Examples of errors detected by the V567 diagnostic

V567. The modification of a variable is unsequenced relative to another operation on the same variable. This may lead to undefined behavior.

Fennec Media

V567 Undefined behavior. The 'm_nCurrentBitIndex' variable is modified while being used twice at single sequence point. MACLib unbitarrayold.cpp 78

uint32 CUnBitArrayOld::DecodeValueRiceUnsigned(uint32 k)
{
  ....
  while (!(m_pBitArray[m_nCurrentBitIndex >> 5] &
     Powers_of_Two_Reversed[m_nCurrentBitIndex++ & 31])) {}
  ....
}

SAGA GIS

V567 Undefined behavior. The 'iFloater' variable is modified while being used twice between sequence points. shapes_lines line_simplification.cpp 248

bool CLine_Simplification::Simplify(
  CSG_Shape *pLine, int iPart, bool *Keep)
{
  ....
  Keep[iFloater--] = iAnchor == 0 && iFloater ==
    pLine->Get_Point_Count(iPart) - 1;
  ....
}

Miranda IM

V567 Undefined behavior. The 's' variable is modified while being used twice between sequence points. msn ezxml.c 371

short ezxml_internal_dtd(ezxml_root_t root, char *s,
  size_t len)
{
  ....
  while (*(n = ++s + strspn(s, EZXML_WS)) && *n != '>') {
  ....
}

It's not guaranteed that 's' will be incremented before calling the strspn function.

IPP Samples

V567 Undefined behavior. The 'pTemp' variable is modified while being used twice between sequence points. me umc_me_cost_func.h 168

template<typename T, Ipp32s size> void HadamardFwdFast(
  ...., Ipp16s* pDst)
{
  Ipp32s *pTemp;
  ....
  for(j=0;j<4;j++) {
    a[0] = pTemp[0*4] + pTemp[1*4];
    a[1] = pTemp[0*4] - pTemp[1*4];
    a[2] = pTemp[2*4] + pTemp[3*4];
    a[3] = pTemp[2*4] - pTemp[3*4];
    pTemp = pTemp++;

    pDst[0*4] = (Ipp16s)(a[0] + a[2]);
    pDst[1*4] = (Ipp16s)(a[1] + a[3]);
    pDst[2*4] = (Ipp16s)(a[0] - a[2]);
    pDst[3*4] = (Ipp16s)(a[1] - a[3]);
    pDst = pDst++;
  }
  ....
}

Typical Undefined behavior!

Similar errors can be found in some other places:

• V567 Undefined behavior. The 'pDst' variable is modified while being used twice between sequence points. me umc_me_cost_func.h 174
• V567 Undefined behavior. The 'pTemp' variable is modified while being used twice between sequence points. me umc_me_cost_func.h 219
• V567 Undefined behavior. The 'pDst' variable is modified while being used twice between sequence points. me umc_me_cost_func.h 238

IPP Samples

V567 Undefined behavior. The 'm_curIndex' variable is modified while being used twice between sequence points. vc1_enc umc_vc1_enc_planes.h 630

bool MoveOnNextFrame()
{
  if (m_nFrames>0)
  {
    m_pFrame[m_curIndex] = 0;
    m_curIndex = (++m_curIndex)%m_maxN;
    m_nFrames--;
    return true;
  }
  return false;
}

IPP Samples

V567 Undefined behavior. The 'm_Quant.LimIQuant' variable is modified while being used twice between sequence points. vc1_enc umc_vc1_enc_brc_gop.cpp 241

void VC1BRC_I::CompleteFrame(ePType picType)
{
  ....
  m_Quant.LimIQuant = m_Quant.LimIQuant--;
  ....
  m_Quant.IQuant = m_Quant.IQuant--;
  ....
}

Similar errors can be found in some other places:

• V567 Undefined behavior. The 'm_Quant.IQuant' variable is modified while being used twice between sequence points. vc1_enc umc_vc1_enc_brc_gop.cpp 243

Doom 3

V567 Undefined behavior. The 'dir_cache_index' variable is modified while being used twice between sequence points. TypeInfo filesystem.cpp 1877

int idFileSystemLocal::ListOSFiles(....)
{
  ....
  dir_cache_index = (++dir_cache_index) % MAX_CACHED_DIRS;
  ....
}

This is what should have been written here: dir_cache_index = (dir_cache_index + 1) % MAX_CACHED_DIRS;

ffdshow

V567 Undefined behavior. The 'm_Offset' variable is modified while being used twice between sequence points. quicksyncutils.h 257

inline bool PopFront(T& res, DWORD dwMiliSecs)
{
  ....
  m_Offset = ++m_Offset % m_Capacity;
  ....
}

Network Security Services (NSS)

