problem about indexToCells function of costmap2d

[youha...@gmail.com]

when I saw the costmap_2d.h, I got the definition of indexToCells is as follows:

inline void indexToCells(unsigned int index,unsigned int& mx,unsigned int& my) const

{

my=index/size_x_;

mx=index-(my*size_x_);

}

if my=index/size_x_,so mx=index-(my*size_x_)=index-(index/size_x_*size_x_)=index-index=0.In conlusion,mx=0.

I can´t understand why mx is zero?And if mx is zero,why can we set it to zero directly?

[David Lu!!]

The values are stored in row-major order, where rows equate to y
values. https://en.wikipedia.org/wiki/Row-_and_column-major_order

In your math, you're not taking the integer arithmetic into
consideration. There's an implicit casting happening such that my is
really int(index/size_x_)

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