需要左值的左值

Question

同时编译此代码：

#define SET_BIT(reg,bitno)          reg|=(1<<bitno)
#define CLR_BIT(reg,bitno)          reg &=~(1<<bitno)
#define GET_BIT(reg,bitno)          ((reg>>bitno)&1)
#define TOGGLE_BIT(reg,bitno)       reg^=(1<<bitno)

switch (PIN_select){

     case DIO_PIN_A:
        if (level==LOW)
            CLR_BIT(DIO_PIN_A,PIN_Bit);
        else if(level==HIGH)
            SET_BIT(DIO_PIN_A,PIN_Bit);
     break;
}

我遇到以下错误：

 error: lvalue required as left operand of assignment fac(0)=1;
 error: lvalue required as left operand of assignmen
 error: lvalue required as left operand of assignment
 #define CLR_BIT(REG,BIT) REG &=~(1<<BIT)
                              ^
 note: in expansion of macro ‘CLR_BIT’
CLR_BIT(DIO_PIN_A,PIN_Bit);
    ^
 error: lvalue required as left operand of assignment
 #define SET_BIT(REG,BIT) REG|=(1<<BIT)
                             ^

Answer 1

例如，此行

CLR_BIT(DIO_PIN_A,PIN_Bit);

扩展到：

DIO_PIN_A &= ~(1<<PIN_Bit);

但是，DIO_PIN_A是整数常数（我们知道，因为在case中使用了它，所以您不能对其进行修改。