FindfirstEx using recursion - delphi

Question

It drives me nuts (I'll should learn about recursion though)
But I'll can't make it work, something I'm doing wrong.
I was trying to make an exact copy of the FindFirst code below just with FindFirstEx but on the recursion I'll got stackoverflow and a lot of strange things happen so I'll guess that must be the wrong way using it so I'll removed it and replace it with the comment I'm stuck here...
So basically I'll need a procedure where I'm able to specify a directory and a file mask thats it.
procedure FetchFilesAndFolders(aPath, AMask; lbSearchResult: TMemo);
const
Find_First_Ex_Large_Fetch = 2;
var
hFile: Cardinal;
searchResult: Win32_Find_DataW;
begin
lbSearchResults.Lines.BeginUpdate;
hFile := FindFirstFileEx(PChar(aPath + aMask), FindExInfoStandard, #searchResult,
FindExSearchNameMatch, nil, Find_First_Ex_Large_Fetch);
If (hFile <> INVALID_HANDLE_VALUE) Then
begin
try
repeat
If (searchResult.dwFileAttributes And faDirectory = faDirectory) Then
begin
lbSearchResult.Lines.Append(IncludeTrailingBackSlash(aPath) +
string(searchResult.cFileName));
end
else
begin
// I'm stuck here...
end;
until (not FindNextFile(hFile, searchResult))
finally Winapi.Windows.FindClose(hFile);;
lbSearchResult.Lines.EndUpdate;
end;
Something like this but with FindFirstFileEx instead:
procedure FileSearch(const dirName, aMask: string; lbSearchResult:
TMemo);
var
searchResult: TSearchRec;
begin
lbSearchResult.Lines.BeginUpdate;
if FindFirst(dirName+ aMask, faAnyFile, searchResult) = 0 then
begin
try
repeat
if (searchResult.Attr and faDirectory) = 0 then
begin
lbSearchResult.Lines.Append(IncludeTrailingBackSlash(dirName) +
searchResult.Name);
end
else if (searchResult.Name <> '.') and (searchResult.Name <> '..') then
begin
FileSearch(IncludeTrailingBackSlash(dirName) + searchResult.Name,
lbSearchResult);
end;
until FindNext(searchResult) <> 0 finally FindClose(searchResult);
lbSearchResult.Lines.EndUpdate;
end;
end;
end;
So I'll need someone to show me doing it right.
Thank you!
Version 3 (still not working but no exception):
procedure FileSearch(const aPath, aMask: string; lbSearchResult: TMemo);
const
Find_First_Ex_Large_Fetch = 2;
var
hFile: Cardinal;
searchResult: Win32_Find_DataW;
begin
lbSearchResult.Lines.BeginUpdate;
hFile := FindFirstFileEx(PChar(aPath + aMask), FindExInfoStandard,
#searchResult, FindExSearchNameMatch, nil, Find_First_Ex_Large_Fetch);
If (hFile <> INVALID_HANDLE_VALUE) Then
begin
try
repeat
If (0 = (searchResult.dwFileAttributes and FILE_ATTRIBUTE_DIRECTORY)) then
begin
lbSearchResult.Lines.Add(IncludeTrailingBackSlash(aPath) +
string(searchResult.cFileName));
end
else
begin
If (searchResult.cFileName <> String('.')) And
(searchResult.cFileName <> '..') Then
lbSearchResult.Lines.Add(IncludeTrailingBackSlash(aPath) +
string(searchResult.cFileName));
// the following is not good, infinite!!!
// FileSearch(aPath, aMask, lbSearchResult);
end;
until (not FindNextFile(hFile, searchResult))
finally Winapi.Windows.FindClose(hFile);;
lbSearchResult.Lines.EndUpdate;
end;
end;
end;
All files and folders are shown which are inside the test folder but not any deeper so no recursion...
FileSearch('D:\projects\Test\', '*.*', Memo1);
So for example:
D:\projects\Test\Blubb
is shown but not the files inside or any directories from Test\Blubb\

Answer 1

The cause of your infinite recursion appears to be that you are omitting the test for the files '.' and '..'.
in the second code there is the line
else if (searchResult.Name <> '.') and (searchResult.Name <> '..') then
These two values are special directories that mean 'current directory' and 'parent directory' respectively. So while analysing the current directory it will find a 'subdirectory' called '.', which is actually a pointer to the directory that you are currently analysing. Therefore a recursive call to this subdirectory will analyse the same directory again, during which it will again find the directory '.' and again attempt to analyse the same directory, and so on for ever.
A similar situation arises for '..' which would analyse the parent directory.
It is critical that this test not be omitted.
Note on your version 3
One of my pet hates is not including begin...end blocks in if statements, and your 3rd version seems to illustrate why. You still get the infinite loop because your if statement does not apply to the recursion - which is exactly where it must apply.
The second, more serious issue is that the parameters of the recursive call are exactly the same as the original call. I can think of no circumstances where it is ever valid to do that (although I am sure that someone will correct me). Instead you must call with the name of the child directory. I have added a new variable fNewPath to simplify things.
procedure FileSearch(const aPath, aMask: string; lbSearchResult: TMemo);
const
Find_First_Ex_Large_Fetch = 2;
var
hFile: Cardinal;
searchResult: Win32_Find_DataW;
fNewPath : string;
begin
lbSearchResult.Lines.BeginUpdate;
hFile := FindFirstFileEx(PChar(aPath + aMask), FindExInfoStandard,
#searchResult, FindExSearchNameMatch, nil, Find_First_Ex_Large_Fetch);
If (hFile <> INVALID_HANDLE_VALUE) Then
begin
try
repeat
If (0 = (searchResult.dwFileAttributes and FILE_ATTRIBUTE_DIRECTORY)) then
begin
lbSearchResult.Lines.Add(IncludeTrailingBackSlash(aPath) +
string(searchResult.cFileName));
end
else
begin
If (searchResult.cFileName <> String('.')) And
(searchResult.cFileName <> '..') Then
begin // <-------------------
fNewPath := IncludeTrailingBackSlash(aPath) +
string(searchResult.cFileName);
lbSearchResult.Lines.Add( fNewPath );
FileSearch(fNewPath, aMask, lbSearchResult);
end; //<--------------- The recurstion *must* be covered by the if statement
end;
until (not FindNextFile(hFile, searchResult));
finally Winapi.Windows.FindClose(hFile);
lbSearchResult.Lines.EndUpdate;
end;
end;
end;