如何改进多个StringReplace调用？

Question

我从客户那里读取文件，我需要处理读取数据并删除一些不需要的字符。 我的功能有效，但我正在尝试改进FixData功能，以提高速度/性能和可维护性。

是否有可能用一些只会循环数据并用其需要的内容替换的东西替换多个StringReplace调用？

我找不到MultipleStringReplace或类似的功能。

MCVE：

function FixData(const vStr:string):string;
var i:integer;
begin
  Result:=vStr;

  // empty string
  if Result = #0 then Result := '';

  // fix just New line indicator
  if Result = #13#10 then  Result := #8;

  // remove 'end'/#0  characters
    if Pos(#0, Result) > 0 then
      for i := 1 to Length(Result) do
        if Result[i] = #0 then
          Result[i] := ' ';

    //  #$D#$A  -> #8
    if Pos(#$D#$A, Result) > 0 then
      Result := StringReplace(Result, #$D#$A, #8, [rfReplaceAll]);

    // remove &#xD
    if Pos('
', Result) > 0 then
      Result := StringReplace(Result, '
', '', [rfReplaceAll]);

    // #$A -> #8
    if Pos(#$A, Result) > 0 then
      Result := StringReplace(Result, #$A, #8, [rfReplaceAll]);

    // replace " with temp_replacement value
    if Pos(chr(34), Result) > 0 then
      Result := StringReplace(Result, chr(34), '\_/', [rfReplaceAll]);
end;

procedure TForm1.Button1Click(Sender: TObject);
var vStr,vFixedStr:string;
begin
  vStr:='testingmystr:"quotest" - '+#0+' substr 
 new line '#$A' 2nd line '#$D#$A' end of data';
  vFixedStr:=FixData(vStr);
end;

Answer 1

我猜，你必须将你的字符串拆分成一组字符串（非分隔符和分隔符（模式）），然后替换数组中的项目，然后再将它们组合起来。 你可以从较长的模式开始，然后选择更短的模式（对模式内部模式进行安全检查），然后额外的运行将是一个char-to-one-char替换（因为它们可以就地完成并且不需要内存复制）。

双重复制，搜索缩放为O（长度（输入）*计数（分隔符））。

像这样的伪代码草案（没有实现到最后一个点，只是为了让你有想法）：

由于您的模式很短，我认为线性搜索会没问题，否则会更加优化，但需要复杂的算法： https ： //en.wikipedia.org/wiki/String_searching_algorithm#Algorithms_using_a_finite_set_of_patterns

将其分类为您认为合适的小功能，以便于理解/维护。

Type TReplaceItem = record (match, subst: string; position: integer);
var matches: array of TReplaceItem;

SetLength(matches, 3);
matches[0].match := '
'; // most long first;
  matches[0].subst := ''; 
matches[1].match := #$D#$A; // most long first;
  matches[1].subst := #8; 
matches[2].match := #34; // most long first;
  matches[2].subst := '\_/'; 

sb := TStringBuilder.Create( 2*Length(InputString) ); 
// or TList<String>, or iJclStringList of Jedi CodeLib, or TStringList... depending on performance and preferences
// Capacity parameter is for - warming up, pre-allocating memory that is "usually enough" 
try    

  NextLetterToParse := 1;
  for I := Low(matches) to high(matches) do
    matches[I].position := PosEx(matches[I].match, InputString, NextLetterToParse ); 

  While True do begin

     ClosestMatchIdx := -1;

     ClosestMatchPos := { minimal match[???].Position that is >= NextLetterToParse };
     ClosestMatchIdx := {index - that very [???] above - of the minimum, IF ANY, or remains -1}

     if ClosestMatchIdx < 0 {we have no more matches} then begin

      //dump ALL the remaining not-yet-parsed rest
        SB.Append( Copy( InputString, NextLetterToParse , Length(InputString));

      // exit stage1: splitting loop
        break;
     end;

     // dumping the before-any-next-delimiter part of not-parsed-yet tail of the input
     // there may be none - delimiters could go one after another
     if ClosestMatchPos > NextLetterToParse then
         SB.Append( Copy( InputString, NextLetterToParse, ClosestMatchPos-NextLetterToParse);

     // dumping the instead-of-delimiter pattern
     SB.Append( matches[ ClosestMatchIdx ].Subst );

     ShiftLength := (ClosestMatchPos - NextLetterToParse) + Length(matches[ ClosestMatchIdx ].Match); 
     // that extra part got already dumped now

     Inc( NextLetterToParse, ShiftLength);

     for I := Low(matches) to high(matches) do
       if matches[I].position < NextLetterToParse then
          matches[I].position := PosEx(matches[I].match, InputString, NextLetterToParse ); 
     // updating next closest positions for every affected delimiter,
     // those that were a bit too far to be affected ( usually all 
     // but the one being dumped) need not to be re-scanned 

  end; // next stage 1 loop iteration

现在我们有一个容器/数组/列表/由非匹配块和替换模式组成的任何东西。 除了就地替换一个字符。 合并时间并进行最后一次扫描。

Stage2String := SB.ToString();

finally 
  SB.Destroy; 
end;

for I := 1 to Length( Stage2String ) do
  case Stage2String[I] of
    #0: Stage2String[I] := #32;

    #10, #13: Stage2String[I] := #8;
    // BTW - ^M=#13=#$D sometimes can be met without trailing ^J=#10=#$A
    // that was the end-of-line char used in old Macintosh text files

    else ; // do nothing, let it stay as is
  end;

Result := Stage2String;