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

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#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)

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

tmp register

A very good way to control temperarily used memory.

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#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)
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