i want to interface sd card with stm32f779bi part number of controller using sdio

i have got error in opening of file in f_open file

my f_mount returns with no error

i have done followin thing in my code 

if(f_mount(&SDFatFS,(TCHAR const*)SDPath, 0) == FR_OK)     //(TCHAR const*)SDPath

{

if(f_open(&SDFile, "STM32.TXT", FA_CREATE_ALWAYS | FA_WRITE) == FR_OK)

{

if(f_write(&SDFile, wtext, sizeof(wtext), (void *)&wbytes) == FR_OK)

{

f_close(&SDFile);

}

}

}

before this i have also link sd driver 

please reply me 

Thanks in advance