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• strange results with /fp:fast

  - by martinus

  We have some code that looks like this: inline int calc_something(double x) { if (x > 0.0) { // do something return 1; } else { // do something else return 0; } } Unfortunately, when using the flag /fp:fast, we get calc_something(0)==1 so we are clearly taking the wrong code path. This only happens when we use the method at multiple points in our code with different parameters, so I think there is some fishy optimization going on here from the compiler (Microsoft Visual Studio 2008, SP1). Also, the above problem goes away when we change the interface to inline int calc_something(const double& x) { But I have no idea why this fixes the strange behaviour. Can anyone explane this behaviour? If I cannot understand what's going on we will have to remove the /fp:fastswitch, but this would make our application quite a bit slower.

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• STL member variable initalization issue with windows API

  - by Django

  I am creating a windows app that uses a vector of stings as a member variable. For some reason, I can compile but when it tries to get at any of the vectors members is crashes. the error is 0xC0000005: Access violation reading location 0xcdcdcdd9. in the member function of the vector class. this is the size() function where it breaks. size_type capacity() const { // return current length of allocated storage return (this->_Myend - this->_Myfirst); } I am using visual studios 2010. thank you Django

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• Retain cycle on `self` with blocks

  - by Jonathan Sterling

  I'm afraid this question is pretty basic, but I think it's relevant to a lot of Objective-C programmers who are getting into blocks. What I've heard is that since blocks capture local variables referenced within them as const copies, using self within a block can result in a retain cycle, should that block be copied. So, we are supposed to use __block to force the block to deal directly with self instead of having it copied. __block typeof(self) bself = self; [someObject messageWithBlock:^{ [bself doSomething]; }]; instead of just [someObject messageWithBlock:^{ [self doSomething]; }]; What I'd like to know is the following: if this is true, is there a way that I can avoid the ugliness (aside from using GC)?

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• Best way to insert items from a Derived class's constructor into a Base class's private std::vector?

  - by Will

  I have these classes: class Base { ... private: std::vector<X> v; }; class Derived { Derived(X*, int n); } where the constructor of Derived is passed an array of item Xs, which I need to insert into my vector v in the Base class. (X is a smart pointer) Currently I see two ways to do this: 1) Create a function in Base: InsertItem(X*) that will insert an item into the vector. 2) Create a vector in Derived that contains the full list, then get it into Base by moving the entire vector. I dont see any advantages to #2, but was wondering if #1 was a good solution, or if there are better ways to do this. Thanks!

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• Does a static object within a function introduce a potential race condition?

  - by Jeremy Friesner

  I'm curious about the following code: class MyClass { public: MyClass() : _myArray(new int[1024]) {} ~MyClass() {delete [] _myArray;} private: int * _myArray; }; // This function may be called by different threads in an unsynchronized manner void MyFunction() { static const MyClass _myClassObject; [...] } Is there a possible race condition in the above code? Specifically, is the compiler likely to generate code equivalent to the following, "behind the scenes"? void MyFunction() { static bool _myClassObjectInitialized = false; if (_myClassObjectInitialized == false) { _myClassObjectInitialized = true; _myClassObject.MyClass(); // call constructor to set up object } [...] } ... in which case, if two threads were to call MyFunction() nearly-simultaneously, then _myArray might get allocated twice, causing a memory leak? Or is this handled correctly somehow?

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• How to change FPU context in signal handler (C++/Linux)

  - by Henry Fané

  I wrote a signal handler to catch FPE errors. I need to continue execution even if this happens. I receive a ucontext_t as parameter, I can change the bad operand from 0 to another value but the FPU context is still bad and I run into an infinite loop ? Does someone already manupulate the ucontext_t structure on Linux ? I finally found a way to handle these situations by clearing the status flag of ucontext_t like this: ... const long int cFPUStatusFlag = 0x3F; aContext->uc_mcontext.fpregs->sw &= ~cFPUStatusFlag; ... 0x3F is negated to put 0 in the 6 bits of the status register of the FPU (x87). Doing this implies to check for FPE exceptions after calculation.

