData[0] << " " << matrixRowData[1] << std::endl;<br><br> double* matrixRowDataFromVector = matrixRow.data_block();<br> std::cout << "First row, stored in a double* after passing through a vnl_vector" << std::endl;<br> std::cout << matrixRowDataFromVector[0] << " " << matrixRowDataFromVector[1] << std::endl;<br><br> return 0;<br>}<br><br>
<p style="margin:0px;text-indent:0px"><span style="font-family:"monospace";font-size:9pt;color:rgb(0,0,0)">Matrix</span></p>
<p style="margin:0px;text-indent:0px"><span style="font-family:"monospace";font-size:9pt;color:rgb(0,0,0)">4 3 </span></p>
<p style="margin:0px;text-indent:0px"><span style="font-family:"monospace";font-size:9pt;color:rgb(0,0,0)">2 1 </span></p>
<p style="margin:0px;text-indent:0px;font-family:"monospace";font-size:9pt;color:rgb(0,0,0)"><br></p>
<p style="margin:0px;text-indent:0px"><span style="font-family:"monospace";font-size:9pt;color:rgb(0,0,0)">First row, stored in a vnl_vector</span></p>
<p style="margin:0px;text-indent:0px"><span style="font-family:"monospace";font-size:9pt;color:rgb(0,0,0)">4 3</span></p>
<p style="margin:0px;text-indent:0px"><span style="font-family:"monospace";font-size:9pt;color:rgb(0,0,0)">First row, stored in a double*</span></p>
<p style="margin:0px;text-indent:0px"><span style="font-family:"monospace";font-size:9pt;color:rgb(0,0,0)">4 3</span></p>
<p style="margin:0px;text-indent:0px"><span style="font-family:"monospace";font-size:9pt;color:rgb(0,0,0)">First row, stored in a double* after passing through a vnl_vector</span></p>
<p style="margin:0px;text-indent:0px"><span style="font-family:"monospace";font-size:9pt;color:rgb(0,0,0)">4 3</span></p><br></div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Fri, Nov 4, 2016 at 10:26 AM, Cyril Mory <span dir="ltr"><<a href="mailto:cyril.mory@creatis.insa-lyon.fr" target="_blank">cyril.mory@creatis.insa-lyon.fr</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
Hello, ITK users,<br>
<br>
I've encountered a behavior with vnl_matrix, and I'm wondering
whether it is a bug or a feature. The following code outputs
differents results:<br>
<br>
#include <iostream><br>
#include <vnl_vector.h><br>
#include <vnl_matrix.h><br>
<br>
int main()<br>
{<br>
vnl_matrix<double> matrix(2, 2);<br>
matrix.put(0, 0, 4);<br>
matrix.put(0, 1, 3);<br>
matrix.put(1, 0, 2);<br>
matrix.put(1, 1, 1);<br>
<br>
// Display the matrix<br>
std::cout << "Matrix" << std::endl;<br>
std::cout << matrix << std::endl;<br>
<br>
// Display the first row of the matrix,<br>
vnl_vector<double> matrixRow;<br>
matrixRow = matrix.get_row(0);<br>
std::cout << "First row, stored in a vnl_vector" <<
std::endl;<br>
std::cout << matrixRow << std::endl;<br>
<br>
double* matrixRowData = matrix.get_row(0).data_block()<wbr>;<br>
std::cout << "First row, stored in a double*" <<
std::endl;<br>
std::cout << matrixRowData[0] << " " <<
matrixRowData[1] << std::endl;<br>
<br>
double* matrixRowDataFromVector = matrixRow.data_block();<br>
std::cout << "First row, stored in a double* after passing
through a vnl_vector" << std::endl;<br>
std::cout << matrixRowDataFromVector[0] << " "
<< matrixRowDataFromVector[1] << std::endl;<br>
<br>
return EXIT_SUCCESS;<br>
}<br>
<br>
Output : <br>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"><span style="font-family:'Monospace';font-size:9pt;color:#31363b">Matrix</span></p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"><span style="font-family:'Monospace';font-size:9pt;color:#31363b">4 3 </span></p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"><span style="font-family:'Monospace';font-size:9pt;color:#31363b">2 1 </span></p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px;font-family:'Monospace';font-size:9pt;color:#31363b">
</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"><span style="font-family:'Monospace';font-size:9pt;color:#31363b">First row, stored in a vnl_vector</span></p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"><span style="font-family:'Monospace';font-size:9pt;color:#31363b">4 3</span></p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"><span style="font-family:'Monospace';font-size:9pt;color:#31363b">First row, stored in a double*</span></p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"><span style="font-family:'Monospace';font-size:9pt;color:#31363b">0 3</span></p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"><span style="font-family:'Monospace';font-size:9pt;color:#31363b">First row, stored in a double* after passing through a vnl_vector</span></p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"><span style="font-family:'Monospace';font-size:9pt;color:#31363b">4 3</span></p>
<br>
<br>
It was compiled with the following CMakeLists.txt:<br>
<br>
<br>
cmake_minimum_required(VERSION 2.8)<br>
<br>
project(IsThisAvnlBug)<br>
<br>
find_package(ITK REQUIRED)<br>
include(${ITK_USE_FILE})<br>
<br>
add_executable(IsThisAvnlBug MACOSX_BUNDLE IsThisAvnlBug.cxx)<br>
target_link_libraries(<wbr>IsThisAvnlBug ${ITK_LIBRARIES})<br>
<br>
</div>
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