关于宏的 ## 与 #

#include<cstdio>
#include<climits>
using namespace std; 
#define STR(s)     #s
#define CONS(a,b)  int(a##e##b)
int main()
{
    printf(STR(vck));           // 输出字符串"vck"
    printf("%d/n", CONS(2,3));  // 2e3 输出:2000
    return 0;
}

#define TOW      (2)
#define MUL(a,b) (a*b)
printf("%d*%d=%d/n", TOW, TOW, MUL(TOW,TOW));

printf("%d*%d=%d/n", (2), (2), ((2)*(2)));

#define A          (2)
#define STR(s)     #s
#define CONS(a,b)  int(a##e##b)
printf("int max: %s/n",  STR(INT_MAX));    // INT_MAX ＃i nclude<climits>

printf("int max: %s/n", "INT_MAX");
printf("%s/n", CONS(A, A));               // compile error 
这一行则是：
printf("%s/n", int(AeA));

#define A           (2)
#define _STR(s)     #s
#define STR(s)      _STR(s)          // 转换宏
#define _CONS(a,b)  int(a##e##b)
#define CONS(a,b)   _CONS(a,b)       // 转换宏
printf("int max: %s/n", STR(INT_MAX));          // INT_MAX,int型的最大值，为一个变量 ＃i nclude<climits>
输出为: int max: 0x7fffffff
STR(INT_MAX) -->  _STR(0x7fffffff) 然后再转换成字符串；
printf("%d/n", CONS(A, A));
输出为：200
CONS(A, A)  -->  _CONS((2), (2))  --> int((2)e(2))

#define  ___ANONYMOUS1(type, var, line)  type  var##line
#define  __ANONYMOUS0(type, line)  ___ANONYMOUS1(type, _anonymous, line)
#define  ANONYMOUS(type)  __ANONYMOUS0(type, __LINE__)

#define  FILL(a)   {a, #a}
enum IDD{OPEN, CLOSE};
typedef struct MSG{
  IDD id;
  const char * msg;
}MSG;
MSG _msg[] = {FILL(OPEN), FILL(CLOSE)};
相当于：
MSG _msg[] = {{OPEN, "OPEN"},
              {CLOSE, "CLOSE"}};

#define  _GET_FILE_NAME(f)   #f
#define  GET_FILE_NAME(f)    _GET_FILE_NAME(f)
static char  FILE_NAME[] = GET_FILE_NAME(__FILE__);

#define  _TYPE_BUF_SIZE(type)  sizeof #type
#define  TYPE_BUF_SIZE(type)   _TYPE_BUF_SIZE(type)
char  buf[TYPE_BUF_SIZE(INT_MAX)];
     -->  char  buf[_TYPE_BUF_SIZE(0x7fffffff)];
     -->  char  buf[sizeof "0x7fffffff"];