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• Treat a void function as a value

  - by Brendan Long

  I'm writing some terrible, terrible code, and I need a way to put a free() in the middle of a statement. The actual code is: int main(){ return printf("%s", isPalindrome(fgets(malloc(1000), 1000, stdin))?"Yes!\n":"No!\n") >= 0; // leak 1000 bytes of memory } I was using alloca(), but I can't be sure that will actually work on my target computer. My problem is that free returns void, so my code has this error message: error: void value not ignored as it ought to be The obvious idea I had was: int myfree(char *p){ free(p); return 0; } Which is nice in that it makes the code even more unreadable, but I'd prefer not to add another function. I also briefly tried treating free() as a function pointer, but I don't know if that would work, and I don't know enough about C to do it properly. Note: I know this is a terrible idea. Don't try this at home kids.

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• Flipping around a div using Javascript

  - by Isaac Copper

  Flip is a great JQuery plugin for flipping blocks, but it doesn't preserve the background while it animates the flip. For example, I have this pretty background, here, before I flip. While flipping, it gets ugly: here. Is there a way I can flip this div nicely, keeping the pretty background I have, and maybe even achieve a smoother animation than I can get with Flip? If I need to dive into this headfirst and code my own function for flipping a div, that's also doable, and I'd really appreciate some pointer there, if that's what I must do. Thanks so much!

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• How to vertically align images in <td>

  - by Ricky

  I got a <td> where two images () reside shown as follows. One is much higher than the other. How do I let the shorter one align to the top of <td />? <td style="padding-left: 0px; cursor: pointer; vertical-align: top;"> <img width="85px" src=".../xyz.png"/> <img src=".../icon_live.gif" /> // shorter one </td>

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• Javascript handling textarea

  - by bbenton

  Hi all, I'm a bit new to Javascript and am trying to create a delimited string from a textare. The problem is when passing in the textarea, it adds newlines for each row on the textarea. I need to have the entire textarea parsed into a string with a delimiter for each line (replacing the newline char). So for example, if you passed in a textarea with the following lines (which is also how it looks when using the alert function): abcd efgh ijkl It would look like: abcd-efgh-ijkl after parsing. function submitToForm(form) { var param_textarea = form.listofplugins.value; var test = param_textarea.replace(/\\r?\\n/, /:/) alert(test); } Thanks a lot!

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• What's void *userData exactly?

  - by mystify

  In a C function declaration, I have seen this parameter definition: void *userData so, what exactly is that? My guess: the void says it can be anything arbitrary, or even nothing. Almost similar to id of objective-c. It just allows to pass in whatever data structure you like. The star in front of userData says, that the argument must be passed in by reference. So when using this stuff in the function body, typically it must be casted and dereferenced. So if I pass in an pointer to SomeClass instance, I would get that like this: SomeClass *myObj = (SomeClass*)userData; In the case I had nothing special to pass along, I would provide NULL as argument. Are my assumptions correct? Or did I get something wrong?

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• Potential problems porting to different architectures

  - by Brendan Long

  I'm writing a Linux program that currently compiles and works fine on x86 and x86_64, and now I'm wondering if there's anything special I'll need to do to make it work on other architectures. What I've heard is that for cross platform code I should: Don't assume anything about the size of a pointer, int or size_t Don't make assumptions about byte order (I don't do any bit shifting -- I assume gcc will optimize my power of two multiplication/division for me) Don't use assembly blocks (obvious) Make sure your libraries work (I'm using SQLite, libcurl and Boost, which all seem pretty cross-platform) Is there anything else I need to worry about? I'm not currently targeting any other architectures, but I expect to support ARM at some point, and I figure I might as well make it work on any architecture if I can. Also, regarding my second point about byte order, do I need to do anything special with text input? I read files with getline(), so it seems like that should be done automatically as well.

