【IAR警告】Warning[Pa082]: undefined behavior: the order of volatile accesses is undefined

 

Warning[Pa082]: undefined behavior: the order of volatile accesses is undefined in this statement

 

運算符兩邊都是volatile變量的警告

 

這警告有意義.

用volatile修飾的變量一般不直接參與運算，volatile就以為着這個變量在運算過程中有可能已經改變了

例如：想計算a * b 要這樣:

volatile unsigned char a;
volatile unsigned char b;

unsigned char x,y;

x = a;
y = b;

return (x * y);

建議使用另外一個變量參與計算：

volatile char VVV = 9;

char fun()
{
       char xxx;
       char yyy = 9;

       xxx = VVV;
       return xxx * yyy
}