static HINSTANCE kernelHandle;
bool (WINAPI *pGetDiskFreeSpaceEx)(LPCTSTR , ULARGE_INTEGER *,ULARGE_INTEGER *,
 ULARGE_INTEGER *);

//GetDiskFreeSpaceExのアドレスを取得する関数
int ModuleLoads()
{
    kernelHandle = LoadLibraryEx("KERNEL32.DLL", NULL, 0);
    if(kernelHandle == NULL){
        return(1);
    }else{
        pGetDiskFreeSpaceEx =
                (bool (WINAPI *)(LPCTSTR ,
                PULARGE_INTEGER, PULARGE_INTEGER, PULARGE_INTEGER))
                GetProcAddress(kernelHandle, "GetDiskFreeSpaceExA");
        if( pGetDiskFreeSpaceEx == NULL ){
            FreeLibrary( kernelHandle );
            kernelHandle = NULL;
            return(1);
        }
    }
    return(0);
}

void __fastcall TForm1::Button1Click(TObject *Sender)
{
        //64Bit UNSIGNED INTEGER
        ULARGE_INTEGER  UserFree;
        ULARGE_INTEGER  DiskTotal;
        ULARGE_INTEGER  DiskFree;

    //GetDiskFreeSpaceExをロードする
    if( ModuleLoads() ){
        ShowMessage( "Error ModuleLoads" );
        return;
    }

    if( pGetDiskFreeSpaceEx ){
        //ディスク容量を取得する
        pGetDiskFreeSpaceEx( "C:\\", &UserFree, &DiskTotal, &DiskFree );
        ShowMessage( Format("利用可能容量は%.2fGBです。",ARRAYOFCONST((
                    (((UserFree.QuadPart/1024.0)/1024.0)/1024.0)))) );
    }
    if( kernelHandle ) FreeLibrary( kernelHandle );
}