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  • C++ operator[] syntax.

    - by Lanissum
    Just a quick syntax question. I'm writing a map class (for school). If I define the following operator overload: template<typename Key, typename Val> class Map {... Val* operator[](Key k); What happens when a user writes: Map<int,int> myMap; map[10] = 3; Doing something like that will only overwrite a temporary copy of the [null] pointer at Key k. Is it even possible to do: map[10] = 3; printf("%i\n", map[10]); with the same operator overload?

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  • Memory allocated with malloc does not persist outside function scope?

    - by PM
    Hi, I'm a bit new to C's malloc function, but from what I know it should store the value in the heap, so you can reference it with a pointer from outside the original scope. I created a test program that is supposed to do this but I keep getting the value 0, after running the program. What am I doing wrong? int f1(int * b) { b = malloc(sizeof(int)); *b = 5; } int main() { int * a; f1(a); printf("%d\n", a); return 0; }

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  • freeing malloc and checkin it is empty or not

    - by gcc
    char *p; p="kjkjk"; . .//there are codes which are checking another command . if(.....)//i used pointer p in only that area free(p); . . //there are codes which are checking another command . if(p==NULL) //i check whether is empty .... if(p==-1) //can we use "EOF==p " in if statement ... //are there any usage like that EOF==p else .... I think there is big error , but where?

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  • Button border radius and cursor

    - by noober
    CSS border radius does affect button rendering (I see it's round form), but does not affect how it interacts with the user (I still can click button outside its border). How should I fix it? I see the behavior in Chrome. button { cursor: pointer; outline: none; background-size: 100% 100%; background-color: red; /*transparent;*/ /* It's actually red and ROUND. */ background-position: center center; background-repeat: no-repeat; border: 0px; -webkit-border-top-left-radius: 73px; -webkit-border-top-right-radius: 73px; -webkit-border-bottom-left-radius: 73px; -webkit-border-bottom-right-radius: 73px; width: 146px; height: 146px; background-image: url('leftarrow.png'); } Regards,

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  • C++ function call routes resolver

    - by Poni
    Hi! I'm looking for a tool that will tell/resolve for every function all the call paths (call it "routes") to it. For example: void deeper(int *pNumber) { *pNumber++; } void gateA(int *pNumber) { deeper(pNumber); } void gateB(int *pNumber) { gateA(pNumber); } void main() { int x = 123; gateA(&x); gateB(&x); } See? I need a tool that will tell me all the routes to deeper(), and more if possible. By saying "more" I mean that it will tell me if the pointer is the same as been provided to the calling function. This will greatly save me time. Thanks!

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  • Help with implementing a function to change size of dynamic array

    - by iRobot
    I'm trying to write a function that will change the size of a dynamic array to a new size. In my header file, I have: Image **images; //pointer to a dynamic array of image pointers int maximum; //size I want to do this by allocating a new array and copying the values over without changing their indices. If there are non-null pointers outside the range newmax, then we cant do this. So heres what I have: There are no compilation or runtime errors. However, I find that the new array isnt getting sized right. When I run the following test case: I should get an index out of bounds error, but instead the system lets it slide. Can anyone see the mistake? I've looked for hours but cant find anything.

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  • Can I reproduce Scala's behavior for == ?

    - by JPP
    In Programming in Scala, I can read that the == operator behaves as if it was defined like this: final def == (that: Any): Boolean = if (null eq this) {null eq that} else {this equals that} But there must actually be compiler magic to avoid null pointer exceptions, right? Is there any way for me to replicate this behavior with pure Scala; i.e., have an operator/method return one thing if the receiver is null and another one if it isn't? What I mean is an actual implementation of null eq this. I suppose I can write a "pimp" and then define the method on the wrapper class, but is there a more direct way to do this?

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  • .NET Regex - need matching string for parsing...

    - by TomTom
    Hello, I am a regex idiot and never found a good tutorial (links welcome, as well as a pointer to an interactive VS2010 integrated editor). I need to parse strings in the following form: [a/b]:c/d a, b: double with "." as possible separator. CAN be empty c: double with "." as separator d: integer, positive I.e. valid strings are: [/]:0.25/2 [-0.5/0.5]:0.05/2 [/0.1]:0.05/2 ;) Anyone can help? Thanks

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  • C++ syntax of constructors " 'Object1 a (1, Object1(2))''

    - by osgx
    Hello I have a such syntax in program class Object1 : BaseClass { BaseClass *link; int i; public: Object1(int a){i=a;} Object1(int a, Object1 /*place1*/ o) {i=a; link= &o;} }; int main(){ Object1 a(1, /*place2*/ Object1(2)); ... } What do I need in place1? I want to save a link (pointer) to the second object in the first object. Should I use in place1 reference "&"? What type will have "Object1(2)" in place2? Is it a constructor of the anonymous object? Will it have a "auto" storage type?

