Problem using the FloatToStrF() method

I get the following error:  [ bcc32 Error] MAINFORM.CPP(119): E2451 Undefined symbol 'sffFloat'  I have included the that the help file suggested, but I still get the same error.  Can anyone help me PLEASE?  Here is the code:

double f;

String str;

f = -1234.65; // The double assignment

str.FloatToStrF(f,sffFloat,10,2); // The offending line of code

//str.printf(L"$ %f",f); // This did not work either

ShowMessage(str); // A test of the String

Edit2->Text=str; // Ultimately what I wanted