c - What is the proper use of DTM_GETIDEALSIZE? Treating the returned size as pixels gives me very large, sometimes variable, heights -

i'm trying autosize date-time picker controls dtm_getidealsize, don't quite how use message properly. while widths returned seem fine if treated pixels, heights seem not way off, change on time!

the sample program below creates 3 date-time pickers. first shows both date , time custom format, second shows dates dts_shortdatecenturyformat, , third shows times dts_timeformat. resizing window resizes 3 pickers using dtm_getidealsize. widths seem fine. however, heights of first 2 100, , height of last (the time picker) seems start @ 98 or , decreases 2 each resize until reaches 16, @ point stays @ 16.

this tested both windows vista , windows 7. error checking in below program inconsistent (but errors not checked purposes of keeping simple test example). however, note msdn explicitly documents dtm_getidealsize ever returning true no error condition specified.

thanks.

// 3 june 2015 #define unicode #define _unicode #define strict #define strict_typed_itemids #define cinterface #define winver 0x0600 #define _win32_winnt 0x0600 #define _win32_windows 0x0600 #define _win32_ie 0x0700 #define ntddi_version 0x06000000 #include <windows.h> #include <commctrl.h> #include <stdint.h> #include <uxtheme.h> #include <string.h> #include <wchar.h> #include <windowsx.h> #include <vsstyle.h> #include <vssym32.h> #include <stdarg.h> #include <oleacc.h> #include <stdio.h>  void die(char *s) {     // todo }  hwnd mainwin; hwnd dtp1, dtp2, dtp3;  void idealsize(hwnd dtp, char *n, int *x, int *y) {     size s;      s.cx = 0;     s.cy = 0;     printf("%s | %i32d ", n, sendmessagew(dtp, dtm_getidealsize, 0, (lparam) (&s)));     printf("%i32d %i32d\n", s.cx, s.cy);     movewindow(dtp, *x, *y, s.cx, s.cy, true);     *y += s.cy; }  lresult callback wndproc(hwnd hwnd, uint umsg, wparam wparam, lparam lparam) {     int x, y;     size s;      switch (umsg) {     case wm_close:         postquitmessage(0);         return 0;     case wm_size:         x = 10;         y = 10;         idealsize(dtp1, "1", &x, &y);         idealsize(dtp2, "2", &x, &y);         idealsize(dtp3, "3", &x, &y);         break;     }     return defwindowprocw(hwnd, umsg, wparam, lparam); }  static hwnd makedtp(dword style, wchar *format) {     hwnd hwnd;      hwnd = createwindowexw(ws_ex_clientedge,         datetimepick_classw, l"",         style | ws_tabstop | ws_child | ws_visible,         0, 0, 100, 100,         mainwin, null, getmodulehandle(null), null);     if (format != null)         if (sendmessagew(hwnd, dtm_setformat, 0, (lparam) format) == 0)             die("error applying format string date/time picker in finishnewdatetimepicker()");     return hwnd; }  #define gli(what, buf, n) getlocaleinfoex(locale_name_user_default, what, buf, n)  hwnd makedatetimepicker(void) {     wchar *date, *time, *datetime;     int ndate, ntime;     int n;     hwnd hwnd;      // todo verify returns century year     ndate = gli(locale_sshortdate, null, 0);     if (ndate == 0)         die("error getting date string length in uinewdatetimepicker()");     date = (wchar *) malloc(ndate * sizeof (wchar));     if (gli(locale_sshortdate, date, ndate) == 0)         die("error geting date string in uinewdatetimepicker()");      ntime = gli(locale_stimeformat, null, 0);     if (ndate == 0)         die("error getting time string length in uinewdatetimepicker()");     time = (wchar *) malloc(ntime * sizeof (wchar));     if (gli(locale_stimeformat, time, ntime) == 0)         die("error geting time string in uinewdatetimepicker()");      n = _scwprintf(l"%s %s", date, time);     datetime = (wchar *) malloc((n + 1) * sizeof (wchar));     snwprintf(datetime, n + 1, l"%s %s", date, time);     hwnd = makedtp(0, datetime);      free(datetime);     free(time);     free(date);      return hwnd; }  hwnd makedatepicker(void) {     return makedtp(dts_shortdatecenturyformat, null); }  hwnd maketimepicker(void) {     return makedtp(dts_timeformat, null); }  static void makewindows(void) {     mainwin = createwindowexw(0,         l"mainwin", l"full window",         ws_overlappedwindow,         