寻求两个函数是什么？(10分)

1、指定一字符串在另一字符串中最先出现位置的函数并要求此函数有设置搜索的起点。
2、返回一个字符串，该字符串中指定的子字符串已被替换成另一子字符串。

pos
stringreplace

pos没有设置的搜索起点，如有，能写出格式吗？

Delphi7自带的函数
function PosEx(const SubStr, S: string; Offset: Cardinal = 1): Integer;
var
I,X: Integer;
Len, LenSubStr: Integer;
begin
if Offset = 1 then
Result := Pos(SubStr, S)
else
begin
I := Offset;
LenSubStr := Length(SubStr);
Len := Length(S) - LenSubStr + 1;
while I <= Len do
begin
if S = SubStr[1] then
begin
X := 1;
while (X < LenSubStr) and (S[I + X] = SubStr[X + 1]) do
Inc(X);
if (X = LenSubStr) then
begin
Result := I;
exit;
end;
end;
Inc(I);
end;
Result := 0;
end;
end;
Delphi自带的函数

function StringReplace(const S, OldPattern, NewPattern: string;
Flags: TReplaceFlags): string;
var
SearchStr, Patt, NewStr: string;
Offset: Integer;
begin
if rfIgnoreCase in Flags then
begin
SearchStr := AnsiUpperCase(S);
Patt := AnsiUpperCase(OldPattern);
end else
begin
SearchStr := S;
Patt := OldPattern;
end;
NewStr := S;
Result := '';
while SearchStr <> '' do
begin
Offset := AnsiPos(Patt, SearchStr);
if Offset = 0 then
begin
Result := Result + NewStr;
Break;
end;
Result := Result + Copy(NewStr, 1, Offset - 1) + NewPattern;
NewStr := Copy(NewStr, Offset + Length(OldPattern), MaxInt);
if not (rfReplaceAll in Flags) then
begin
Result := Result + NewStr;
Break;
end;
SearchStr := Copy(SearchStr, Offset + Length(Patt), MaxInt);
end;
end;

谢谢！