+ FILE *fp = fopen(filename, "r");
+ if (fp) {
+ int ret;
+ char buffer[FILENAME_MAX+80];
+ fclose(fp);
+ sprintf(buffer, "Overwrite existing file\n%.*s?",
+ FILENAME_MAX, filename);
+ ret = MessageBox(hwnd, buffer, "PuTTYgen Warning",
+ MB_YESNO | MB_ICONWARNING);
+ if (ret != IDYES)
+ break;
+ }