重置PChar变量

Question

我对delphi win 32编程不太了解，但我希望有人能回答我的问题。

我将重复的l_sGetUniqueIdBuffer保存到数据库中，这是我想要避免的。

行之间的l_sGetUniqueIdBuffer实际上是不同的( l_sAuthorisationContent的值是xml，我可以看到调用getUniqueId生成了一个不同的值)。这个问题是间歇性的(重复的很少...)行之间的更新日期仅相差毫秒。

给定：

(不需要的代码被剪掉)

var
    l_sGetUniqueIdBuffer: PChar;
    FOutputBufferSize : integer;

begin
    FOutputBufferSize := 1024;
    ...
    while( not   dmAccomClaim.ADOQuClaimIdentification.Eof ) do
    begin

        // Get a unique id for the request
        l_sGetUniqueIdBuffer := AllocMem (FOutputBufferSize);

        l_returnCode := getUniqueId (m_APISessionId^, l_sGetUniqueIdBuffer, FOutputBufferSize);

        dmAccomClaim.ADOQuAddContent.Active := False;
        dmAccomClaim.ADOQuAddContent.Parameters.ParamByName('pContent').Value := (WideString(l_sAuthorisationContent));
        dmAccomClaim.ADOQuAddContent.Parameters.ParamByName('pClaimId').Value := dmAccomClaim.ADOQuClaimIdentification.FieldByName('SB_CLAIM_ID').AsString;
        dmAccomClaim.ADOQuAddContent.Parameters.ParamByName('pUniqueId').Value := string(l_sGetUniqueIdBuffer);
        dmAccomClaim.ADOQuAddContent.ExecSQL;

        FreeMem( l_sAuthorisationContent, l_iAuthoriseContentSize );

        FreeMem( l_sGetUniqueIdBuffer, FOutputBufferSize );
    end;
end;

我想我需要知道，l_sGetUniqueIdBuffer中的值是不是每一行都被重置了？

Answer 1

AllocMem的实现方式如下

function AllocMem(Size: Cardinal): Pointer;
begin
  GetMem(Result, Size);
  FillChar(Result^, Size, 0);
end;

所以，是的，l_sGetUniqueBuffer指向的值将始终重置为空字符串。

调试

var
    l_sGetUniqueIdBuffer: PChar;
    FOutputBufferSize : integer;
    list: TStringList;
begin
    FOutputBufferSize := 1024;
    ...

    list := TStringList.Create;
    try
      list.Sorted := True;
      while( not   dmAccomClaim.ADOQuClaimIdentification.Eof ) do
      begin

          // Get a unique id for the request
          l_sGetUniqueIdBuffer := AllocMem (FOutputBufferSize);

          l_returnCode := getUniqueId (m_APISessionId^, l_sGetUniqueIdBuffer, FOutputBufferSize);

          dmAccomClaim.ADOQuAddContent.Active := False;
          dmAccomClaim.ADOQuAddContent.Parameters.ParamByName('pContent').Value := (WideString(l_sAuthorisationContent));
          dmAccomClaim.ADOQuAddContent.Parameters.ParamByName('pClaimId').Value := dmAccomClaim.ADOQuClaimIdentification.FieldByName('SB_CLAIM_ID').AsString;
          dmAccomClaim.ADOQuAddContent.Parameters.ParamByName('pUniqueId').Value := string(l_sGetUniqueIdBuffer);

          if list.IndexOf(l_sGetUniqueIdBuffer) <> - 1 then
            write; //***** Place a breakpoint here.
          list.Add(l_sGetUniqueIdBuffer);

          dmAccomClaim.ADOQuAddContent.ExecSQL;

          FreeMem( l_sAuthorisationContent, l_iAuthoriseContentSize );

          FreeMem( l_sGetUniqueIdBuffer, FOutputBufferSize );
      end;
    finally
      list.Free;
    end;
end;