in file system

i want to write two buffers into the file i.e one buffer after another buffer.

i.e

char buff[100]={"tiva"};
char buff1[500]={"cseries");

iFResult = f_write(&g_sFileObject, buff, sizeof(buff) - 1,&ui32Byteswrite);

iFResult = f_write(&g_sFileObject, buff1, sizeof(buff1) - 1,&ui32Byteswrite);

but it is not working ,

i want the output i.e    tiva cseries

i try this program but it is not working..

do
{
//
// Read a block of data from the file. Read as much as can fit in the
// temporary buffer, including a space for the trailing null.
//
iFResult = f_write(&g_sFileObject,"tiva",6,&ui32Byteswrite);
iFResult = f_write(&g_sFileObject,"cseries",7,&ui32Byteswrite);
//
// If there was an error reading, then print a newline and return the
// error to the user.
//
if(iFResult != FR_OK)
{
UARTprintf("\n");
return((int)iFResult);
}

//
// Null terminate the last block that was read to make it a null
// terminated string that can be used with printf.
//
// buff[ui32Byteswrite] = 0;

//
// Print the last chunk of the file that was received.
//

}while(ui32Byteswrite ==13);