I have a c program below, I would like to send out a 32 bit message in a particular order Eg.0x00000001.

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <stdint.h>

struct  test
{
    uint16_t a;
    uint16_t b;
};

int main(int argc, char const *argv[])
{
    char buf[4];
    struct test* ptr=(struct test*)buf;
    ptr->a=0x0000;
    ptr->b=0x0001;
    printf("%x %x\n",buf[0],buf[1]); //output is 0 0
    printf("%x %x\n",buf[2],buf[3]); //output is 1 0
    return 0;
}

Then I test it by print out the values in char array. I got output in the above comments. Shouldn't the output be 0 0 and 0 1? since but[3] is the last byte? Is there anything I missed?

Thanks!