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  • Preprocessor #define vs. function pointer - best practice?

    - by Dustin
    I recently started a small personal project (RGB value to BGR value conversion program) in C, and I realised that a function that converts from RGB to BGR can not only perform the conversion but also the inversion. Obviously that means I don't really need two functions rgb2bgr and bgr2rgb. However, does it matter whether I use a function pointer instead of a macro? For example: int rgb2bgr (const int rgb); /* * Should I do this because it allows the compiler to issue * appropriate error messages using the proper function name, * not to mention possible debugging benefits? */ int (*bgr2rgb) (const int bgr) = rgb2bgr; /* * Or should I do this since it is merely a convenience * and they're really the same function anyway? */ #define bgr2rgb(bgr) (rgb2bgr (bgr)) I'm not necessarily looking for a change in execution efficiency as it's more of a subjective question out of curiosity. I am well aware of the fact that type safety is neither lost nor gained using either method. Would the function pointer merely be a convenience or are there more practical benefits to be gained of which I am unaware?

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  • What time function do I need to use with pthread_cond_timedwait?

    - by Vincent
    The pthread_cond_timedwait function needs an absolute time in a time timespec structure. What time function I'm suppose to use to obtain the absolute time. I saw a lot of example on the web and I found almost all time function used. (ftime, clock, gettimeofday, clock_gettime (with all possible CLOCK_...). The pthread_cond_timedwait uses an absolute time. Will this waiting time affected by changing the time of the machine? Also if I get the absolute time with one of the time function, if the time of the machine change between the get and the addition of the delta time this will affect the affect the wait time? Is there a possibility to wait for an event with a relative time instead?

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  • FF extension. how to show data extracted in a javascript function to the dropdown menu in the browse

    - by encryptor
    I am developing a ff extension. On one menupopup, the onpopupshowing calls a javascript function. Tha JS function extracts a list of names. Now these names have to be displayed in the same popup. How can i get this? Basically i will need to pass the data (just as we use beans in java) to the browser from the JS function. The data can change everytime the popup is called.

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  • Is there any way to retrieve a float from a varargs function's parameters?

    - by Jared P
    If the function was defined with a prototype which explicitly stated the types of the parameters, eg. void somefunc(int arg1, float arg2); but is implemented as void somefunc(int arg1, ...) { ... } is it possible to use va_arg to retrieve a float? It's normally prevented from doing this because varargs functions have implicit type promotions, like float to double, so trying to retrieve an unpromoted type is unsupported, even though the function is being called with the unpromoted type do to the more specific function prototype. The reason for this is to retrieve arguments of different types at runtime, as part of an obj-c interpreter, where one function will be reused for all different types of methods. This would be best as architecture independent (so that if nothing else the same code works on simulator and on device), although if there is no way to do this then device specific fixes will be accepted.

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  • Call load using a div id that has been passed into a function, div id is a parameter

    - by tittatty
    I am dynamically creating divs within a jquery accordion that are loaded with data as when the user clicks on the accordion title. I have this all working except that when I pass the div id into the load details method, the call to .load() does not work. What can I do to fix this? It seems like a simple javascript string eval would work but I can not find what I am looking for. Code: Here is the basic function: function loadDetails(div_id) { var load_string = "ajax/get_details.aspx"; $(div_id).load(load_string); } This function is called correctly on the click event and the div_id is passed in correctly but the load function is not working. If I use code like this it work correctly: $('#test').load(load_string);

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  • Within a DLL, how is the function table structured?

    - by Willi Ballenthin
    I've been looking into the implementation of a device library that doesn't explicitly support my operating system. In particular, I have a disassembled DLL, and a fair amount of supporting source code. Now, how is the function table/export table structured? My understanding is that the first structure of the .data section is a table of VRAs. Next is a table of strings linked by index to that first address table. This makes sense to me, as a linker could translate between symbols and addresses. How do functions referenced by ordinals fit into this picture? How does one know which function has such and such ordinal number, and how does the linker resolve this? In other words, given that some other DLL imports SOME_LIBRARY_ordinal_7, how does the linker know which function to work with? Thanks, all! edit More information... Im working with the FTDI libraries, and would like to resolve which function is being invoked. In particular, I see something like: extern FTD2XX_Ordinal_28: near how might I go about determining which function is being referenced, and how does the linker do this?

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  • What's the point of the javascript navigator.javaEnabled function?

