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• Call a C++ constructor from an Objective C class

  - by syvex

  How can I call a C++ constructor from inside an Objective C class? class CppClass { public: CppClass(int arg1, const std::string& arg2): _arg1(arg1), _arg2(arg2) { } // ... private: int _arg1; std::string _arg2; }; @interface ObjC: NSObject { CppClass _cppClass; } @end @implementation ObjC - (id)init { self = [super init]; if ( self ) { // what is the syntax to call CppClass::CppClass(5, "hello") on _cppClass? } return self; } @end

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• += Overloading in C++ problem.

  - by user69514

  I am trying to overload the += operator for my rational number class, but I don't believe that it's working because I always end up with the same result: RationalNumber RationalNumber::operator+=(const RationalNumber &rhs){ int den = denominator * rhs.denominator; int a = numerator * rhs.denominator; int b = rhs.numerator * denominator; int num = a+b; RationalNumber ratNum(num, den); return ratNum; } Inside main //create two rational numbers RationalNumber a(1, 3); a.print(); RationalNumber b(6, 7); b.print(); //test += operator a+=(b); a.print(); After calling a+=(b), a is still 1/3, it should be 25/21. Any ideas what I am doing wrong?

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• What elegant method callback design should be used ?

  - by ereOn

  Hi, I'm surprised this question wasn't asked before on SO (well, at least I couldn't find it). Have you ever designed a method-callback pattern (something like a "pointer" to a class method) in C++ and, if so, how did you do it ? I know a method is just a regular function with some hidden this parameter to serve as a context and I have a pretty simple design in mind. However, since things are often more complex than they seem to, I wonder how our C++ gurus would implement this, preferably in an elegant and standard way. All suggestions are welcome !

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• How to make a C program that can run x86 hex codes

  - by Iowa15

  I have an array of hex codes that translate into assembly instructions and I want to create program in C that can execute these. unsigned char rawData[5356] = { 0x4C, 0x01, 0x0A, 0x00, 0x00, 0x00, 0x00, 0x00, 0x64, 0x0C, 0x00, 0x00, 0x3D, 0x00, 0x00, 0x00, 0x00, 0x00, 0x04, 0x01, 0x2E, 0x74, 0x65, 0x78, 0x74, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xB4, 0x05, 0x00, 0x00, 0xA4, 0x01, 0x00, 0x00, 0x68, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x61, 0x00, 0x00, 0x00, 0x20, 0x00, 0x30, 0x60, 0x2E, 0x64, 0x61, 0x74, 0x61, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x40, 0x00, 0x30, 0xC0, 0x2E, 0x62, 0x73, 0x73, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0x30, 0xC0, 0x2F, 0x34, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x14, 0x00, 0x00, 0x00, 0x58, 0x07, 0x00, 0x00, 0x32, 0x0C, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x20, 0x10, 0x30, 0x60, 0x2F, 0x33, 0x32, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x14, 0x00, 0x00, 0x00, 0x6C, 0x07, 0x00, 0x00,...and so on

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• small string optimization for vector?

  - by BuschnicK

  I know several (all?) STL implementations implement a "small string" optimization where instead of storing the usual 3 pointers for begin, end and capacity a string will store the actual character data in the memory used for the pointers if sizeof(characters) <= sizeof(pointers). I am in a situation where I have lots of small vectors with an element size <= sizeof(pointer). I cannot use fixed size arrays, since the vectors need to be able to resize dynamically and may potentially grow quite large. However, the median (not mean) size of the vectors will only be 4-12 bytes. So a "small string" optimization adapted to vectors would be quite useful to me. Does such a thing exist? I'm thinking about rolling my own by simply brute force converting a vector to a string, i.e. providing a vector interface to a string. Good idea?

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• Manage bad_alloc exception in C++ construtor

  - by Jimmy zhang

  I have Java experience and recently am doing some C++ coding. My question is that if I have class A, in which I have to instantiate class B and class C as two of the member variables of A. If in the constructor of A, should I assume that allocations of class B and C never fail, and handle the bad allocation exception in the destructor of A? If I don't make that assumption, meaning that I add some try catch block to catch bad_alloc of class B and class C, then if the allocation exception occurs, should I do clean up in the constructor of A? What are the recommended practices? If "new" generates a bad allocation, what value does the pointer carry?

