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  • What is the point of function pointers?

    - by gramm
    Hi, I have trouble seing the utility of the function pointers. I guess it may be useful in some cases (they exist, after all), but I can't think of a case where it's better or unavoidable to use a function pointer. Could you give some example of good use of function pointers (in C or C++)? Many thanks :)

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  • STL map - insert or update

    - by CodeJunkie
    I have a map of objects and I want to update the object mapped to a key, or create a new object and insert into the map. The update is done by a different function that takes a pointer to the object (void update(MyClass *obj)) What is the best way to "insert or update" an element in a map?

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  • Determining the word width in C

    - by das_weezul
    Hi! I'm learning C right now and so I'm fiddling about with pointers. Is there a way to determine the word width of the CPU in C because I'm writing a small program which prints it's own stack (Because I'm curious how it is structured), so that information would come in handy. Right now I'm using an int pointer, as an integer is 4 Bytes wide and I'm using a 32-bit Intel Atom CPU. Thanks in advance, C gurus ;o)

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  • Linux signals with extra information parameter

    - by Tester
    I was to have some extra information in the callback to sa_sigaction handler, it does not seems possible. So I was wondering if you could suggest me alternatives. Basic requirements: Function A raises an signal/event with a pointer to a struct Handler function tackles the event. The handler function would only be called on an event and a loop to wait for the event, as in select() , is undesirable. TIA

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  • What do people find difficult about C pointers?

    - by Paul
    From the number of questions posted here, it's clear that people have some pretty fundemental issues when getting their heads around pointers and pointer arithmetic. I'm curious to know why. They've never really caused me major problems (although I first learned about them back in the Neolithic). In order to write better answers to these questions, I'd like to know what people find difficult. So, if you're struggling with pointers, or you recently were but suddenly "got it", what were the aspects of pointers that caused you problems?

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  • LInux C++: how do profile time wasted due to cache misses?

    - by anon
    I know that I can use gprof to benchmark my code. However, I have this problem -- I have a smart pointer that has an extra level of indirection (think of it as a proxy object). As a result, I have this extra layer that effects pretty much all functions, and screws with caching. Is there a way to measure the time my CPU wastes due to cache misses? Thanks!

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  • Scan Numbers among letters in a Sentence

    - by ZaZu
    Hello, I have a pretty easy question. (using C) In a sentence such as In this document, there are 345 words and 6 figures How can I scan 345 and 6 while ignoring all that is in between ? I tried fscanf(FILE *pointer,"%d %d",&words,&figs); But it only gets the first value ... What am I doing wrong ?

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  • C++ variable alias - what's that exactly, and why is it better to turn if off?

    - by Poni
    I've read the essay Surviving the Release Version. Under the "Aliasing bugs" clause it says: You can get tighter code if you tell the compiler that it can assume no aliasing.... I've also read Aliasing (computing). What exactly is a variable alias? I understand it means using a pointer to a variable is an alias, but, how/why does it affect badly, or in other words - why telling the compiler that it can assume no aliasing would get me a "tighter code"

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  • unix DECLARE_WAIT_QUEUE_HEAD (var) var prototype?

    - by yoavstr
    hello i want to work with 2 queue in the module where i change my pointer to them therefore i need to use : //declartion wait_queue_head_t **currentQ; DECLARE_WAIT_QUEUE_HEAD (readWaitQ1); DECLARE_WAIT_QUEUE_HEAD (readWaitQ2); if(condition){ currentQ = &readWaitQ1; }else{ currentQ = &readWaitQ2; } but i get incorrect type for wake_up an other stuff using the queue. even thought i google it i couldnt find an answer can someone just give me the prototype needed?...

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  • managing IB objects without iboutlets

    - by palominoz
    i have got 24 buttons in my project.I need to manage them but I don't want to get my MainViewController polluted by 24 declarations of pointers, properties & synthesizes. i was thinking about using buttonPushed functions and do it like: -(IBAction)buttonPushed:(id)sender{ UIbutton *button=sender; [buttons addObjectAtIndex:[sender tag]]; } my question is:is sender a pointer to the IBObject?

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  • Sample code for POST + cookie?

    - by OverTheRainbow
    Hello, I've been googling for some VB.Net code to authenticate to a web server with the POST method, receive a session ID in a cookie, and then send this cookie along with all GET queries... but all I found is half-working code or C# code, ie. difficult to use for a VB.Net newbie. Would someone have some code handy or some pointer that I could use to get started? Thank you.

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  • C++ interview question

    - by benjamin button
    as i am not an expert in c++,i was not aware of the answer to this question asked in one of the interviews. lets say there is a base class pointer which is pointing to a base class object: baseclass *bptr; bptr= new baseclass; now if i do bptr= new derived; what is the problem here?

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  • problems with 'free' in C

    - by lego69
    hello, can somebody please explain can I free const char* ? I allocated new memory using malloc and when I'm trying to free it I always receive an error incompatible pointer type thanks in advance something like this char* name="Arnold"; const char* str=malloc(stlen(name)+1); free(str); <- here bug

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  • c++, when do you need/have to pass data as (*&)

    - by ra170
    I came across people passing data objects as: declaration: DataObject * data = 0; calling it as: SomeMethod( data ); definition of Somethod: void SomeMethod(SomeObject * & object) My obvious question is, when and why do you have to do this (& *)? Is it passing the pointer as reference?

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  • [C++ / NCURSES] Can't convert from 'int' to 'int *'

    - by flarn2006
    So I have these lines of code: int maxY, maxX; getmaxyx(stdscr, &maxY, &maxX); It gives me the following error: error C2440: '=' : cannot convert from 'int' to 'int *' Conversion from integral type to pointer type requires reinterpret_cast, C-style cast or function-style cast twice for each time I use it. I'm not even using the = operator! The curses.h file is included. What am I doing wrong?

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  • C++ Pass a hidden arg to a class constructor?

    - by JP
    I would like to define a class that accept the pointer to it's parent class as an Argument, but would it be possible to somehow pass it without needing to pass it directly such as: class Child { public: Child(Parent* hiddenArg); }; class Parent { public: Child myChild; }; I know this is weird, but I am making my own Signal/Slot implementation and Child would be a signal defined, but I would like to get the parent so I can use it's Event Dispatcher...

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  • Using two threads and controlling one from the other in java?

    - by sidra
    Can someone please help me out. I need to use two threads in a way that one thread will run permanently while(true) and will keep track of a positioning pointer (some random value coming in form a method). This thread has a logic, if the value equals something, it should start the new thread. And if the value does not equal it should stop the other thread. Can someone give me some code snippet (block level) about how to realize this?

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  • merging indexed array in Python

    - by leon
    Suppose that I have two numpy arrays of the form x = [[1,2] [2,4] [3,6] [4,NaN] [5,10]] y = [[0,-5] [1,0] [2,5] [5,20] [6,25]] is there an efficient way to merge them such that I have xmy = [[0, NaN, -5 ] [1, 2, 0 ] [2, 4, 5 ] [3, 6, NaN] [4, NaN, NaN] [5, 10, 20 ] [6, NaN, 25 ] I can implement a simple function using search to find the index but this is not elegant and potentially inefficient for a lot of arrays and large dimensions. Any pointer is appreciated.

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