}
checkfiles(const char *infile, const char *outfile){  struct stat buf;  if(infile)			/* infile ! = NULL */    if(stat(infile,&buf) < 0)      {	perror(infile);	crash();      };  if (outfile) {    if (stat(outfile, &buf) < 0)      return;			/* file does not exist */    else {      f_print(stderr,	      "file '%s' already exists and may be overwritten\n", outfile);      crash();    }  }}