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• When do I need to deallocate memory? C++

  - by extintor

  I am using this code inside a class to make a webbrowser control visit a website: void myClass::visitWeb(const char *url) { WCHAR buffer[MAX_LEN]; ZeroMemory(buffer, sizeof(buffer)); MultiByteToWideChar(CP_ACP, MB_ERR_INVALID_CHARS, url, strlen(url), buffer, sizeof(buffer)-1); VARIANT vURL; vURL.vt = VT_BSTR; vURL.bstrVal = SysAllocString(buffer); // webbrowser navigate code... VariantClear(&vURL); } Do I need to do some memory deallocation here?, I see vURL is being deallocated by VariantClear but should I deallocate memory for buffer? I've been told that in another bool I have in the same app I shouldn't deallocate anything because everything clear out when the bool return true/false, but what happens on this void?

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• How to search for a string including spaces in Objective C?

  - by AlexCu

  I have a real basic command-line program, in Objective-C, that searches for user inputed information. Unfourtunately, the code will only read the first word in series of words that the user enters. For example, if the user enters in "Apples are great", only "Apples" is kept (and hence searched later on), excluding the "are great" part of the sentence. Here's what I have so far: char enteredQuery [128]; // array 'name' to hold the scanf string NSString *searchQuery; // ending NSString to hold and compare the user inputed data NSLog(@"Enter search query:"); scanf("%s", enteredQuery); //will read the next line searchQuery = [NSString stringWithCString: enteredQuery encoding: NSASCIIStringEncoding]; //converts scanf data into a NSString type I know it's got to do with me using scanf or the character-encoder conversion, but I can't seem to figure it out. Any help in solving the problem is very appreciated! Thanks.

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• Objective C: App freezes when using a timer

  - by Chris

  It took me hours to figure out how to implement a timer into my program, but when it runs, the app doesn't load completely as it did before the timer. In my main.m: int main (int argc, const char * argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; OutLauncher *theLauncher = [[OutLauncher alloc] init]; NSTimer *theTimer = [theLauncher getTimer]; [theTimer retain]; [[NSRunLoop currentRunLoop] addTimer: theTimer forMode: NSDefaultRunLoopMode]; [[NSRunLoop currentRunLoop] run]; [pool release]; return 0; } The file OutLauncher is being imported into that, which looks like this: - (void)doStuff { NSLog( @"Doing Stuff"); } - (NSTimer *)getTimer{ NSTimer *theTimer; theTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector: @selector(doStuff) userInfo:nil repeats:YES]; return [theTimer autorelease]; } The timer works, the console updates every second with the phrase "doing stuff" but the rest of the program just won't load. It will if I comment out the code I added to int main though

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• UML binary association aggregatee has access to aggregator

  - by user314172

  Firstly, I'd like to thank those who answered my previous question ages ago. Currently I'm engaging more in the design phase UMLs, as this is my first medium scale deployment I'm entrusted with. This is extremely simple, but it bugs me so. If (Component) owns (Manager of Component), and (Manager of Component) has a reference to (Component) through which it manages it; how do you fully describe the relationship? I know it is aggregative, but how do you describe (Manager of Component) possessing a reference/pointer to the (Component) that physically owns the (Manager of Component) ? Example: Lidar owns a LidarManager

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• Strange behaviour of Android debugger in Eclipse when using Camera for preview.

  - by Buzzy

  Hi, I have an Android application that uses a SurfaceView subclass and Camera object to preview images before capture. Once I capture an image, I stop the preview and release the camera. Execution stops at any breakpoint after this. However, apart from the "Suspend" and "Terminate" icons, the rest are disabled. This is strange because the "Debug Current Instruction Pointer" is clearly at the said breakpoint and execution is already suspended. I can't perform any debugging operations and have no option but to terminate the session. Sometimes (very rarely), the session terminates by itself. I can confirm that this odd behavior takes place only after I preview the camera capture. I am fairly new to Android development. Is there some obvious mistake I am making? Any help would be highly appreciated.

