我这段 C 代码可以在编译时候输出结构体的大小，你们还有什么好点子， show me the code!

[Exxfire]

#include <stdio.h>

struct X
{
    int a;
    char c[10];
    short d;
};
char checker(int a)
{
    (void)a;
    return '1';
}

#define STRINGIFY(x) #x
#define TOSTRING(x) STRINGIFY(x)

#define TEST(x)                                                              \
    do                                                                       \
    {                                                                        \
        char checkSizeOfInt[sizeof(x)] = {checker(&checkSizeOfInt)};         \
        _Pragma(TOSTRING(message("Value: " #x)))                             \
    } while (0);

int main() {
    TEST(struct X);
    return 0;
}

[pipapa]

哪些编译器可以

[Exxfire]

@pipapa 我用的 gcc 编译，其它没试。gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.12)

[henix]

在 gcc 14 上修改之后会输出这些：

···
test.c: In function 'main':
test.c:21:51: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
21 | char checkSizeOfInt[sizeof(x)] = {checker((int)&checkSizeOfInt)}; \
| ^
test.c:26:5: note: in expansion of macro 'TEST'
26 | TEST(struct X);
| ^~~~
test.c:22:9: note: '#pragma message: Value: struct X'
22 | _Pragma(TOSTRING(message("Value: " #x))) \
| ^~~~~~~
test.c:26:5: note: in expansion of macro 'TEST'
26 | TEST(struct X);
| ^~~~
···

没看到什么结构体大小啊

[open9527]

有什么用吗

[csfreshman]

没什么用，执行和 3 楼一样

[Exxfire]

@henix
var_para_num_test.c: In function ‘main’:
var_para_num_test.c:21:51: warning: passing argument 1 of ‘checker’ makes integer from pointer without a cast [-Wint-conversion]
char checkSizeOfInt[sizeof(x)] = {checker(&checkSizeOfInt)}; \
^
var_para_num_test.c:26:5: note: in expansion of macro ‘TEST’
TEST(struct X);
^
var_para_num_test.c:9:6: note: expected ‘int’ but argument is of type ‘char (*)[16]’
char checker(int a)
^
var_para_num_test.c:26:17: note: #pragma message: Value: struct X
TEST(struct X);
^
var_para_num_test.c:21:36: note: in definition of macro ‘TEST’
char checkSizeOfInt[sizeof(x)] = {checker(&checkSizeOfInt)};

[yolee599]

https://stackoverflow.com/a/53884709
但是有什么用呢？

[Exxfire]

@yolee599 在编译阶段获取信息意味着不用等待程序编译完成，并执行，可以节省时间，提升效率。
当然，我只是觉得这么干很有意思。