    - by den shade
    The navigator object has a javaEnabled function that indicates if the browser has javascript support. This seems to be a little odd: If JS is indeed enabled the function will return true, well obviously. If JS is disabled it will return <nothing since it is never run, javaScript is disabled. I must be missing something here, or is it really that useless this function?

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  • Do I need to specify a return type for an anonymous function in javascript / typescript?

    - by Anne
    I have the following function: $('td:eq(' + iColumn + ') input', oSettings.oApi._fnGetTrNodes(oSettings)) .each(function () { aData.push(this.value); }); In typescript I am getting a message saying: Error 3 Function declared a non-void return type, but has no return expression Why am I getting this message? I can resolve the message by saying "return true". Should I always specify a return type for this?

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  • C++: static function member shared between threads, can block all?

    - by mhambra
    Hi all, I have a class, which has static function defined to work with C-style extern C { static void callback(foo bar) { } }. // static is defined in header. Three objects (each in separate pthread) are instantiated from this class, each of them has own loop (in class constructor), which can receive the callback. The pointer to function is passed as: x = init_function(h, queue_id, &callback, NULL); while(1) { loop_function(x); } So each thread has the same pointer to &callback. Callback function can block for minutes. Each thread object, excluding the one which got the blocking callback, can call callback again. If the callback function exists only once, then any thread attempting to callback will also block. This would give me an undesired bug, circa is interesting to ask: can anything in C++ become acting this way? Maybe, due to extern { } or some pointer usage?

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  • how could it works if function is called before it is defined in python?

    - by user2131316
    I was wondering what does if __name__ == "__main__": really do in python, I have the following code in python3: def main(): test(); def test(): print("hello world " + __name__); if __name__ == "__main__": main(); we know that we have to declare a function before we use it, so function call inside of if part works fine, the main() is defined before it is called inside of if statement, but what about the test() function, it is defined after it is called and there is no errors: def main(): test(); def test(): print("hello world " + __name__); so how could it works if the test() function is defined after it is called?

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  • How to differentiate between method and function in a decorator?

    - by defnull
    I want to write a decorator that acts differently depending on whether it is applied to a function or to a method. def some_decorator(func): if the_magic_happens_here(func): # <---- Point of interest print 'Yay, found a method ^_^ (unbound jet)' else: print 'Meh, just an ordinary function :/' return func class MyClass(object): @some_decorator def method(self): pass @some_decorator def function(): pass I tried inspect.ismethod(), inspect.ismethoddescriptor() and inspect.isfunction() but no luck. The problem is that a method actually is neither a bound nor an unbound method but an ordinary function as long as it is accessed from within the class body. What I really want to do is to delay the actions of the decorator to the point the class is actually instantiated because I need the methods to be callable in their instance scope. For this, I want to mark methods with an attribute and later search for these attributes when the .__new__() method of MyClass is called. The classes for which this decorator should work are required to inherit from a class that is under my control. You can use that fact for your solution. In the case of a normal function the delay is not necessary and the decorator should take action immediately. That is why I wand to differentiate these two cases.

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  • How can i get my delete messages function just appear for the user's own messages left on their friends page?

    - by Hannah_B
    I had been working on this trying the delete message button to work on my own profile page of my site. When I delete a message left by a friend it not only deletes it from the screen but deletes it from the database. The messages in the database have 4 fields: message_id, from, to and message. Here is my profile view that shows how Im deleting messages from my friends: if(!empty($messages)){ foreach($messages as $message): $delete = $message['message_id']; //var_dump($message); ?> <li><?=$message['from']?> says...: "<?=$message['message']?>"(<?=anchor("home/deleteMsg/$delete", 'delete')?>)</li> //this is where the delete button appears beside messages left <?php endforeach?> <?php }else{ ?> <?php echo 'No messages left yet !!!'; }?> Here is my controller showing the deleteMsg function called: function deleteMsg($messageid) { $this->messages->deleteMsg($messageid); redirect('home'); } Here is the messages model showing the deleteMsg model itself: function deleteMsg($message_id) { $this->db->where(array('message_id' => $message_id)); $this->db->delete('messages'); } Here is my friendprofile view where I want to implement the delete message command just so the button appears for messages Ive left and I can delete them. The delete button will not appear beside other friends comments on this page: <li><?=$message['from']?> says...: "<?=$message['message']?>"</li> Now I've tried creating a new delete Message function to no success so far, am I better off doing this than calling the same function? As this didnt work either.