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• C++'s unordered_map / hash_map / Google's dense_hash - how to input binary data (buf+len) and insert

  - by shlomif

  Hi all, I have two questions about Google's dense_hash_map, which can be used instead of the more standard unordered_map or hash_map: How do I use an arbitrary binary data memory segment as a key: I want a buffer+length pair, which may still contain some NUL (\0) characters. I can see how I use a NUL-terminated char * string , but that's not what I want. How do I implement an operation where I look if a key exists, and if not - insert it and if it does return the pointer to the existing key and let me know what actually happened. I'd appreciate it if anyone can shed any light on this subject. Regards, -- Shlomi Fish

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• MySQL how to display data from two tables.

  - by gew

  I'm trying to display the username of the person who has submitted the most articles but I don't know how to do it using MySQL & PHP, can someone help me? Here is the MySQL code. CREATE TABLE users ( user_id INT UNSIGNED NOT NULL AUTO_INCREMENT, username VARCHAR(255) DEFAULT NULL, pass CHAR(40) NOT NULL, PRIMARY KEY (user_id) ); CREATE TABLE users_articles ( id INT UNSIGNED NOT NULL AUTO_INCREMENT, user_id INT UNSIGNED mNOT NULL, title TEXT NOT NULL, acontent LONGTEXT NOT NULL, PRIMARY KEY (id) ); Here is the code I have so far. $mysqli = mysqli_connect("localhost", "root", "", "sitename"); $dbc = mysqli_query($mysqli,"SELECT COUNT(*) as coun, user_id FROM users_articles GROUP BY user_id ORDER BY coun DESC LIMIT 1");

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• How to receive a arg from command line in C

  - by 115599yy

  Hi everyone: I want to write a program to receive a argument from command line. It's like a kind of atof(). There my program goes: 9 char s[] = "3.1415e-4"; 10 if (argc == 1) { 11 printf("%e\n",atof(s)); 12 } 13 else if (argc == 2) { 14 //strcpy(s, argv[1]); 15 printf("%e\n",atof(argv[1])); 16 } 1.should I just use argv[1] for the string to pass to my atof(), or, put it into s[]? 2.If I'd better put it in s[], is there some build-in function to do this "put" work? maybe some function like strcpy()?? thanks.

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• calling resize on std vector of pointers crashed

  - by user11869

  The problem can be reproduced using VS 2013 Express. It crashed when internal vector implementation tried to deallocate the original vector. However, the problem can solved by using 'new' instead of 'malloc'. Anyone can shed some light on this? struct UndirectedGraphNode { int label; vector<UndirectedGraphNode *> neighbors; UndirectedGraphNode(int x) : label(x) {}; }; int main(int argc, char** argv) { UndirectedGraphNode* node1 = (UndirectedGraphNode*)malloc(sizeof(UndirectedGraphNode)); node1->label = 0; node1->neighbors.resize(2); return 0; }

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• Write a recursive function in C that converts a number into a string

  - by user3501779

  I'm studying software engineering, and came across this exercise: it asks to write a recursive function in C language that receives a positive integer and an empty string, and "translates" the number into a string. Meaning that after calling the function, the string we sent would contain the number but as a string of its digits. I wrote this function, but when I tried printing the string, it did print the number I sent, but in reverse. This is the function: void strnum(int n, char *str) { if(n) { strnum(n/10, str+1); *str = n%10 + '0'; } } For example, I sent the number 123 on function call, and the output was 321 instead of 123. I also tried exchanging the two lines within the if statement, and it still does the same. I can't figure out what I did wrong. Can someone help please? NOTE: Use of while and for loop statements is not allowed for the exercise.

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• Why is it so hard to build a gtk programe without console using cmake 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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• How can you get the first digit in an int (C#)?

  - by Dinah

  In C#, what's the best way to get the 1st digit in an int? The method I came up with is to turn the int into a string, find the 1st char of the string, then turn it back to an int. int start = Convert.ToInt32(curr.ToString().Substring(0, 1)); While this does the job, it feels like there is probably a good, simple, math-based solution to such a problem. String manipulation feels clunky. Edit: irrespective of speed differences, mystring[0] instead of Substring() is still just string manipulation

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• Is there a way to cause a new C++ class instance to fail, if certain conditions in the contructor ar

  - by Jim Fell

  As I understand it, when a new class is instantiated in C++, a pointer to the new class is returned, or NULL, if there is insufficient memory. I am writing a class that initializes a linked list in the constructor. If there is an error while initializing the list, I would like the class instantiator to return NULL. For example: MyClass * pRags = new MyClass; If the linked list in the MyClass constructor fails to initialize properly, I would like pRags to equal NULL. I know that I can use flags and additional checks to do this, but I would like to avoid that, if possible. Does anyone know of a way to do this? Thanks.

