用IAR测试stm8s003的printf，无法打印小数点是怎么回事？

如题，无法输出小数点，IAR还要怎么设置？？
double y=0;
y=34.56;
printf("rn Printf_Number1 = %0.1f rn", y);

int fputc(int ch, FILE *f)
{
  Uart1_SendData(ch);
  return ch;
}