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  • Does the compiler optimize the function parameters passed by value?

    - by Naveen
    Lets say I have a function where the parameter is passed by value instead of const-reference. Further, lets assume that only the value is used inside the function i.e. the function doesn't try to modify it. In that case will the compiler will be able to figure out that it can pass the value by const-reference (for performance reasons) and generate the code accordingly? Is there any compiler which does that?

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  • Move document.ready function to a separate javascript fucntion?

    - by tonsils
    Hi, Is it possible to move the following code within a jQuery document.ready function into a separate javascript function, so that it can be called just like any other javascript function, i.e.: <script type="text/javascript"> $(document).ready(function() { $('div#infoi img[title]').qtip({ position: { adjust: { x:-110, y:0 }, corner: { target: 'bottomLeft', tooltip: 'topMiddle' } }, style: { width: 250, padding: 5, background: '#E7F1FA', color: 'black', textAlign: 'center', border: { width: 3, color: '#65a9d7' }, tip: 'topRight' } }); }); </script> If yes, then how - if not, then that answers my question. Thanks.

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  • changing the bg color of an active click function in jquery?

    - by pingpong
    basically i have this click function in jquery: (this is just a snippet, not full) $('.block').click(function(){ var id= $(this).attr('id'); i want to chnage the background color of the block that has been clicked only, assigned with the id i.e. $('.block').click(function(){ var id= $(this).attr('id'); $('.block').css('background-color','grey'); but where do i assign the id, so jquery knows, to only turn the clicked block into grey, not the others, cheers

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  • What is the purpose of this string argument in a JavaScript function?

    - by Adel
    In the following function, there is the line: var username=getCookie("username"); Here's the whole function: function checkCookie() { var username=getCookie("username"); if (username!=null && username!="") { alert("Welcome again " + username); } else { username=prompt("Please enter your name:",""); if (username!=null && username!="") { setCookie("username",username,365); } } What is the point of the "username" argument being passed above? function getCookie(c_name) { var i,x,y,ARRcookies=document.cookie.split(";"); for (i=0;i<ARRcookies.length;i++) { x=ARRcookies[i].substr(0,ARRcookies[i].indexOf("=")); y=ARRcookies[i].substr(ARRcookies[i].indexOf("=")+1); x=x.replace(/^\s+|\s+$/g,""); if (x==c_name) { return unescape(y); } } } The whole code is here Thanks!

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  • Writing a jquery plugin in coffeescript - how to get "(function($)" and "(jQuery)"?

    - by PandaWood
    I am writing a jquery plugin in coffeescript but am not sure how to get the function wrapper part right. My coffeescript starts with this line: $.fn.extend({ Which creates the javascript with a function wrapper: (function() { $.fn.extend({ but I want a '$' passed in like this: (function($) { $.fn.extend({ Similar for the ending I have... nothing in particular in coffeescript. I get this in javascript: })(); But would like this: })(jQuery); Does anyone know how to achieve this with the coffeescript compiler? Or what is the best way to get this done within coffeescript?

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  • What happens in memory when calling a function with literal values?

    - by Drise
    Suppose I have an arbitrary function: void someFunc(int, double, char); and I call someFunc(8, 2.4, 'a');, what actually happens? How does 8, 2.4, and 'a' get memory, moved into that memory, and passed into the function? What type of optimizations does the compiler have for situations like these? What if I mix and match parameters, such like someFunc(myIntVar, 2.4, someChar);? What happens if the function is declared as inline?

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  • Does a native php (5+) function exist that does the following in 1 line?

    - by Vinh
    function array_value_from_key($array,$key) { return !empty($array[$key]) ? $array[$key] : null; } The reason I ask is because I have a class function that returns an array. Instead of having to do $myArray = myClass::giveMeArray(); $myValue = $myArray[$myKey]; I'd like to do something along the lines of $myValue = array_value_from_key(myClass::giveMeArray(),$myKey); When an object is returned, you can chain the object such as $myValue = myClass::giveMeObject()->aValue; Voila, nice and clean.. not being able to find what seems to be a simple and trivial function is driving me crazy... PS.. one more example of how I'd like to use such a function if(arrayKeyVal(aClass::giveMeArray(),$myKey)) { do_something(); }

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  • How can I map a String to a function in Java?

