strncpy_s 和 strcat_s

char* p_source = "tianzhaixing.bin";
  unsigned int len = static_cast<unsigned int > (strlen(p_source) - 4);
  char* p_name = (char*) malloc(len);
  strncpy_s(p_name, len+1, p_source, len);
  strcat_s(p_name, len+5, ".txt");
  std::cout << "p_name:" << p_name << std::endl;