結構體中進行宏定義的意圖

在定義結構體時進行宏定義，其作用域從定義處開始直至文件結束

與結構體外的同名宏定義會有redefine的warning，新的定義會覆蓋之前的定義

其作用是告知源代碼閱讀者，該宏定義是爲了該結構體中變量而定定義，如下代碼中，MAY和JUNE宏定義是用於變量month使用。

#include<stdio.h>

#define MAY 0
typedef struct test
{
    int month;
#define  MAY 5
#define JUNE 6
    int day;
}TEST;

#define JUNE 0

int main()
{
    TEST a;

    printf("&month = %x\n&day = %x\nMAY = %d\nJUNE = %d\n", &a.month, &a.day, MAY, JUNE);

    return 0;
}

關於宏定義，如下告警

testmacro.c:7:0: warning: "MAY" redefined [enabled by default]
 #define  MAY 5
 ^
testmacro.c:3:0: note: this is the location of the previous definition
 #define MAY 0
 ^
testmacro.c:12:0: warning: "JUNE" redefined [enabled by default]
 #define JUNE 0
 ^
testmacro.c:8:0: note: this is the location of the previous definition
 #define JUNE 6
 ^

程序運行結果如下

&month = 99f791e0
&day = 99f791e4
MAY = 5
JUNE = 0