    - by Bears will eat you
    Currently, I have a bunch of Java classes that implement a Processor interface, meaning they all have a processRequest(String key) method. The idea is that each class has a few (say, <10) member Strings, and each of those maps to a method in that class via the processRequest method, like so: class FooProcessor implements Processor { String key1 = "abc"; String key2 = "def"; String key3 = "ghi"; // and so on... String processRequest(String key) { String toReturn = null; if (key1.equals(key)) toReturn = method1(); else if (key2.equals(key)) toReturn = method2(); else if (key3.equals(key)) toReturn = method3(); // and so on... return toReturn; } String method1() { // do stuff } String method2() { // do other stuff } String method3() { // do other other stuff } // and so on... } You get the idea. This was working fine for me, but now I need a runtime-accessible mapping from key to function; not every function actually returns a String (some return void) and I need to dynamically access the return type (using reflection) of each function in each class that there's a key for. I already have a manager that knows about all the keys, but not the mapping from key to function. My first instinct was to replace this mapping using if-else statements with a Map<String, Function>, like I could do in Javascript. But, Java doesn't support first-class functions so I'm out of luck there. I could probably dig up a third-party library that lets me work with first-class functions, but I haven't seen any yet, and I doubt that I need an entire new library. I also thought of putting these String keys into an array and using reflection to invoke the methods by name, but I see two downsides to this method: My keys would have to be named the same as the method - or be named in a particular, consistent way so that it's easy to map them to the method name. This seems WAY slower than the if-else statements I have right now. Efficiency is something of a concern because these methods will tend to get called pretty frequently, and I want to minimize unnecessary overhead. TL; DR: I'm looking for a clean, minimal-overhead way to map a String to some sort of a Function object that I can invoke and call (something like) getReturnType() on. I don't especially mind using a 3rd-party library if it really fits my needs. I also don't mind using reflection, though I would strongly prefer to avoid using reflection every single time I do a method lookup - maybe using some caching strategy that combines the Map with reflection. Thoughts on a good way to get what I want? Cheers!

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  • jquery - How do i call the same function with different div ids?

    - by Nahom
    Hi, I have two divs with different ids (#washing,#bleaching). How can i use a function for different id's. I have tried adding both the ids together $("#washing, #bleaching"), but the function is not working correctly on the divs. Can anyone please help me... Here is the code $(function() { $("#washing").paginate({ count: 10, start: 1, display: 7, border: true, border_color: '#fff', onChange: function(page) { $('._current', '#paginationdemo').removeClass('_current').hide(); $('#p' + page).addClass('_current').show(); } }); });

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  • Javascript: can I call a function in an external file from the main page ?

    - by Patrick
    hi, I'm loading from my main page an external js file, with a function. I have a flash file in the main page invoking the javascript function. Everything worked very well until when the javascript code was in the main file, but when I moved javascript to an external file the function seems not called anymore. So... there is no way to move the javascript code to an external file ? Or any other solution ? thanks

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  • Can't use MySQL extract() function in the WHERE clause.

    - by UkraineTrain
    I've run the following query: UPDATE main_table, reference_table SET main_table.calc_column = (CASE WHEN main_table.incr = "6AM" THEN reference_table.col1+reference_table.col2+... WHEN main_table.incr = "12AM" THEN reference_table.col7+reference_table.col8+... WHEN main_table.incr = "6PM" THEN reference_table.col13+reference_table.col14+... ELSE reference_table.col19+reference_table.col20+...) WHERE main_table.month = extract(month from reference_table.thedate) AND main_table.day = extract(day from reference_table.thedate) I've used extract() function since my reference_table doesn't have month and day columns but has the date column named thedate. I've used the extract() function on the reference_table many times before successfully, so, I know that there's nothing wrong with my extract function syntax. However, in this instance, MySQL complains. It probably has to do with the fact that I've used in the WHERE clause. I know that this issue could get fixed if I added the month and day columns to the reference_table to avoid using the extract() function. However, I'm very reluctant to do that and would like to avoid it. How can I make it work?`

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  • lua - how to call function from above it in code (prior to it being defined)?

    - by Greg
    what is the syntax (i.e. code example) in Lua so you can call a function prior to it being defined? i.e. how do you kind of create the function, but then add it's implementation further down in code. So roughly like this: define function name (doX) here somehow (i.e. subject of this question) call doX here (further down in the code) doX implemention here (i.e. all functions down at the bottom of the file)

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