V567 Undefined behavior. The 'j' variable is modified while being used twice between sequence points. pk11slot.c 1926

PK11SlotList *
PK11_GetAllTokens(....)
{
  ....
  int j = 0;
  PRInt32 waste[16];
  ....
#if defined( XP_WIN32 )
  /* This is works around some horrible cache/page thrashing
  ** problems on Win32.  Without this, this loop can take up to
  ** 6 seconds at 100% CPU on a Pentium-Pro 200.  The thing this
  ** changes is to increase the size of the stack frame and
  ** modify it. Moving the loop code itself seems to have no
  ** effect. Dunno why this combination makes a difference,
  ** but it does.
  */
  waste[j & 0xf] = j++;
#endif
  ....
}

AssaultCube Reloaded

V567 Undefined behavior. The 'fullconsole' variable is modified while being used twice between sequence points. console.h 12

template<class LINE> struct consolebuffer
{
  void toggleconsole()
  {
    extern int altconsize;
    if(!fullconsole) fullconsole = altconsize ? 1 : 2;
    else fullconsole = ++fullconsole % 3;
  }
  ....
};

Snes9x

V567 Undefined behavior. The 'outputOffset' variable is modified while being used twice between sequence points. memmap.cpp 3926

static bool8 ReadBPSPatch (Stream *r, long, int32 &rom_size)
{
  ....
  while(length--)
    patched_rom[outputOffset++] = Memory.ROM[outputOffset];
  ....
}

Source Engine SDK

V567 Undefined behavior. The 'm_nNewSequenceParity' variable is modified while being used twice between sequence points. Client (HL2) c_baseanimating.cpp 5301

int m_nNewSequenceParity;
int m_nResetEventsParity;

void C_BaseAnimating::ResetSequenceInfo( void )
{
  ....
  m_nNewSequenceParity =
    ( ++m_nNewSequenceParity ) & EF_PARITY_MASK;
  m_nResetEventsParity =
    ( ++m_nResetEventsParity ) & EF_PARITY_MASK;
  ....
}

Similar errors can be found in some other places:

• V567 Undefined behavior. The 'm_nResetEventsParity' variable is modified while being used twice between sequence points. Client (HL2) c_baseanimating.cpp 5302

Rhino (JavaScript engine)

V567 Undefined behavior. The 'currentMap' variable is modified while being used twice between sequence points. aossessionmanager.cpp 140

u4 AOSSessionManager::threadprocSessionManager(AThread& thread)
{
  ....
  currentMap = ((++currentMap) % pThis->m_HolderSize);
  ....
}

Steamworks SDK

V567 Undefined behavior. The 'm_nCurrentLeaderboard' variable is modified while being used twice between sequence points. leaderboards.cpp 201

int m_nCurrentLeaderboard;

void CLeaderboards::OnMenuSelection(....)
{
  ....
  m_nCurrentLeaderboard = ++m_nCurrentLeaderboard % 2;
  ....
}

CryEngine 3 SDK

V567 Undefined behavior. The 'm_index' variable is modified while being used twice between sequence points. inetwork.h 2303

void AddSample( T x )
{
  m_index = ++m_index % N;
  ....
}

Scilab

V567 Undefined behavior. The 's' variable is modified while being used twice between sequence points. ezxml.c 385

short ezxml_internal_dtd(ezxml_root_t root, char *s, size_t len)
{
  ....
  while (*(n = ++s + strspn(s, EZXML_WS)) && *n != '>') {
  ....
}

Scilab

V567 Undefined behavior. The 'i' variable is modified while being used twice between sequence points. csvread.c 620

static char **replaceStrings(....)
{
  ....
  int i = 0;
  ....
  for (i = 0; i < nr; i = i++)
  ....
}

Word for Windows 1.1a

V567 Undefined behavior. The 'iBitmap' variable is modified while being used twice between sequence points. ddedit.c 107

CmdBitmap()
{
  static int  iBitmap = 0;
  ....
  iBitmap = ++iBitmap % MAXBITMAP;
}

Similar errors can be found in some other places:

• V567 Undefined behavior. The 'iIcon' variable is modified while being used twice between sequence points. ddedit.c 132
• V567 Undefined behavior. The 'iCursor' variable is modified while being used twice between sequence points. ddedit.c 150

Tesseract

V567 Undefined behavior. The 'num_deleted_boxes' variable is modified while being used twice between sequence points. libtesseract303 tabvector.cpp 735

void TabVector::Evaluate(....) {
  ....
  int num_deleted_boxes = 0;
  ....
  ++num_deleted_boxes = true;
  ....
}

Chromium

V567 Undefined behavior. The 'g_color_index' variable is modified while being used twice between sequence points. window_type_launcher.cc 60

int g_color_index = 0;

explicit ModalWindow(ui::ModalType modal_type) : ....
{
  ++g_color_index %= arraysize(g_colors);
  ....
}

