char* fn = a.ToNewCString();
char* fn = ToNewCString(a);
OpenRegressionFile(const nsString& aBaseName, const nsString& aOutputName){  nsAutoString a;  a.Append(aBaseName);  a.AppendWithConversion("/");  a.Append(aOutputName);  char* fn = a.ToNewCString();  FILE* fp = fopen(fn, "r");  if (!fp) {    printf("Unable to open regression data file %s\n", fn);  }  delete[] fn;  return fp;}