C++ instance resolution of pointer to function

C++ function Pointers are generally Pointers to functions, not to objects. Just like any other pointer, a function pointer points to a particular type. The function type is determined by its return type and the parameter list, regardless of the function name.

Definition:

char  ( *fP ) ( char . int ) ; 

Assignment:

char function(char i . int j)
{

} 

Fp = function;
call
(* fp) (10100);

type char (*FUN)(char . int);//The type definition
FUN fp ;//Define fp as a pointer to a function

The use and action of volatile :

Const is the opposite of volatile,
Volatile means that the value in the memory can change at any time.

uchar a . b . c 
a=5; 
b=a; //b=5 
c=a; //c=5 
volatile uchar a . b . c 
a=5; 
b=a; //B not sure
c=a; //C not sure

For example, the P0 port of SCM is initialized as:

P0=0x0000 0001 
a=p0; //If the P0 port is artificially connected to a high level, a=0x1111 1111 instead of 0x0000 0001. hardware-related

Volatile is often used when defining the address of a register:

#define rGPCCON  (*(volatile unsigned *)0x56000020)    
#define rGPCDAT  (*(volatile unsigned *)0x56000024) 

In a project with a large number of files, minimize the use of global variables and use the function call form directly

Single file: static   char   I;   Define static variables to prevent unexpected changes to the values of variables by other files.

char fun(void)
{ 
  return(i); 
} 

Directly call the global variable form: extern int I;     Such a disadvantage is that there is a hidden danger, when the file is more likely to appear the global variable name problem, at this time to modify the words may be more trouble.