Both. Delphi has two different sets of string manipulation functions, one
for null-terminated strings, and one for Pascal-type (I.E. length byte)
strings. You will find yourself stumbling across this distinction from time
to time. Mostly, there are Delphi functions that wrap around the most
common Windows API functions; for example, MessageBox, which is a Windows
API call, requires a PChar; but Delphi also has MessageDlg, which accepts
Pascal-type strings.
If you have text in a Pascal string and you want to pass it to a function
that expects a PChar, the following code is a "quick and dirty" way of
doing it, assuming that s is of type string and that the string has room
for one more character:
s[length(s)+1] := #0; { Appends a null to the end of the string }
C_Style_Function(@s[1]); { @s[1] is a PChar to the beginning of s }