error: no default constructor exists for class

What could be the reason for this behavior? The SparseMatrix class does not exist, there is only a SparseMatrix structure. I use Qt Creator 4.9.0, CMake 3.10.2, C ++, CUDA, Ubuntu 18.04.

sparsematrix.h

#pragma once #include <iostream> #include <unordered_map> #include <string> #include <regex> #include <fstream> #include <vector> typedef std::unordered_map<size_t,double> IndexValue; typedef std::unordered_map<std::size_t,IndexValue> Matrix; struct SparseMatrix { SparseMatrix(const std::string &A,const std::string &B) { std::ifstream in(A); std::string line; std::getline(in,line);//считали шапку in>>m_nrows; m_ncols = m_nrows+1; std::getline(in,line);//считали значение std::getline(in,line);//считали шапку-2 while(in) { std::size_t i,j; double val; in>>i>>j>>val; m_matrix[i][j] = val; } in.close(); in.open(B); std::getline(in,line); std::getline(in,line); std::getline(in,line); while(in) { std::size_t i; double val; in>>i>>val; m_matrix[i][m_nrows] = val; } std::cout<<m_matrix.size()<<'\n'; } SparseMatrix(const Matrix &matrix,std::size_t s1,std::size_t s2) { m_matrix = matrix; m_nrows = s1; m_ncols = s2; } void print() { for(std::size_t i = 0; i<m_nrows; i++) { for(std::size_t j = 0; j<m_ncols; j++) std::cout<<m_matrix[i][j]<<' '; std::cout<<'\n'; } } double get(std::size_t i,std::size_t j) { return m_matrix[i][j]; } std::vector<double> get_column(std::size_t j) { std::vector<double> R(m_nrows); for(std::size_t i = 0; i<m_nrows; i++) { R[i] = m_matrix[i][j]; } return R; } void set(double val,std::size_t i,std::size_t j) { m_matrix[i][j] = val; } std::size_t m_nrows; std::size_t m_ncols; private: Matrix m_matrix; }; 

particle.cu (30): - 1: error: error: no default constructor exists for class "SparseMatrix"