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• Template class implicit copy constructor issues

  - by Nate

  Stepping through my program in gdb, line 108 returns right back to the calling function, and doesn't call the copy constructor in class A, like (I thought) it should: template <class S> class A{ //etc... A( const A & old ){ //do stuff... } //etc... }; template <class T> class B{ //etc... A<T> ReturnsAnA(){ A<T> result; // do some stuff with result return result; //line 108 } //etc... }; Any hints? I've banged my head against the wall about this for 4 hours now, and can't seem to come up with what's happening here.

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• Accessing Password Protected Network Drives in Windows in C#?

  - by tkeE2036

  Hi Everyone, So in C# I am trying to access a file on a network, for example at "//applications/myapp/test.txt", as follows: const string fileLocation = @"//applications/myapp/test.txt"; using (StreamReader fin = new StreamReader(FileLocation)) { while(!fin.EndOfStream()){ //Do some cool stuff with file } } However I get the following error: System.IO.IOException : Logon failure: unknown user name or bad password. I figure its because I need to supply some network credentials but I'm not sure how to get those to work in this situation. Does anyone know the best way (or any way) to gain access to these files that are on a a password protected location? Thanks in advance!!

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• Real thing about "->" and "."

  - by fsdfa

  I always wanted to know what is the real thing difference of how the compiler see a pointer to a struct (in C suppose) and a struct itself. struct person p; struct person *pp; pp->age, I always imagine that the compiler does: "value of pp + offset of atribute "age" in the struct". But what it does with person.p? It would be almost the same. For me "the programmer", p is not a memory address, its like "the structure itself", but of course this is not how the compiler deal with it. My guess is it's more of a syntactic thing, and the compiler always does (&p)->age. I'm correct?

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• jQuery click event not working when mouse moves from one div to another with button held down

  - by Acorn

  I've made a page that uses jQuery to allow you to place <div>s on the page based on your mouse coordinates when you click. The page And here's the javascript: $('document').ready(function() { $("#canvas").click(function(e){ var x = e.pageX - this.offsetLeft; var y = e.pageY - this.offsetTop; $(document.createElement('div')).css({'left':x + 'px', 'top':y + 'px'}).addClass('tile').appendTo('#canvas'); }); }); I've found that if you mousedown in the div#canvas and mouseup with your pointer over a placed <div> (or vice versa) then a new <div> doesn't get placed. Why is this?

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• <function> referenced from; symbol(s) not found.

  - by jfm429

  I have a piece of C code that is used from a C++ function. At the top of my C++ file I have the line: #include "prediction.h" In prediction.h I have this: #ifndef prediction #define prediction #include "structs.h" typedef struct { double estimation; double variance; } response; response runPrediction(int obs, location* positions, double* observations, int targets, location* targetPositions); #endif I also have prediction.c, which has: #include "prediction.h" response runPrediction(int obs, location* positions, double* observations, int targets, location* targetPositions) { // code here } Now, in my C++ file (which as I said includes prediction.h) I call that function, then compile (through Xcode) I get this error: "runPrediction(int, location*, double*, int, location*)", referenced from: mainFrame::respondTo(char*, int)in mainFrame.o ld: symbol(s) not found collect2: ld returned 1 exit status prediction.c is marked for compilation for the current target. I don't have any problems with other .cpp files not being compiled. Any thoughts here?

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• Android internet connectivity check problem

  - by Chaoz

  Hello, I'm new to Android development and working on an Android application that requires the phone to be connected to the internet, through either Wifi, EDGE or 3G. This is the code that I'm using: public static boolean isConnected() { ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE); return cm.getActiveNetworkInfo().isConnectedOrConnecting(); } I've also set these permissions in the manifest file: <uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> This works fine in the emulator running version 1.5 of Android when 3G is enabled, but it crashes when I disable the 3G connection. My application throws a null pointer exception when I call isConnectedOrConnecting(). Hope that anyone knows the solution to this. Thanks in advance!