cw_usedefault, cw_usedefault,         500, 500,         null, null, getmodulehandle(null), null);      dtp1 = makedatetimepicker();     dtp2 = makedatepicker();     dtp3 = maketimepicker(); }  void initcommoncontrols(bool);  int main(int argc, char *argv[]) {     wndclassw wc;     msg msg;     hbrush b;      initcommoncontrols(true);      zeromemory(&wc, sizeof (wndclassw));     wc.lpszclassname = l"mainwin";     wc.lpfnwndproc = wndproc;     wc.hinstance = getmodulehandle(null);     wc.hicon = loadiconw(null, idi_application);     wc.hcursor = loadcursorw(null, idc_arrow);     wc.hbrbackground = (hbrush) (color_btnface + 1);     registerclassw(&wc);      makewindows();      showwindow(mainwin, sw_showdefault);     updatewindow(mainwin);      while (getmessagew(&msg, null, 0, 0) > 0) {         translatemessage(&msg);         dispatchmessage(&msg);     }     return 0; }  static const char manifest[] = "<?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"yes\"?>\n<assembly xmlns=\"urn:schemas-microsoft-com:asm.v1\" manifestversion=\"1.0\">\n<assemblyidentity\n    version=\"1.0.0.0\"\n    processorarchitecture=\"*\"\n    name=\"companyname.productname.yourapplication\"\n    type=\"win32\"\n/>\n<description>your application description here.</description>\n<dependency>\n    <dependentassembly>\n        <assemblyidentity\n            type=\"win32\"\n            name=\"microsoft.windows.common-controls\"\n            version=\"6.0.0.0\"\n            processorarchitecture=\"*\"\n            publickeytoken=\"6595b64144ccf1df\"\n            language=\"*\"\n        />\n    </dependentassembly>\n</dependency>\n</assembly>\n";  static ulong_ptr comctlmanifestcookie; static hmodule comctl32;  void initcommoncontrols(bool comctl6) {     wchar temppath[max_path + 1];     wchar filename[max_path + 1];     handle file;     dword nexpected, ngot;     actctx actctx;     handle ac;     initcommoncontrolsex icc;     farproc f;     // listed winapi in both microsoft's , mingw's headers, not on msdn reason     bool (*winapi ficc)(const lpinitcommoncontrolsex);      if (comctl6) {         if (gettemppathw(max_path + 1, temppath) == 0)             die("getting temporary path writing manifest file");         if (gettempfilenamew(temppath, l"manifest", 0, filename) == 0)             die("getting temporary filename writing manifest file");         file = createfilew(filename, generic_write,             0,          // don't share while writing             null, create_always, file_attribute_normal, null);         if (file == null)             die("creating manifest file");         nexpected = (sizeof manifest / sizeof manifest[0]) - 1;     // - 1 omit terminating null character)         if (writefile(file, manifest, nexpected, &ngot, null) == 0)             die("writing manifest file");         if (ngot != nexpected)             die("short write manifest file");         if (closehandle(file) == 0)             die("closing manifest file (this error here because not doing prevent windows being able use manifest file in activation context)");          zeromemory(&actctx, sizeof (actctx));         actctx.cbsize = sizeof (actctx);         actctx.dwflags = actctx_flag_set_process_default;         actctx.lpsource = filename;         ac = createactctx(&actctx);         if (ac == invalid_handle_value)             die("creating activation context synthesized manifest file");         if (activateactctx(ac, &comctlmanifestcookie) == false)             die("activating activation context synthesized manifest file");     }      zeromemory(&icc, sizeof (initcommoncontrolsex));     icc.dwsize = sizeof (initcommoncontrolsex);     icc.dwicc = icc_standard_classes | icc_progress_class | icc_tab_classes | icc_listview_classes | icc_updown_class | icc_bar_classes | icc_date_classes;      comctl32 = loadlibraryw(l"comctl32.dll");     if (comctl32 == null)         die("loading comctl32.dll");     f = getprocaddress(comctl32, "initcommoncontrolsex");     if (f == null)         die("loading initcommoncontrolsex()");     ficc = (bool (*winapi)(const lpinitcommoncontrolsex)) f;     if ((*ficc)(&icc) == false)         die("initializing common controls (comctl32.dll)"); }