bswap_16, bswap_32, bswap_64

Standard C library (libc, -lc)

#include <byteswap.h>

uint16_t bswap_16(uint16_t x);
uint32_t bswap_32(uint32_t x);
uint64_t bswap_64(uint64_t x);

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

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

These functions always succeed.

GNU.

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

#include <byteswap.h>
#include <inttypes.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.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("%#w64x ==> %#w64x\n", x, bswap_64(x));
    exit(EXIT_SUCCESS);
}

byteorder(3), endian(3)