C语言#和##连接符在项目中的应用(漂亮)

之前看见ST官方一个老外的风格，看完之后大赞。
看看他是怎么写的:

#ifndef RINGBUFF_HDR_H
#define RINGBUFF_HDR_H

#ifdef __cplusplus
extern "C" {
#endif

#include 
#include 

/**
 * \defgroup        RINGBUFF Ring buffer
 * \brief           Generic ring buffer manager
 * \{
 */

/* --- Buffer unique part starts --- */
/**
 * \brief           Buffer function/typedef prefix string
 * 
 * It is used to change function names in zero time to easily re-use same library between applications.
 * Use `#define BUF_PREF(x)    my_prefix_ ## x` to change all function names to (for example) `my_prefix_buff_init` 
 *
 * \note            Modification of this macro must be done in header and source file aswell
 */
#define BUF_PREF(x)                     ring ## x
/* --- Buffer unique part ends --- */

/**
 * \brief           Buffer structure
 */
typedef struct {
    uint8_t* buff;                              /*!< Pointer to buffer data.
                                                    Buffer is considered initialized when `buff != NULL` and `size` */
    size_t size;                                /*!< Size of buffer data. Size of actual buffer is `1` byte less than value holds */
    size_t r;                                   /*!< Next read pointer. Buffer is considered empty when `r == w` and full when `w == r - 1` */
    size_t w;                                   /*!< Next write pointer. Buffer is considered empty when `r == w` and full when `w == r - 1` */
} BUF_PREF(buff_t);

uint8_t     BUF_PREF(buff_init)(BUF_PREF(buff_t)* buff, void* buffdata, size_t size);
void        BUF_PREF(buff_free)(BUF_PREF(buff_t)* buff);
void        BUF_PREF(buff_reset)(BUF_PREF(buff_t)* buff);

/* Read/Write functions */
size_t      BUF_PREF(buff_write)(BUF_PREF(buff_t)* buff, const void* data, size_t btw);
size_t      BUF_PREF(buff_read)(BUF_PREF(buff_t)* buff, void* data, size_t btr);
size_t      BUF_PREF(buff_peek)(BUF_PREF(buff_t)* buff, size_t skip_count, void* data, size_t btp);

/* Buffer size information */
size_t      BUF_PREF(buff_get_free)(BUF_PREF(buff_t)* buff);
size_t      BUF_PREF(buff_get_full)(BUF_PREF(buff_t)* buff);

/* Read data block management */
void *      BUF_PREF(buff_get_linear_block_read_address)(BUF_PREF(buff_t)* buff);
size_t      BUF_PREF(buff_get_linear_block_read_length)(BUF_PREF(buff_t)* buff);
size_t      BUF_PREF(buff_skip)(BUF_PREF(buff_t)* buff, size_t len);

/* Write data block management */
void *      BUF_PREF(buff_get_linear_block_write_address)(BUF_PREF(buff_t)* buff);
size_t      BUF_PREF(buff_get_linear_block_write_length)(BUF_PREF(buff_t)* buff);
size_t      BUF_PREF(buff_advance)(BUF_PREF(buff_t)* buff, size_t len);

#undef BUF_PREF         /* Prefix not needed anymore */

/**
 * \}
 */

#ifdef __cplusplus
}
#endif

#endif /* RINGBUFF_HDR_H */

这个老外实现的是一个环形缓冲，然而他巧妙的将ring这个字串去掉，最后阅读代码看到的是非常整齐的：

BUF_PREF(buffer_init)
BUF_PREF(buff_free)
BUF_PREF(buff_write)
BUF_PREF(buff_read)
等等。。。

#define BUF_PREF(x) ring ## x
"##" 表示将左边的字符串和右边的字符串连接起来，但是只能黏贴C语言除了关键字以外的合法标识符
于是上面展开的效果如下：

ring_buffer_init
ring_buffer_free
ring_buffer_write
ring_buffer_read
等等。。。

既然知道了原理，那我在项目上可以这么来用。
之前，你写个LED驱动或者别的可能是这样的，定义了这么多个函数

void led_device_open(void);
void led_device_close(void);
uint8_t led_device_read(void);
uint8_t led_device_write(uint8_t status);
。。。

看起来很统一，我一眼看出这是一个LED的操作方法，但操作一个LED不就是

open，close，read，write方法吗？

我们可以让它看起来更优雅

#define  LED_CLASS(x) led_device_ ## x
void     LED_CLASS(open)(void);
void     LED_CLASS(close)(void);
uint8_t  LED_CLASS(read)(void);
uint8_t  LED_CLASS(write)(uint8_t status);

如果我写另外一个驱动，也是一样有open，close，read，write接口，假设是个FLASH设备。
那还是一样的：

#define  FLASH_CLASS(x) flash_device_ ## x
void     FLASH_CLASS(open)(void);
void     FLASH_CLASS(close)(void);
uint8_t  FLASH_CLASS(read)(void);
uint8_t  FLASH_CLASS(write)(uint8_t status);

看起来舒服多了！Good!
那么##和#又有什么区别呢？
##刚刚已经说了，是黏贴字符串
而#表示的是将参数转换为字符串
下面写一个跟#相关的例子:

#include 

#define Print(x) printf("%s %d\n",#x,x);
int main(void)
{
	Print(100);
	return 0 ;	
} 

运行结果: