From ReactOS

Windows Combo Box Structure

typedef struct _CBOX // Size: 0x4c
{
/* 000 */ PWND  spwnd;
/* 004 */ PWND  spwndParent;
/* 008 */ RECT  editrc;
/* 018 */ RECT  buttonrc;
/* 028 */ INT   cxCombo;
/* 02c */ INT   cyCombo;
/* 030 */ INT   cxDrop;
/* 034 */ INT   cyDrop;
/* 038 */ PWND  spwndEdit;
/* 03c */ PWND  spwndList;
/* 040 */ UINT  CBoxStyle:2;
/* 040 */ UINT  fFocus:1;
/* 040 */ UINT  fNoRedraw:1;
/* 040 */ UINT  fMouseDown:1;
/* 040 */ UINT  fButtonPressed:1;
/* 040 */ UINT  fLBoxVisible:1;
/* 040 */ UINT  OwnerDraw:2;
/* 040 */ UINT  fKeyboardSelInListBox:1;
/* 040 */ UINT  fExtendedUI:1;
/* 040 */ UINT  fCase:2;
/* 040 */ UINT  f3DCombo:1;
/* 040 */ UINT  fNoEdit:1;
/* 040 */ UINT  fRightAlign:1;
/* 040 */ UINT  fRtoLReading:1;
/* 044 */ HFONT hFont;
/* 048 */ LONG  styleSave;
} CBOX, *PCBOX;

// Window Extra data container.
typedef struct _WND2CBOX
{
  WND;
  PCBOX pCBox;
} WND2CBOX, *PWND2CBOX

References

• Windows Symbol files, userkdx.dll, !dso