Similar errors can be found in some other places:

• V567 Undefined behavior. The 'g_color_index' variable is modified while being used twice between sequence points. window_type_launcher.cc 123

VNL

V567 Undefined behavior. The 'mz_array_position' variable is modified while being used twice between sequence points. vnl_random.cxx 174

unsigned long vnl_random::lrand32()
{
  ....
  mz_array_position = (++mz_array_position) %
                      vnl_random_array_size;
  return p2;
}

Oracle VM Virtual Box

V567 Undefined behavior. The 'curg' variable is modified while being used twice between sequence points. consoleevents.h 75

template<class C> class ConsoleEventBuffer
{
public:
  ....
  C get()
  {
    C c;
    if (full || curg != curp)
    {
      c = buf[curg];
      ++curg %= sz;             // <=
      full = false;
    }
    return c;
  }
....
};

Similar errors can be found in some other places:

• V567 Undefined behavior. The 'curp' variable is modified while being used twice between sequence points. consoleevents.h 95
• V567 Undefined behavior. The 'curp' variable is modified while being used twice between sequence points. consoleevents.h 122

Miranda NG

V567 Undefined behavior. The 'i' variable is modified while being used twice between sequence points. Facebook connection.cpp 191

void FacebookProto::UpdateLoop(void *)
{
  ....
  for (int i = -1; !isOffline(); i = ++i % 50)
  ....
}

Similar errors can be found in some other places:

• V567 Undefined behavior. The order of argument evaluation is not defined for 'mir_snwprintf' function. The 'timeout' variable is modified while being used twice between sequence points. WhenWasIt dlg_handlers.cpp 883

Godot Engine

V567 Undefined behavior. The 'selected_track' variable is modified while being used twice between sequence points. animation_editor.cpp 1378

void AnimationKeyEditor::_track_editor_input_event(....)
{
  ....
  if (v_scroll->is_visible() && p_input.is_action("ui_page_up"))
    selected_track=selected_track--;;
  ....
}

Godot Engine

V567 Undefined behavior. The 't' variable is modified while being used twice between sequence points. tween_interpolaters.cpp 265

static real_t out(real_t t, real_t b, real_t c, real_t d)
{
  return c * ((t = t / d - 1) * t * t + 1) + b;
}

Similar errors can be found in some other places:

• V567 Undefined behavior. The 't' variable is modified while being used twice between sequence points. tween_interpolaters.cpp 271
• V567 Undefined behavior. The 't' variable is modified while being used twice between sequence points. tween_interpolaters.cpp 367

Unreal Engine 4

V567 Undefined behavior. The 'NextSampleIndex' variable is modified while being used twice between sequence points. performancemonitor.h 77

void Tick(double CurrentTime, float Value)
{
  ....
  NextSampleIndex = ++NextSampleIndex % SampleSize;
  ....
}

Apple II emulator

V567 Undefined behavior. The 'addr' variable is modified while being used twice between sequence points. cpu.cpp 564

void CpuSetupBenchmark ()
{
  ....
  *(mem+addr++) =
      (opcode >= BENCHOPCODES) ? 0x00 : ((addr >> 4)+1) << 4;
  ....
}

Gamer_Z eXtreme Party

V567 Undefined behavior. The 'readOffset' variable is modified while being used twice between sequence points. bitstream.h 952

template <>
  inline bool BitStream::Read(bool &var)
{
  if ( readOffset + 1 > numberOfBitsUsed )
    return false;

  if (data[ readOffset >> 3 ] & ( 0x80 >> ( readOffset++ % 8 ) ))
    var = true;
  else
    var = false;

  return true;
}

Similar errors can be found in some other places:

• V567 Undefined behavior. The 'bitStream->readOffset' variable is modified while being used twice between sequence points. bitstream.cpp 194
• V567 Undefined behavior. The 'bitStream->readOffset' variable is modified while being used twice between sequence points. bitstream.cpp 208

FreeSWITCH

V567 Unspecified behavior. The order of argument evaluation is not defined for 'strtol' function. Consider inspecting the 'exp' variable. switch_utils.c 3759

SWITCH_DECLARE(int) switch_number_cmp(const char *exp, int val)
{
  for (;; ++exp) {
    int a = strtol(exp, (char **)&exp, 10);
    if (*exp != '-') {
      if (a == val)
        return 1;
    } else {
      int b = strtol(++exp, (char **)&exp, 10);        // <=
      ....
    }
    if (*exp != ',')
      return 0;
  }
}

CryEngine V

V567 Undefined behavior. The 'm_current' variable is modified while being used twice between sequence points. operatorqueue.cpp 105

bool COperatorQueue::Prepare(....)
{
  ++m_current &= 1;
  m_ops[m_current].clear();
  return true;
}

Similar errors can be found in some other places:

• V567 Undefined behavior. The 'itail' variable is modified while being used twice between sequence points. trimesh.cpp 3101
• V567 Undefined behavior. The 'ihead' variable is modified while being used twice between sequence points. trimesh.cpp 3108
• V567 Undefined behavior. The 'ivtx' variable is modified while being used twice between sequence points. boolean3d.cpp 1194
• And 5 additional diagnostic messages.

