How to memset a 2D arrray?

Question

I want to memset a 2D array to 0. Here's my code.. But it always giving me seg fault;

      bool **visited=new bool*[m];
         for(int i=0;i<m;++i)
           visited[i] = new bool[m];

I have tried memset(visited, 0, sizeof(visited[0][0]) * m * m); and memset(visited, 0, sizeof visited); , But nonw of this works and gives me segfault. how do I do that?

If you are using STL you should try using vector instead of array of booleans. http://en.cppreference.com/w/cpp/container/vector_bool — TomF, Aug 23 '13 at 20:13

David Heffernan · Accepted Answer · 2013-08-23T20:12:36.167

7

Your array is not contiguous since it is not actually a multi-dimensional array. It's an array of arrays, sometimes known as a jagged array.

So, your rows can, and will, be disjoint. Hence you'll need to call memset on each row.

bool **visited=new bool*[m];
for(int i=0;i<m;++i)
{
    visited[i] = new bool[m];
    memset(visited[i], 0, sizeof(visited[i][0]) * m);
}

Although, I can't refrain from pointing out that you should probably be using C++ features rather than writing what appears to be C with the use of the new operator.

edited Aug 23 '13 at 20:12

answered Aug 23 '13 at 20:07

David Heffernan

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Indeed, C++ should be utilized more. ;-) – László Papp Aug 23 '13 at 20:14
What C++ feature should I use? vector > ? – Tamim Addari Aug 24 '13 at 04:35
http://stackoverflow.com/questions/12841170/how-to-define-a-2d-array-in-c-and-stl-without-memory-manipulation but even if you used pointers there are smart pointers, and std::fill – David Heffernan Aug 24 '13 at 05:03

How to memset a 2D arrray?

1 Answers1