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  • between syntax, are there any equal function

    - by gcc
    /* char **mainp=malloc(sizeof(char *)*2); mainp[0]=malloc(sizeof(char)*300); mainp[1]=malloc(sizeof(char )*300); */ *I have some input about propositional calculus *After calculating some math funtion-removing paranthesis-changing"&" with ","-replacing "|" with"," I have >> (1) P,-Q,Q,-R is stored in mainp[0] R,A,P,B,F is stored in mainp[1] *My question is: Between comma , I have want to compare two pointer array. If there is any equal two or more functions(Q,-R is function representation) ,function which you will show me how to write must return int. According to example (1),function will return 1 (I expect like that) /*I have som thought://which function should I have use:*/ in for loop if( strspn(mainp[0][i])==1 ) increment d; continue; or in for loop srtcmp(mainp[0][i],mainp[1]);

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  • c++ - FIFO implementation

    - by Narek
    While implementing a FIFO I have used the following structure: struct Node { T info_; Node* link_; Node(T info, Node* link=0): info_(info), link_(link) {} }; I think this a well known trick for lots of STL containers (for example for List). Is this a good practice? What it means for compiler when you say that Node has a member with a type of it's pointer? Is this a kind of infinite loop? And finally, if this is a bad practice, how I could implement a better FIFO.

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  • question abouut string sort

    - by davit-datuashvili
    i have question from programming pearls problem is following show how to use lomuto's partitioning scheme to sort varying length bit strings in time proportional to the sum oof their length and algorithm is following each record in x[0..n-1] has an integer length and pointer to the array bit[0..length-1] code void bsort(l,u,depth){ if (l>=u) return; for (int i=l;i<u;i++) if (x[i].length<depth) swap(i,l++); m=l; if (x[i].bit[depth] ==0) swap(i,m++); bsort(l,m-1,depth+1); bsort(m,u,depth+1); please help me i need following things 1. how this algorith works 2.how implement in java?

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  • Break the limit of threading, segmentation fault

    - by user353573
    use pthread_create to create limited number of threads running concurrently Successfully compile and run However, after adding function pointer array to run the function, Segmentation fault Where is wrong? workserver number: 0 Segmentation fault void* workserver(void arg) { int status; while(true) { printf("workserver number: %d\n", (int)arg); ( job_queue[(int)arg])(); sleep(3); status = pthread_mutex_lock(&data.mutex); if(status != 0) printf("%d lock mutex", status); data.value = 1; status = pthread_cond_signal(&data.cond); if(status != 0) printf("%d signal condition", status); status = pthread_mutex_unlock(&data.mutex); if(status != 0) printf("%d unlock mutex", status); } }

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  • Method to register method to be called when event is raised

    - by zaidwaqi
    I have a Panel which contains 20 PictureBox controls. If a user clicks on any of the controls, I want a method within the Panel to be called. How do I do this? public class MyPanel : Panel { public MyPanel() { for(int i = 0; i < 20; i++) { Controls.Add(new PictureBox()); } } // DOESN'T WORK. // function to register functions to be called if the pictureboxes are clicked. public void RegisterFunction( <function pointer> func ) { foreach ( Control c in Controls ) { c.Click += new EventHandler( func ); } } } How do I implement RegisterFunction()? Also, if there are cool C# features that can make the code more elegant, please share.

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  • Are unspecified and undefined behavior required to be consistent between compiles?

    - by sharptooth
    Let's pretend my program contains a specific construct the C++ Standard states to be unspecified behavior. This basically means the implementation has to do something reasonable but is allowed not to document it. But is the implementation required to produce the same behavior every time it compiles a specific construct with unspecified behavior or is it allowed to produce different behavior in different compiles? What about undefined behavior? Let's pretend my program contains a construct that is UB according to the Standard. The implementation is allowed to exhibit any behavior. But can this behavior differ between compiles of the same program on the same compiler with same settings in the same environment? In other words, if I dereference a null pointer on line 78 in file X.cpp and the implementation formats the drive in such case does it mean that it will do the same after the program is recompiled?

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  • Abstract class and operator!= in c++

    - by Alessandro Teruzzi
    Hi All, I have problem implementing the operator!= in a set class deriving from an abstact one. The code looks like this: class Abstract { public: //to make the syntax easier let's use a raw pointer virtual bool operator!=(const Abstract* other) = 0; }; class Implementation { SomeObject impl_; //that already implement the operator!= public: bool operator!=(const Abstract* other) { return dynamic_cast<Implementation*>(other)->impl_ != this->impl_; } }; This code works but it has the drawback to use dynamic_cast and I need to handle error in casting operation. This is a generic problem that occur when a function of a concrete class it is trying to using some internal information (not available at the abstract class level) to perform a task. Is there any better way to solve this kind of problem? Cheers

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  • referencing struct fields in c with square brackets and an index instead of . and ->?

