Rob, thank you for your complete and clear answer. --- In [email protected], Rob Kennedy <[EMAIL PROTECTED]> wrote: > > Roberto Freitas wrote: > > Hi, I supose it's something very easy, but I realy don't known how to > > do it. > > P is a PAnsiChar variable and S is a String variable. > > This sentence is fine: > > S := P; > > That allocates a new string S and copies the memory pointed to by P into > that string. > > > But the inverse sentence is not: > > P := S; > > (I get a compiler error message: Incompatible types: 'String' > > and 'PAnsiChar') > > PAnsiChar is a pointer to an AnsiChar. The compiler doesn't know which > AnsiChar you want P to point at. > > One way to do what you want is P := PAnsiChar(S). That makes P point to > the first character of S. If S is empty, then P will point to a null > character. Either way, P <> nil. > > Another way is to use the StrLCopy function. It will copy the contents > of S into the memory pointed to by P. To use that, P must already point > somewhere that you're allowed to change. (That is, it can't point to > read-only memory.) > > > So, I try another track. It's possible to do: > > P^ := '0'; > > That assigns the character 0 into the AnsiChar pointed to by P. The rest > of the memory block P points to remains unchanged. If P doesn't point > somewhere valid already, then you'll get a run-time error. > > Also valid is P := '0'. That assigns P to point to the 0 character, so > if P was pointing at something else already, that value is lost. > > > But it's not possible to do: > > for i := 1 to Length(S) do > > P^ := Copy(S, i, 1); > > First of all, if the third argument to Copy is 1, then Copy probably > isn't the function you should call anyway. That kind of syntax is seen > most often from people who've been using VB too long. To get a single > character form a string, use the bracket operator: S[i]. > > The Copy function always returns a string, so your code fails for the > same reason P := S failed. > > > Conclusion: I need to append S to P but I don't known how to do it. > > Can somebody help me? > > To append, you need to get to the end P. You can use the StrEnd function > for that. It returns a PChar. Then use StrLCopy to copy S into that. The > more direct function is StrLCat, which concatenates two PChars. In > either case, you must be absolutely certain that the destination pointer > points to a block of memory large enough to hold both strings. Delphi > can't check that for PChars the way it can for strings. > > -- > Rob >
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