Inno Setup FileCopy failing

问题

I'm working on an installer that needs to create a backup of a directory prior to installing. The method I implement is purely to copy all files from the current directory to a new directory and then I am free to overwrite files (my installer) in the old directory.

However, I receive a prompt indicating file copy failed, but I just cannot understand why it doesn't work. My error message prints the correct directory\filename and I can verify that they exist and aren't open in any external programs.

Below is the code, taken (and modified slightly) from: http://blogs.candoerz.com/question/139833/inno-setup-copy-folder-subfolders-and-files-recursively-in-code-section.aspx

function DirectoryCopy(SourcePath, DestPath: string): boolean;
  var
    FindRec: TFindRec;
    SourceFilePath: string;
    DestFilePath: string;
  begin
    if FindFirst(SourcePath + '\*', FindRec) then begin
      try
        repeat
          if (FindRec.Name <> '.') and (FindRec.Name <> '..') then begin
            SourceFilePath := SourcePath + '\' + FindRec.Name;
            DestFilePath := DestPath + '\' + FindRec.Name;
            if FindRec.Attributes and FILE_ATTRIBUTE_DIRECTORY = 0 then begin
              if FileCopy(SourceFilePath, DestFilePath, False) then begin
                Result := True;
                MsgBox('Copy Worked!', mbInformation, MB_OK);
              end else begin
                Result := False;
                MsgBox('Copy Failed!'+SourceFilePath, mbInformation, MB_OK);
              end;
            end else begin
              if CreateDir(DestFilePath) then begin
                Result := True;
                MsgBox('Created Dir!', mbInformation, MB_OK);
                DirectoryCopy(SourceFilePath, DestFilePath);
              end else begin
                Result := False;
                MsgBox('Failed to create Dir!', mbInformation, MB_OK);
              end;
            end;
          end;
        until not FindNext(FindRec);
      finally
        FindClose(FindRec);
      end;
    end else begin
      Result := False;
      MsgBox('Failed to List!', mbInformation, MB_OK);
    end;
  end;

回答1:

I suspect that the directory you are trying to copy to doesn't exist. You need to create the directory first using CreateDir or ForceDirectories. The file functions (including Martin's DirectoryCopy function, which uses these internal functions) require the directory to exist or they will fail. They will not automatically create the path for you. It is a pity this isn't documented anywhere (that I could find, although someone may be able to correct me on that) as it caught me out for a while too.

The original link to Martin's DirectoryCopy function is available here.

回答2:

As we didn't receive any information that can be used for debugging your actual problem, I'm posting generic instructions for debugging problems with files.

To find out why any (file) system function fails, use the GetLastError WinAPI function. You can also use the SysErrorMessage support function to convert an error code to a message. The function is a wrapper for the FormatMessage WinAPI function.

function GetLastError: Cardinal;
  external 'GetLastError@kernel32.dll stdcall';

function FileCopyLogged(ExistingFile, NewFile: String; FailIfExists: Boolean): Boolean;
var
  Error: Cardinal;
begin
  Result := FileCopy(ExistingFile, NewFile, FailIfExists);

  if not Result then
  begin
    Error := GetLastError;
    Log(
      Format(
        'Copying "%s" to "%s" failed with code %d (0x%x) - %s', [
        ExistingFile, NewFile, Error, Error, SysErrorMessage(Error)]));
  end
    else
  begin
    Log(Format('Copying "%s" to "%s" succeeded', [ExistingFile, NewFile]));
  end;
end;

---

A correct call to the FileCopy (or the FileCopyLogged) is like:

FileCopyLogged(
  ExpandConstant('{app}\MyProg.exe'), 
  ExpandConstant('{app}\archive\MyProg.exe'),
  False);

---

As @RobertWigley already posted in his answer, make sure the target folder exists. If it does not, you will get error code 3 (The system cannot find the path specified).

Also make sure you use a full path to a target file in the NewFile argument (C:\folder\file). Not just a path to a target folder (C:\folder or C:\folder\). If you use just a path to the target folder, you will get error code 5 (Access is denied).

Of course both these codes can indicate other problems too.

来源：https://stackoverflow.com/questions/39535942/inno-setup-filecopy-failing