problem sd card

someone Know why this code not works? thanks.

     String call = "llamadauno";
     if (SD.exists(call))

mistake: no matching function for call to 'SDClass::exists(String&)'

The argument to exists() must be type char*, not String.

File names must be short 8.3 format. "llamadauno" is too long.

The maximum number of characters before the period is 8. and

btw the first two hits on google searching for "SD.exists(call) SDClass::exists(String&)"