man3/bswap.3

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.TH BSWAP 3 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
bswap_16, bswap_32, bswap_64 \- reverse order of bytes
.SH SYNOPSIS
.nf
.B #include <byteswap.h>
.PP
.BI bswap_16( x );
.BI bswap_32( x );
.BI bswap_64( x );
.fi
.SH DESCRIPTION
These macros return a value in which the order of the bytes
in their 2-, 4-, or 8-byte arguments is reversed.
.SH RETURN VALUE
These macros return the value of their argument with the bytes reversed.
.SH ERRORS
These macros always succeed.
.SH CONFORMING TO
These macros are GNU extensions.
.SH EXAMPLE
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:
.PP
.in +4n
.EX
$ \fB./a.out 0x0123456789abcdef\fP
0x123456789abcdef ==> 0xefcdab8967452301
.EE
.in
.SS Program source
\&
.EX
#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 = strtoul(argv[1], NULL, 0);
    printf("0x%" PRIx64 " ==> 0x%" PRIx64 "\\n", x, bswap_64(x));

    exit(EXIT_SUCCESS);
}
.EE
.SH SEE ALSO
.BR byteorder (3),
.BR endian (3)