CMaNGOS

V567 Undefined behavior. The 'm_uiMovePoint' variable is modified while being used twice between sequence points. boss_onyxia.cpp 405

void UpdateAI(const uint32 uiDiff) override
{
  ....
  switch (urand(0, 2))
  {
    case 0:
      ....
    case 1:
    {
        // C++ is stupid, so add -1 with +7
        m_uiMovePoint += NUM_MOVE_POINT - 1;
        m_uiMovePoint %= NUM_MOVE_POINT;
        break;
    }
    case 2:
        ++m_uiMovePoint %= NUM_MOVE_POINT; // <=
        break;
  }
  ....
}

Similar errors can be found in some other places:

• V567 Undefined behavior. The 'm_uiCrystalPosition' variable is modified while being used twice between sequence points. boss_ossirian.cpp 150

Far2l

V567 Undefined behavior. The 'Item[FocusPos]->Selected' variable is modified while being used twice between sequence points. dialog.cpp 3827

int Dialog::Do_ProcessSpace()
{
  ....
  if (Item[FocusPos]->Flags&DIF_3STATE)
    (++Item[FocusPos]->Selected)%=3;         // <=
  else
    Item[FocusPos]->Selected = !Item[FocusPos]->Selected;
  ....
}

Similar errors can be found in some other places:

• V567 Undefined behavior. The '::ViewerID' variable is modified while being used twice between sequence points. viewer.cpp 117

Steinberg SDKs

V567 Undefined behavior. The 'p' variable is modified while being used twice between sequence points. mdaAmbienceProcessor.cpp 151

void AmbienceProcessor::doProcessing (ProcessData& data)
{
  ....
  ++p  &= 1023;
  ++d1 &= 1023;
  ++d2 &= 1023;
  ++d3 &= 1023;
  ++d4 &= 1023;
  ....
}

ofPennerEasing

V567 CWE-758 The modification of the 't' variable is unsequenced relative to another operation on the same variable. This may lead to undefined behavior. easing_equations.cpp 201

static real_t in_out(real_t t, real_t b, real_t c, real_t d) {
  if ((t /= d / 2) < 1) return c / 2 * t * t * t + b;
  return c / 2 * ((t -= 2) * t * t + 2) + b;
}

Similar errors can be found in some other places:

• V567 CWE-758 The modification of the 't' variable is unsequenced relative to another operation on the same variable. This may lead to undefined behavior. easing_equations.cpp 274

LibreOffice

V567 The modification of the 'nCount' variable is unsequenced relative to another operation on the same variable. This may lead to undefined behavior. stgio.cxx 214

FatError EasyFat::Mark(....)
{
  if( nCount > 0 )
  {
    --nCount /= GetPageSize();
    nCount++;
  }
  ....
}

Doom 1

V567 [CWE-758] Undefined behavior. The 'eventhead' variable is modified while being used twice between sequence points. d_main.c 153

void D_PostEvent (event_t* ev)
{
  events[eventhead] = *ev;
  eventhead = (++eventhead)&(MAXEVENTS-1);
}

void D_ProcessEvents (void)
{
  ....
  for ( ; ....; eventtail = (++eventtail)&(MAXEVENTS-1) )
  {
    ....
  }
}

void CheckAbort (void)
{
  ....
  for ( ; ....; eventtail = (++eventtail)&(MAXEVENTS-1) )
  {
    ....
  }
}

Similar errors can be found in some other places:

• V567 [CWE-758] Undefined behavior. The 'eventtail' variable is modified while being used twice between sequence points. d_main.c 170
• V567 [CWE-758] Undefined behavior. The 'eventtail' variable is modified while being used twice between sequence points. d_net.c 464

glTF library

V567 The modification of the 'position.chars_read_current_line' variable is unsequenced relative to another operation on the same variable. This may lead to undefined behavior. json.hpp 3832

struct position_t
{
  ....
  std::size_t chars_read_current_line = 0;
  ....
};

std::char_traits<char>::int_type get()
{
  ++position.chars_read_total;
  ++position.chars_read_current_line;
  ....
  if (current == '\n')
  {
    ++position.lines_read;
    ++position.chars_read_current_line = 0;  // <=
  }
  return current;
}