template<classT>classgslice_array;std::gslice_array is a helper template used by the
with std::gslice argument. It has reference semantics to a subset of the array specified by the std::gslice object.
Member types
Type Definition value_typeTMember functions
Example
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#include<cassert>#include<cstddef>#include<iomanip>#include<iostream>#include<numeric>#include<valarray>intmain(){std::valarray<int>data(32);std::iota(std::begin(data),std::end(data),0);conststd::size_toffset=1,z=2,y=3,x=4;conststd::valarray<std::size_t>sizes{z,y,x};conststd::valarray<std::size_t>strides{15,5,1};conststd::gslicegslice=std::gslice(offset,sizes,strides);// Indices are generated according to the formula:// index[k] = offset + [0,1,2)*15 + [0,1,2,3)*5 + [0,1,2,3,4)*1// = offset + inner_product(sizes[k], strides);// where sizes[k] = {[0,z), [0,y), [0,x)}, while the rightmost index (x)// runs fastest. As a result we have following set of indices:// index[0] = 1 + 0*15 + 0*5 + 0*1 = 1// index[1] = 1 + 0*15 + 0*5 + 1*1 = 2// index[2] = 1 + 0*15 + 0*5 + 2*1 = 3// index[3] = 1 + 0*15 + 0*5 + 3*1 = 4// index[4] = 1 + 0*15 + 1*5 + 0*1 = 6// index[5] = 1 + 0*15 + 1*5 + 1*1 = 7// index[6] = 1 + 0*15 + 1*5 + 2*1 = 8// index[7] = 1 + 0*15 + 1*5 + 3*1 = 9// ...// index[22] = 1 + 1*15 + 2*5 + 2*1 = 28// index[23] = 1 + 1*15 + 2*5 + 3*1 = 29conststd::valarray<int>indices=data[gslice];for(unsignedi=0;i!=indices.size();++i)std::cout<<std::setfill('0')<<std::setw(2)<<indices[i]<<' ';std::cout<<"\nTotal indices: "<<indices.size()<<'\n';assert(indices.size()==x*y*z);data=0;std::gslice_array<int>gslice_array=data[gslice];gslice_array=1;// Cells that correspond to generated indices = '1', skipped cells = '0'.for(autoi:data)std::cout<<i<<' ';std::cout<<"\nSum of ones = "<<data.sum()<<'\n';}Output:
01 02 03 04 06 07 08 09 11 12 13 14 16 17 18 19 21 22 23 24 26 27 28 29 Total indices: 24 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 0 Sum of ones = 24 See also
proxy to a subset of a valarray after applying a slice
(class template)
(C++23)
a multi-dimensional non-owning array view
(class template)