原文来自：http://blog.163.com/chenxiaofan_wy/blog/static/1648565882012281112084/
函数原型：
function StringReplace (const S, OldPattern, NewPattern: string; Flags: TReplaceFlags): string;
参数：
S：源字符串
OldPattern：待替换字符串
NewPattern：替换字符串
Flags：包含以下方式
rfReplaceAll：全部替换
rfIgnoreCase：忽略大小写
实例：
var
aStr: String;
begin
aStr := 'This is a book, not a pen!';
ShowMessage(StringReplace (aStr, 'a', 'two', []));//This is two book, not a pen!只替换了第一个符合的字
ShowMessage(StringReplace (aStr, 'a', 'two', [rfReplaceAll]));//This is two book, not two pen!替换了所有符合的字
aStr := 'This is a book, not A pen!';
ShowMessage(StringReplace (aStr, 'a', 'two', [rfReplaceAll]));//This is two book, not A pen!只替换了符合的字(小写a)
ShowMessage(StringReplace (aStr, 'a', 'two', [rfReplaceAll, rfIgnoreCase]));//This is two book, not two pen!不管大小写替换了所有符合的字
end;