Wierd | 不常见的C语言写法

今天看到一种比较另类的C语言函数参数声明的写法, 编译居然能通过, 记录一下.

一种 C 语言参数声明写法

#include <stdio.h>

int main(argc, argv)
int argc;
char const *argv[];
{
	for (int i=0; i<argc; ++i) printf("%s%c", argv[i], i==argc-1?'\n':' ');
	return 0;
}

一种C语言Hello world的精简形式 (虽然会报出很多Warnings)

main(){printf("Hello, world!");}

tmp register

A very good way to control temperarily used memory.

#define UNUSED(x) ((void)(x))

#ifdef __cplusplus
  #define   __I     volatile             /*!< Defines 'read only' permissions */
#else
  #define   __I     volatile const       /*!< Defines 'read only' permissions */
#endif
#define     __O     volatile             /*!< Defines 'write only' permissions */
#define     __IO    volatile             /*!< Defines 'read / write' permissions */

#define __HAL_RCC_USART1_CLK_ENABLE()   do { \
                                        __IO uint32_t tmpreg = 0x00U; \
                                        SET_BIT(RCC->APB2ENR, RCC_APB2ENR_USART1EN);\
                                        /* Delay after an RCC peripheral clock enabling */ \
                                        tmpreg = READ_BIT(RCC->APB2ENR, RCC_APB2ENR_USART1EN);\
                                        UNUSED(tmpreg); \
                                          } while(0)