bswap_16, bswap_32, bswap_64 - reverse order of bytes

#include <byteswap.h>

bswap_16(x);
bswap_32(x);
bswap_64(x);

These macros return a value in which the order of the bytes in their 2-, 4-, or 8-byte arguments is reversed.

These macros return the value of their argument with the bytes reversed.

The program below swaps the bytes of the 8-byte integer supplied as its command-line argument. The following shell session demonstrates the use of the program:

$ ./a.out 0x0123456789abcdef
0x123456789abcdef ==> 0xefcdab8967452301

Program source

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

int
main(int argc, char *argv[])
{
    uint64_t x;

    if (argc != 2) {
        fprintf(stderr, "Usage: %s <num>\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    x = strtoull(argv[1], NULL, 0);
    printf("%#" PRIx64 " ==> %#" PRIx64 "\n", x, bswap_64(x));

    exit(EXIT_SUCCESS);
}

byteorder(3), endian(3)