编译期字节序判断.cpp

编译期字节序判断.cpp

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

// C++ 11支持强类型枚举和constexpr
enum EndianOrder : uint32_t{
	ENDIAN_BIG			= 0x00010203,	/* 大端序 ABCD */
	ENDIAN_LITTLE		= 0x03020100,	/* 小端序 DCBA */
	ENDIAN_BIG_WORD		= 0x02030001,   /* 中端序 CDAB, Honeywell 316 风格 */
	ENDIAN_LITTLE_WORD	= 0x01000302	/* 中端序 BADC, PDP-11 风格 */
};

static constexpr uint8_t edvalx[4] = {0, 1, 2, 3};

union ED_TEST{
	constexpr ED_TEST(uint32_t val):x(val){}
		uint32_t x;
		uint8_t edval[4];// = {0, 1, 2, 3};
};

static constexpr ED_TEST m(0x00010203); //= {0x00010203};//{0x00,0x01,0x02,0x03};

constexpr EndianOrder getEndianOrder()
{
	return (EndianOrder)(*(uint32_t*)edvalx);
	// return (0x00 == m.edval[0])?
	// 	EndianOrder::ENDIAN_BIG:
	// 	(0x03 == m.edval[0])?
	// 	EndianOrder::ENDIAN_LITTLE:
	// 	(0x02 == m.edval[0])?
	// 	EndianOrder::ENDIAN_BIG_WORD:
	// 	EndianOrder::ENDIAN_LITTLE_WORD;

	//constexpr union{
	// 上面枚举中的四个值，在它们对应的字节序中
	// 值的内存布局应该与下面的edval一致
	//	uint8_t edval[4];// = {0, 1, 2, 3};
	//	uint32_t x;
	//}m;
	// switch(m.x){
	// 	case 0x00010203:return EndianOrder::ENDIAN_BIG;
	// 	case 0x03020100:return EndianOrder::ENDIAN_LITTLE;
	// 	case 0x02030001:return EndianOrder::ENDIAN_BIG_WORD;
	// 	case 0x01000302:return EndianOrder::ENDIAN_LITTLE_WORD;
	// }
	// return EndianOrder::ENDIAN_LITTLE;
	//return (EndianOrder)m.x;
}


int main()
{
// 这两个宏是gcc或者clang支持的
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
	puts("小端序");
#elif __BYTE_ORDER__== __ORDER_BIG_ENDIAN__
	puts("大端序");
#else
	puts("未知字节序");
#endif // __BYTE_ORDER__

	constexpr EndianOrder ed = getEndianOrder();
	static_assert(ed == EndianOrder::ENDIAN_BIG,"大端序");
	static_assert(ed == EndianOrder::ENDIAN_LITTLE,"小端序");
	static_assert(ed == EndianOrder::ENDIAN_BIG_WORD,"中大端序");
	static_assert(ed == EndianOrder::ENDIAN_LITTLE_WORD,"中小端序");

	return 0;
}