Help me see. It seems that I have never seen such a definition

57223387

#define XBYTE ((unsigned char volatile xdata *) 0)

What does this definition mean:

hzxszmh

Unsigned char volatile xdata type pointer, the pointer value is 0;

珈蓝易拉罐

It is to define a macro, which is equivalent to a null pointer, but the pointer is converted to point to unsigned char volatile xdata type.
Volatile is very similar to const, both are restrictors, and the meaning is just the opposite. One is constant and the other is variable (it may change in the program if it seems to be unchanged. It is mostly used to modify multi-threaded shared variables to prevent the compiler Misunderstood that it does not change and make some optimization)

julines

((unsigned char volatile xdata *) 0) is a null pointer of type unsigned char
volatile is to remind the compiler not to optimize access to this variable, because it may be modified by another thread.

zfy010317

Define a pointer. The name is xdata;
The type is: unsigned char volatile *
The initial value is: 0
Among them, volatile means that the compiler does not optimize the value.

zfy010317

Oh.
What is xdata?
Haha

xpyuanfly

I haven't seen this kind of define. It seems that after the 0 is added later, this XBYTE is not easy to use.

诃梨勒

Define a pointer. The name is xdata;
The type is: unsigned char volatile *
The initial value is: 0
=============================================
I have never seen such an initial value, and the test failed



Among them, volatile means that the compiler does not optimize the value.
=============================================
Note that when the compiler does not optimize, volatile may not work, but when you start optimizing code (when the compiler starts looking for redundant reads), you can prevent major errors.
(From "C++ Programming Ideas Volume One 2nd Edition" P73)

LZ may wish to send out the code that refers to this macro to see

天魔狂舞

xdata refers to a pointer to the xdata area.