File system structure difference between cp and mv linux commands

[Indira ramasamy <vel.indira@xxxxxxxxx>]

Hi,

  I am facing one problem only with mv command not with cp command. I have a test program 

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mount.h>
#include <fcntl.h>
#include <errno.h>

int sync_file(char *file)
{
    FILE *fp=NULL;
    int fd;

    printf("file is %s\n",file);
    fp = fopen(file, "r");
    if(!fp)
        return -1;

    fd = fileno(fp);
    fflush(fp);
    fsync(fd);
    ioctl (fd, BLKFLSBUF, 0);
    fclose(fp);
    return 0;

}

int main()
{
    int len=0;
    FILE *fp = NULL;
    char buf[1024];
    char *fname = "/etc/test.conf";
    char fname_tmp[129] = "";


    len = sprintf(buf, "%s\n", "Newly added Line is there");

    snprintf(fname_tmp, 128, "%s.tmp", fname);

    if( (fp = fopen(fname_tmp,"a")) == NULL )
        printf(" ERROR: open(), error - %s\n",strerror(errno));

    fprintf(fp,"%s",buf);
    fflush(fp);

    fsync(fileno(fp));
    fclose(fp);
    system("cp -f /etc/test.conf.tmp /etc/test.conf");
   // system("mv -f /etc/test.conf.tmp /etc/test.conf");
    sync_file(fname);
    return 0;
}

Here i am opening a tmp file for writing. Then i am copying/moving for
original file. Then i do a fflush, fsync(), ioctl() to the original
file. Then i run this binary in linux machine(ext2 file system,
2.6.23.5 kernel) after that immediately  power off the machine. Then
power on machine, the file is disappeared or written data lost or file
gets corrupted if i move the tmp file to the original file. And there
is a no problem if i copy the tmp file to original file. So i want to
know the difference between the cp and mv command. Can you please give
me suggestion on it?

Thanks,
Indira.
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