这段代码说是实现了一个复制数据的函数，但是看不懂是什么意思，求大虾指点

const char *UserMohrModel::Copy(const ConstitutiveModel *cm) {
  
  const char *str = ConstitutiveModel::Copy(cm);
  if (str) return(str);
  UserMohrModel *mm = (UserMohrModel *)cm;
  dBulk = mm->dBulk;
  dShear = mm->dShear;
  dCohesion = mm->dCohesion;
  dFriction = mm->dFriction;
  dDilation = mm->dDilation;
  dTension = mm->dTension;
  dYoung = mm->dYoung;
  dPoisson = mm->dPoisson;
  return(0);

楼主到C++大板块问问吧