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• C++ STL map.find() not finding my stuff

  - by Joe

  Hello, I have constructed a map and loaded it with data. If I iterate over all the elements I see they are all valid. However, the find method doesn't find my item. I'm sure it's something stupid I am doing. Here is snippet: // definitions // I am inserting a person class and using the firstname as the key typedef std::map<char*,Person *> mapType; mapType _myMap; mapType::iterator _mapIter; ... Person *pers = new Person(FirstName, LastName, Address, Phone); _myMap.insert(make_pair(pers->firstName, pers); ... ...later.... _mapIter = _myMap.find(firstName); // returns map.end _mapIter = _myMap.find("joe"); // returns map.end and I have no idea why :(

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• Lazy evaluation with ostream C++ operators

  - by SavinG

  I am looking for a portable way to implement lazy evaluation in C++ for logging class. Let's say that I have a simple logging function like void syslog(int priority, const char *format, ...); then in syslog() function we can do: if (priority < current_priority) return; so we never actually call the formatting function (sprintf). On the other hand, if we use logging stream like log << LOG_NOTICE << "test " << 123; all the formating is always executed, which may take a lot of time. Is there any possibility to actually use all the goodies of ostream (like custom << operator for classes, type safety, elegant syntax...) in a way that the formating is executed AFTER the logging level is checked ?

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• C# Convert negative int to 11 bits

  - by Klemenko

  I need to convert numbers in interval [–1024, 1016]. I'm converting to 11 bits like that: string s = Convert.ToString(value, 2); //Convert to binary in a string int[] bits = s.PadLeft(11, '0') // Add 0's from left .Select(c => int.Parse(c.ToString())) // convert each char to int .ToArray(); // Convert IEnumerable from select to Array This works perfectly for signed integers [0, 1016]. But for negative integers I get 32 bits result. Do you have any idea how to convert negative integers to 11 bits array?

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• Removing a UIView from its superView and expanding its frame to full screen

  - by Magic Bullet Dave

  I have an object that is a subclass of UIView that can be added to a view hierarchy as a subView. I want to be able to remove the UIView from its superView and add it as a subView of the main window and then expand to full screen. Something along the lines of: // Remove from superView and add to mainWindow [self retain]; [self removeFromSuperView]; [self addSubView:mainWindow]; // Animate to full screen [UIView beginAnimations:@"expandToFullScreen" context:nil]; [UIView setAnimationDuration:1.0]; self.frame = [[UIScreen mainScreen] applicationFrame]; [UIView commitAnimations]; [self release]; Firstly am I on the right lines? Secondly, is there an easily way for the object to get a pointer to the mainWindow? Thanks Dave

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• OpenGL texture not showing up on some computers, problem with auxDIBImageLoad?

  - by CptanPanic

  I have a simple openGL GUI that has uses a bmp as a texture. The problem is on some computers the texture doesn't show up. But on ones with newer OpenGL drivers it works. How can I make it more compatible. I think the problem may be with auxDIBImageLoad. When I inspect the result, I see the x,y correct, but the data pointer points to memory bank with all zeros. What could be wrong?

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• How can I require an attribute on a class definition?

  - by spoulson

  Is there a way to enforce a compile requirement for certain attributes on a class or interface implementation? For example, let's say my application uses a series of static classes that contain const int resource values. I'd like to decorate the class in a Description attribute to describe its contents. In concept, I'd like to apply this attribute requirement to an interface, then each static class would implement it with its required Description. I could write a run-time check or a unit test to check compliance. But really a compile-time check would be best. Is there such a thing?

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• Why is it so hard to build a gtk programe without console using gtk in windows?

  - by Runner

  I'm following the tuto: http://zetcode.com/tutorials/gtktutorial/firstprograms/ It works but each time I double click on the executable,there is a console which I don't want it there. How do I get rid of that console? I tried this: add_executable(Cmd WIN32 cmd.c) But got this fatal error: MSVCRTD.lib(crtexew.obj) : error LNK2019: unresolved external symbol _WinMain@16 referenced in function ___tmainCRTStartup Cmd.exe : fatal error LNK1120: 1 unresolved externals While using gcc directly works: gcc -o Cmd cmd.c -mwindows .. I'm guessing it has something to do with the entry function: int main( int argc, char *argv[]),but why gcc works? How can I make it work with cmake?

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