在编译时查看结构元素的大小？

Question

如何在编译时查看结构元素的大小？

我试过了：

#define XSTR(x) STR(x)
#define STR(x) #x
#pragma message "Size of struct: " XSTR(sizeof(my_struct.element))

但它只显示：

note: #pragma message: Size of struct: sizeof(my_struct.element)

我不想断言尺寸是否合适。我想知道尺码是多少

编辑：我没有问 "how do I use sizeof?"。（这是另一个 post 问的），所以我不认为它是重复的。我问“如何在编译时查看结构元素的大小？这是一个不同的问题。

我正在尝试解决为什么编译器将 32 位分配给 16 位结构。

Answer 1

很遗憾，我只能想出以下丑陋的 brute-force 方法。但他们工作。

方法一

在大小对应的行编译失败。通过检查哪一行失败，我知道结构元素的大小

#define STATIC_ASSERT_SIZE(an_item, a_siz) do { enum { dummy_var = 1/((an_item == a_siz)? 0 : 1 )}; } while (0)

STATIC_ASSERT_SIZE(sizeof(my_struct.element), 0);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 1);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 2);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 3);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 4);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 5);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 6);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 7);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 8);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 9);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 10);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 11);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 12);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 13);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 14);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 15);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 16);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 17);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 18);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 19);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 20);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 21);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 22);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 23);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 24);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 25);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 26);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 27);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 28);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 29);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 31);
STATIC_ASSERT_SIZE(sizeof(my_struct.element), 32);

方法二

假设编译成功，查看编译器生成的 MAP 文件中的变量，它告诉您它使用了多少字节。

在编译时查看结构元素的大小？

See the size of a struct element at compile time?

c

struct

sizeof