How to create a new folder in %APPDATA% using C++?

I've tried to include the IOUtils library and use the CSIDL command, but it isn't working...

Here is the part of the code that does it:

//------------------- Includes -----------------------
#include <fmx.h>
#include <IOUtils.hpp>
#pragma hdrstop

#include "Unit1.h"
#include "Unit2.h"
#include "Unit3.h"
//---------------------- end  ------------------------
//---- On Form Show (bugged event: It doesn't create the needed folder) ----

void __fastcall TfrmInicio::FormShow(TObject *Sender)
{
    if (TDirectory::Exists("CSIDL_APPDATA\\Nintersoft\\Ninterfin")) {
        if (FileExists("CSIDL_APPDATA\\Nintersoft\\Ninterfin\\Inf.nf")) {
            mmInfo->Lines->LoadFromFile("CSIDL_APPDATA\\Nintersoft\\Ninterfin\\Inf.nf");
        }
    }
    else {
            TDirectory::CreateDirectory("CSIDL_APPDATA\\Nintersoft\\Ninterfin");
    }
}

//--------------------------------- end ------------------------------------

I hope you can helpe me... Thanks a lot XD

You are not supposed to hard-code "CSIDL_APPDATA" itself directly into your directory path string. CSIDL_APPDATA is an ID number (specifically, 26) for a virtual folder that you have to resolve dynamically at runtime using the Win32 API, eg:

void __fastcall TfrmInicio::FormShow(TObject *Sender)
{
    WCHAR szPath[MAX_PATH+1] = {0};
    if (SUCCEEDED(SHGetFolderPathW(FmxHandleToHWND(Handle), CSIDL_APPDATA, NULL, SHGFP_TYPE_CURRENT, szPath)))
    {
        String DirPath = TPath::Combine(szPath, L"Nintersoft\\Ninterfin");
        TDirectory::CreateDirectory(DirPath);

        String FileName = TPath::Combine(DirPath, L"Inf.nf");
        if (TFile::Exists(FileName))
            mmInfo->Lines->LoadFromFile(FileName);
    }
}

Alternatively, on Vista and later only, use SHGetKnownFolderPath() instead:

void __fastcall TfrmInicio::FormShow(TObject *Sender)
{
    PWSTR pszPath;
    if (SUCCEEDED(SHGetKnownFolderPath(FOLDERID_RoamingAppData, 0, NULL, &pszPath)))
    { 
        String DirPath = TPath::Combine(pszPath, L"Nintersoft\\Ninterfin");
        CoTaskMemFree(pszPath);

        TDirectory::CreateDirectory(DirPath);

        String FileName = TPath::Combine(DirPath, L"Inf.nf");
        if (TFile::Exists(FileName))
            mmInfo->Lines->LoadFromFile(FileName);
    }
}

Alternatively, use Sysutils::GetEnvironmentVariable() to retrieve the value of %APPDATA% instead of using a CSIDL or KNOWNFOLDERID:

void __fastcall TfrmInicio::FormShow(TObject *Sender)
{
    String DirPath = TPath::Combine(Sysutils::GetEnvironmentVariable(L"APPDATA"), L"Nintersoft\\Ninterfin");
    TDirectory::CreateDirectory(DirPath);

    String FileName = TPath::Combine(DirPath, L"Inf.nf");
    if (TFile::Exists(FileName))
        mmInfo->Lines->LoadFromFile(FileName);
}