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• How to name variables which are structs

  - by evilpie

  Hello, i often work on private projects using the WinApi, and as you might know, it has thousands of named and typedefed structs like MEMORY_BASIC_INFORMATION. I will stick to this one in my question, what still is preferred, or better when you want to name a variable of this type. Is there some kind of style guide for this case? For example if i need that variable for the VirtualQueryEx function. Some ideas: MEMORY_BASIC_INFORMATION memoryBasicInformation; MEMORY_BASIC_INFORMATION memory_basic_information; Just use the name of the struct non capitalized and with or without the underlines. MEMORY_BASIC_INFORMATION basicInformation; MEMORY_BASIC_INFORMATION information; Short form? MEMORY_BASIC_INFORMATION mbi; I often see this style, using the abbreviation of the struct name. MEMORY_BASIC_INFORMATION buffer; VirtualQueryEx defines the third parameter lpBuffer (where you pass the pointer to the struct), so using this name might be an idea, too. Cheers

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• Why does this program require MSVCR80.dll?

  - by Runner

  #include <gtk/gtk.h> int main( int argc, char *argv[] ) { GtkWidget *window; gtk_init (&argc, &argv); window = gtk_window_new (GTK_WINDOW_TOPLEVEL); gtk_widget_show (window); gtk_main (); return 0; } I tried putting various versions of MSVCR80.dll under the same directory as the generated executable(via cmake),but none matched. Is there a general solution for this kinda problem? UPDATE Some answers recommend install the VS redist,but I'm not sure whether or not it will affect my installed Visual Studio 9, can someone confirm?

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• How to save/export a DOM element to an image?

  - by Don Don

  Hi, I have a web page which has a form element (with its ID known) and inside the form there are multiple DIVs, and the position of each div may be changed. What I'd like to do is: a) Save the current state of this form // var currentForm=document.forms['myFrm'].innerHTML; would probably suffice... b) Save or export the entire form with the most current position of each DIV to an image file. // how to save/export the javascript var of currentForm to an image file is the key question. Any help/pointer would be appreciated.

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• Reading in data from a file into an array

  - by Sam

  If I have an options file along the lines of this: size = 4 data = 1100010100110010 And I have a 2d size * size array that I want to populate the values in data into, what's the best way of doing it? To clarify, for the example I have I'd want an array like this: int[4][4] array = {{1,1,0,0}, {0,1,0,1}, {0,0,1,1}, {0,0,1,0}}. (Not real code but you get the idea). Size can be really be any number though. I'm thinking I'd have to read in the size, maloc an array and then maybe read in a string full of data then loop through each char in the data, cast it to an int and stick it in the appropriate index? But I really have no idea how to go about it, have been searching for a while with no luck. Any help would be cool! :)

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• overflow technique in stack

  - by metashockwave

  int main(void) { problem2(); } void doit2(void) { int overflowme[16]; //overflowme[37] =0; } void problem2(void) { int x = 42; doit2(); printf("x is %d\n", x); printf("the address of x is 0x%x\n", &x); } Would someone help me understand why overflowme[37] =0; from the doit2 function will overwrite the value of x? (please include Program Counter and Frame Pointer of the function doit2 in your explanation) Thank you! It works every time with Project properties-Configuration properties-C/C++ -Code Generation-Basic Runtime Checks set to "Default". so it's not an undefined behavior.

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• GCC fatal error: stdio.h: No such file or directory

  - by user2615799

  I'm trying to compile a program in C on OS X 10.9 with GCC 4.9 (experimental). For some reason, I'm getting the following error at compile time: gcc: fatal error: stdio.h: No such file or directory I then tried a simple Hello World program: #include <stdio.h> int main(int *argc, const char *argv[]) { printf("Hello, world!"); return 0; } Again, upon running gcc -o ~/hello ~/hello.c, I got the same error. I'm using an experimental version of gcc, but it seems implausible that there would be a release which generated errors upon importing stdio. What could be causing this issue, and how can it be fixed?

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