Question

尝试如下嵌套宏调用：

#include <stdint.h>

#define INT
#define LONG

#define AS(t) AS_##t
#define AS_INT as_int
#define AS_LONG as_long

#define LET(v, t) v. AS(t)

typedef union
{
    int32_t as_int;
    int64_t as_long;
} mytype_t;

int main()
{
    mytype_t s;

    s.AS(INT) = 10;    /* This is OK */

    LET(s, INT) = 10;  /* This makes error */

    return 0;
}

出现错误：

main.c:xx:yy: error: ‘mytype_t {aka union <anonymous>}’ has no member named ‘AS_’
 #define LET(v, t) v. AS(t)
                    ^
main.c:zz:ww: note: in expansion of macro ‘LET’
     LET(s, INT) = 10;
     ^~~

是否有任何变通办法可以使用LET(s, INT) = 10;？

Answer 1

这是这两个 empty 宏

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    <meta charset="<?php echo Yii::$app->charset ?>">
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#define INT #define LONG通过INT传递到AS(t)时经历中间扩展，并在扩展LET之前扩展为空令牌序列。这样，您将AS()与空令牌序列连接在一起。只需删除这两个宏，为您的示例定义AS_和AS_INT就足够了。

Answer 2

已经回答该错误是由于空宏造成的。

另一个解决方案可以是：

#define INT INT
#define LONG LONG

希望这会有所帮助。

嵌套宏调用

2 个答案: