C 宏定义来确定大端或小端机器? [英] C Macro definition to determine big endian or little endian machine?

问题描述

是否有单行宏定义来确定机器的字节顺序.我正在使用以下代码，但将其转换为宏会太长.

Is there a one line macro definition to determine the endianness of the machine. I am using the following code but converting it to macro would be too long.

unsigned char test_endian( void )
{
    int test_var = 1;
    unsigned char *test_endian = (unsigned char*)&test_var;

    return (test_endian[0] == 0);
}

推荐答案

支持任意字节顺序的代码，准备放入名为order32.h的文件中:

Code supporting arbitrary byte orders, ready to be put into a file called order32.h:

#ifndef ORDER32_H
#define ORDER32_H

#include <limits.h>
#include <stdint.h>

#if CHAR_BIT != 8
#error "unsupported char size"
#endif

enum
{
    O32_LITTLE_ENDIAN = 0x03020100ul,
    O32_BIG_ENDIAN = 0x00010203ul,
    O32_PDP_ENDIAN = 0x01000302ul,      /* DEC PDP-11 (aka ENDIAN_LITTLE_WORD) */
    O32_HONEYWELL_ENDIAN = 0x02030001ul /* Honeywell 316 (aka ENDIAN_BIG_WORD) */
};

static const union { unsigned char bytes[4]; uint32_t value; } o32_host_order =
    { { 0, 1, 2, 3 } };

#define O32_HOST_ORDER (o32_host_order.value)

#endif

您可以通过以下方式检查小端系统

You would check for little endian systems via

O32_HOST_ORDER == O32_LITTLE_ENDIAN

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