按键初始化如下：
void Key_Init(void)
{
EXTI_InitTypeDef   EXTI_InitStructure;
    GPIO_InitTypeDef   GPIO_InitStructure;
    NVIC_InitTypeDef   NVIC_InitStructure;

    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE); //使能IO时钟
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_SYSCFG, ENABLE);//使能SYSCFG时钟
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8 | GPIO_Pin_9 | GPIO_Pin_10 | GPIO_Pin_11; 
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_Speed= GPIO_Speed_50MHz;
GPIO_Init(GPIOD,&GPIO_InitStructure);

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_12 | GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15; 
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_DOWN;
GPIO_InitStructure.GPIO_Speed= GPIO_Speed_50MHz;
  GPIO_Init(GPIOD, &GPIO_InitStructure);

SYSCFG_EXTILineConfig(EXTI_PortSourceGPIOD, EXTI_PinSource12);//初始化中断线
SYSCFG_EXTILineConfig(EXTI_PortSourceGPIOD, EXTI_PinSource13);//初始化中断线
SYSCFG_EXTILineConfig(EXTI_PortSourceGPIOD, EXTI_PinSource14);//初始化中断线
SYSCFG_EXTILineConfig(EXTI_PortSourceGPIOD, EXTI_PinSource15);//初始化中断线

EXTI_ClearITPendingBit(EXTI_Line12);
EXTI_ClearITPendingBit(EXTI_Line13);
EXTI_ClearITPendingBit(EXTI_Line14);
EXTI_ClearITPendingBit(EXTI_Line15);

  EXTI_InitStructure.EXTI_Line = EXTI_Line12|EXTI_Line13|EXTI_Line14|EXTI_Line15;    //配置中断线为中断线
  EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;          //配置中断模式
  EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Rising;      //配置为上升沿触发
  EXTI_InitStructure.EXTI_LineCmd = ENABLE;                    //配置中断线使能
  EXTI_Init(&EXTI_InitStructure);                              

  NVIC_InitStructure.NVIC_IRQChannel = EXTI15_10_IRQn;             
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x0F; 
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x0F;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_Init(&NVIC_InitStructure);

GPIO_ResetBits(GPIOD,GPIO_Pin_12);
GPIO_ResetBits(GPIOD,GPIO_Pin_13);
GPIO_ResetBits(GPIOD,GPIO_Pin_14);
GPIO_ResetBits(GPIOD,GPIO_Pin_15);
}

PD8~PD11为键盘的列，PD12~PD15为键盘的行。

main.c如下，当检测到有按键按下，则开始扫描，并输出按下的是哪个键：
while(1)
{    
Delay(1000);

if(key_pressed_flag){
ReadValue=KEY_Scan();
if(ReadValue!=0){
 Delay(10);
if(ReadValue==KEY_Scan()){
printf("ReadValue=%d",ReadValue);
printf(" ");
}
else
printf("read error!");
}
key_pressed_flag=0;
}
}

中断函数如下：
void EXTI15_10_IRQHandler(void){
key_pressed_flag=1;

EXTI_ClearITPendingBit(EXTI_Line12);
EXTI_ClearITPendingBit(EXTI_Line13);
EXTI_ClearITPendingBit(EXTI_Line14);
EXTI_ClearITPendingBit(EXTI_Line15);
}

现在按下键盘，并没有输出，不知道问题出在哪里？求解答！！