objective c - Using MAX and math on array count -


i have misbehaving code looks this: (events nsarray 1 element when code executes)

max(0, self.events.count-2)

i expect result of expression 0, produces -1. checking nsobjcruntime.h, max() looks this:

#define max(a,b)    ({ __typeof__(a) __a = (a); __typeof__(b) __b = (b); __a < __b ? __b : __a; })

with lldb, see following:

(lldb) p (int)[[self events] count] (int) $0 = 1 (lldb) p (int)[[self events] count] - 2 (int) $1 = -1 (lldb) p (bool)[[self events] count] - 2 < 0 (bool) $2 = true (lldb) p (bool)0 > [[self events] count] - 2 (bool) $3 = false

huh? maybe it's operator precedence, but...

(lldb) p (bool)(0 > [[self events] count] - 2) (bool) $4 = no (lldb) p (bool)(0 > ([[self events] count] - 2)) (bool) $5 = no

weird debugger changes on caps bool/yes/no after first funny answer. 1 might suppose foregoing code behave differently:

max(0, self.events.count-2)

...but, , maybe i'm happy sanity here, works wrongly same way. must missing basic syntax, cannot spot it.

the problem due fact count property unsigned. result of unsigned 1 - 2 not -1, it's huge number. huge number returned since greater 0.

but cast unsigned result signed , gets interpreted -1 leaving think result incorrect.

try:

p [[self events] count] - 2

and see large value.


Comments

Post a Comment

Popular posts from this blog

basic authentication with http post params android -

i doing basic authentication passing username , password , using basicnamevaluepair sending post params response service. my method: public stringbuilder callservicehttppost(string username, string password, string type) { // create new httpclient , post header httpclient httpclient = new defaulthttpclient(); httppost httppost = new httppost(webservice + type); httpresponse response = null; stringbuilder total = new stringbuilder(); try { url url = new url(webservice + type); /*string base64encodedcredentials = base64.encodetostring((username + ":" + password).getbytes(), base64.url_safe | base64.no_wrap);*/ string base64encodedcredentials = "basic " + base64.encodetostring( (username + ":" + password).getbytes(), base64.no_wrap); httppost.setheader("auth...
Read more

vb.net - Virtual Keyboard commands -

i wondering difference between virtual these keyboard commands is: keyeventf_extendedkey , keyeventf_keyup is. everywhere have looked gives me description based off integers , not want know each of them does. you've tagged question vb.net, these have nothing @ vb.net. they're constants defined in windows header files, use win32 api functions. as far difference, can't tell looking @ values. individual values not particularly important, that's why named identifiers used. what's important used , documentation functions tells mean. the first one, keyeventf_extendedkey , used keybdinput structure (which used along e.g. sendinput function) pass information synthesized keyboard input. if flag used, means scan code should interpreted extended key. technically, means scan code preceded prefix byte value 224 (&he0 in hexadecimal notation). the second one, keyeventf_keyup , 1 of flags available use structure. means key being released (going up)...
Read more

css - Firefox for ubuntu renders wrong colors -

Image
i've got following problem: i'm developing website, while testing around i've noticed firefox , chromium display css bar in different colors. when switched between several machine come conclusion firefox ubuntu problem. on other devices i've tested website. it's fine. the differences between chrome , firefox rendering: firefox: chromium: note: firefox ubuntu problem. does knows why , came solution? https://bugzilla.mozilla.org/show_bug.cgi?id=655637 bug 629312 - firefox displays wrong colors on image (only linux) open about:config , rechange gfx.color_management.mode 2 0.
Read more