int main( int argc, char * * argv)
{
    unsigned int i,fd,fd1;
    int res, ret;
       unsigned char buf[64]={   } ;  
    int bytes_to_copy=0;
    int filesize=0;
    int buf_size = sizeof(buf) ;
    struct stat attribute;
    unsigned char tpm_sha1start[ ] = { 0, TPM_TAG_RQU_COMMAND,
                0, 0, 0, 10,
                0, 0, 0, TPM_ORD_SHA1Start};   //   在模拟tpm下用到的  
    unsigned char tpm_sha1update[ ]={0,TPM_TAG_RQU_COMMAND,
               0,0,0,22,
              0,0,0,TPM_ORD_SHA1Update,
              0,0,0,64,
           buf[0], buf[1], buf[2], buf[3], buf[4], buf[5], buf[6], buf[7], buf[8], buf[9],
           buf[10], buf[11], buf[12], buf[13], buf[14], buf[15], buf[16], buf[17], buf[18],
buf[19],buf[20], buf[21], buf[22], buf[23], buf[24], buf[25], buf[26], buf[27], buf[28],
buf[29],  buf[30], buf[31], buf[32], buf[33],buf[34],buf[35],buf[36],buf[37],buf[38],
buf[39],buf[40],buf[41],buf[42],buf[43],buf[44],buf[45],buf[46],buf[47],buf[48],buf[49],
buf[50],buf[51],buf[52],buf[53],buf[54],buf[55],buf[56],buf[57],buf[58],buf[59],buf[60],
buf[61],buf[62],buf[63]};  //   在模拟tpm下用到的

fd = open ( "/dev/tpm" , O_RDWR) ;
    if ( fd < 0) {
        printf ( "Error: Open() failed: (%04x)\n " , fd) ;
        return - 1;
        }     

fd1=open("hello.txt",O_RDWR);
    if (fd1 < 0)
    {
    printf("Error opening file\n");
    return -1;
    }
    stat("hello.txt",&attribute);
    filesize = attribute.st_size;

    bytes_to_copy=filesize;
    printf("%d\n",bytes_to_copy);

    while (bytes_to_copy > 64)
        {
             read(fd1,buf,64);
       for(i=0;i<64;i++)
      printf("%c",buf[i]);
      printf("\n");  //打印buf中内容

    printf ( "sizeof(tpm_sha1update): %d\n" , sizeof (tpm_sha1update)) ;
    printf ( "data in tpm_sha1update: " ) ;
       for ( i = 0; i < sizeof ( tpm_sha1update) ; i++ )
                printf ( "%02x" , tpm_sha1update[i] ) ;
       printf ( "\n" ) ;   //打印tpm_sha1update中的内容

为什么第一次打印buf中的内容与下面打印tpm_sha1update中的内容不一样啊
第一次打印的内容确实是从文件中读出的内容而下面打印出来的buf的内容还是buf初始化时的内容
多谢高手指点了
中间代码有省略的.....