C语言宏定义时#(井号)和##(双井号)的用法

#include <iostream>
void quit_command(){
printf("I am quit command\n");
}
void help_command(){
printf("I am help command\n");
}
struct command
{
char * name;
void (*function) (void);
};
#define COMMAND(NAME) {#NAME,NAME##_command}
#define PRINT(NAME) printf("token"#NAME"=%d\n", token##NAME)
main(){
int token9=9;
PRINT(9);
struct command commands[] = {
COMMAND(quit),
COMMAND(help),
};
commands[0].function();
}