Eigen Map - does it take ownership of the data pointer?

Question

I'm creating a Matrix with the Map class:

float* d = new float[rows*cols];
// ... getting data into d
Eigen::Map<Eigen::MatrixXf>(d, rows, cols);         

My question is - does Map take ownership of the data pointer and deletes it when its done? or does it copy the data and should I free it myself after the Map is created?

Thanks.

Answer 1

Documentation is very sparse on this but apart from that it's more common to not delete what you have not created, posts like this one suggest you should delete d when you're ready.

I suggest to run a memory profiler like valgrind which would tell you in case the pointer has not been deleted.

In case you don't delete d valgrind reports:

400 bytes in 1 blocks are definitely lost in loss record 1 of 1
  in operator new[](unsigned long) in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so
  1: operator new[](unsigned long) in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so
  2: main in test

So you can be quite sure you have to delete your data (which is good).

Shame on that documentation...

Answer 2

No, Map does not take ownership so you are still responsible for freeing memory. Actually, the contrary would be impossible for several reasons:

• Map cannot know how the memory has been allocated
• You can map only a subrange of an allocated buffer

Moreover, the following would be very strange:

 float *d = new float[10];
 // ...
 VectorXf v = ...;
 v = v + Map<VectorXf>(d,10);
 // now d is a dead pointer

No way!