Actually A(b) with the example you have given will return [13 14 2 14 10]. That is the elements are taken from the first column of A. Note that using linear indexing (indexing a two dimension array with a vector of indices, rather the pairs of indices) will provide the elements columnwise.
I'm not clear whether this is what you are asking. What do you mean by get element C by index in vector A(b) ?