    - by lsiebert
    Assuming I have a structure such as: typedef struct { char * string1; char * string2; } TWO_WORDS; such that all the fields are of the same type, and my main has TWO_WORDS tw; can I reference string1 with tw[0] and string2 with two[1]? If so: is this part of the c standard? do i have to cast the struct to an array first? what about fields which are different sizes in memory what about fields which are different types but the same size? can you do pointer arithmetic within a structure? -

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  • C++ Inheritance Question

    - by shaz
    I have a base class MessageHandler and 2 derived classes, MessageHandler_CB and MessageHandler_DQ. The derived classes redefine the handleMessage(...) method. MH_DQ processes a message and puts the result in a deque while MH_CB processes the message and then executes a callback function. The base class has a static callback function that I pass along with a this pointer to a library which calls the static callback when a new message is available for processing. My problem comes when I am in the static callback with a void * pointing to either a MH_DQ or a MH_CB. If I cast it to the base class the empty MessageHandler::handleMessage(...) method is called, rather than the version in the appropriate derived class. What is the best way to address this situation from a design perspective and/or what language features might help me to implement a solution to my problem? Thanks in advance!

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  • How to do hex8 encoding in c?

    - by Tech163
    I am trying to encode a string in hex8 using c. The script I have right now is: int hex8 (char str) { str = printf("%x", str); if(strlen(str) == 1) { return printf("%s", "0", str); } else { return str; } } In this function, I will need to add a 0 ahead of the string if the length is less than 1. I don't know why I'm getting: passing argument 1 of 'strlen' makes pointer from integer without a cast Does anyone know why?

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  • memcpy does not copy the data

    - by user437777
    I am caught up with a weird problem. I have one build that copies data using memcpy, while another build does not. I don't understand why, because the relevant file is still the same. I am using following code: memcpy(pxCurrentInfo, &pxInfoBuffer->axgInfoBuffer[0], sizeof(tInfo)); Data in pxInfoBuffer is fine. When I check pxCurrentInfo they are all 0s. tInfo is a structure. To give a pointer, when I put the break point and change the value pxCurrentInfo->xDL.eMethod=0 it automatically updates/copies all the correct info from pxInfoBuffer->axgInfoBuffer[0], afterwards. I don't know why.

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  • How can Java assignment be made to point to an object instead of making a copy?

    - by Matthew Piziak
    In a class, I have: private Foo bar; public Constructor(Foo bar) { this.bar = bar; } Instead of creating a copy of bar from the object provided in the parameter, is it possible to include a pointer to bar in the constructor such that changing the original bar changes the field in this object? Another way of putting it: int x = 7; int y = x; x = 9; System.out.print(y); //Prints 7. It is possible to set it up so that printing y prints 9 instead of 7?

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  • C++, is it possible to obtain the dimension of an array?

    - by aaa
    hi. Suppose I have some pointer, which I want to reinterpret as static dimension array reference: double *p; double (&r)[4] = ?(p); // some construct? // clarify template< size_t N> void function(double (&a)[N]); ... double *p; function(p); // this will not work. // I would like to cast p as to make it appear as double[N] Is it possible to do so? how do I do it?

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  • lua function as argument in C

    - by Nil
    I'm going to pass a function to another function which should operate with the passed function. For example: handler(fun1("foo",2)) handler(fun2(1e-10)) The handler is something like calling the passed function many times. I'm going to bind handler, fun1, fun2 to C-functions. fun1 and fun2 are going to return some user data with a pointer to some cpp-class so that I can further recover which function was it. The problem now is that fun1 and fun2 are going to be called before passed to handler. But I don't need this, what I need is the kind of function and its parameters. However, I should be able to call fun1 and fun2 alone without handler: fun1("bar",3) fun2(1e-5) Is it possible to get the context the function is called from? While typing the question, I realized I could do following handler(fun1, "foo",2); handler(fun2, 1e-10);

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  • Why is this simple hello world code segfaulting?

    - by socks
    Excuse the beginner level of this question. I have the following simple code, but it does not seem to run. It gets a segmentation fault. If I replace the pointer with a simple call to the actual variable, it runs fine... I'm not sure why. struct node { int x; struct node *left; struct node *right; }; int main() { struct node *root; root->x = 42; printf("Hello world. %d", root->x); getchar(); return 0; } What is wrong with this code?

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  • Any efficient way to read datas from large binary file?

    - by limi
    Hi, I need to handle tens of Gigabytes data in one binary file. Each record in the data file is variable length. So the file is like: <len1><data1><len2><data2>..........<lenN><dataN> The data contains integer, pointer, double value and so on. I found python can not even handle this situation. There is no problem if I read the whole file in memory. It's fast. But it seems the struct package is not good at performance. It almost stuck on unpack the bytes. Any help is appreciated. Thanks.

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