【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

 

运算符两边都是volatile变量的警告

 

这警告有意义.

用volatile修饰的变量一般不直接参与运算，volatile就以为着这个变量在运算过程中有可能已经改变了

例如：想计算a * b 要这样:

volatile unsigned char a;
volatile unsigned char b;

unsigned char x,y;

x = a;
y = b;

return (x * y);

建议使用另外一个变量参与计算：

volatile char VVV = 9;

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

       xxx = VVV;
       return xxx * yyy
}