[SOLVED] Cannot find property setter for "Chars"

Cannot find property setter for "Chars"

I am trying to do the following expression, but I keep running into this exception, "Cannot find property setter for 'chars'."

Here is the expression:

xstr, str : string;
for i := 1 to length(str) do
begin
  if ((i mod 2)<>0) then
  begin
    xstr[i] := char(Ord(str[i]) xor $AA);  <<<<------ Exception Raised
  end
  else
  begin
    xstr[i] := char(Ord(str[i]) xor $55);  <<<<------ Exception Raised
  end;
end;

The value of "str" is passed into the encryption method.

This is part of an encryption method. What is the best way to do this?

Solution

System.String is an immutable class, meaning you cannot modify instances of it. .NET requires modifying string operations to create new instances of a string. For your purpose, it’s probably easiest and most efficient to create a char array of the modified characters and then construct a string from that.

In general, the System.Text.StringBuilder class offers a mutable string instance.

In fact, even if it weren’t for the immutability of strings, your code would fail because you didn’t allocate a string, so assignment to xstr[i] would yield in a buffer overflow exception. You need to do that when using an array of char.