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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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  • Convert NSString to string

    - by coure06
    NSDate *now = [NSDate date]; NSDateFormatter *formatter = [[NSDateFormatter alloc] init]; [formatter setDateFormat:@"yyyy"]; NSString *stringFromDate = [formatter stringFromDate:now]; CGContextShowTextAtPoint(context, 50, 50, stringFromDate, 5); I am not getting the exact date? also getting warning while compiling warning: passing argument 4 of 'CGContextShowTextAtPoint' from incompatible pointer type

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  • Send a variable on the heap to another thread

    - by user1201889
    I have a strange problem in C++. An address of a Boolean gets "destroyed" but it doesn't get touched. I know that there are beater way's to accomplish what I try to do, but I want to know what I do wrong. I have a main class; this main class contains a vector of another class. There is a strange problem when a new instance gets created of this object. This is how my code works: There will start a thread when the constructor gets called of the “2nd”object. This thread gets as Parameter a struct. This is the struct: struct KeyPressData { vector<bool> *AutoPressStatus; vector<int> *AutoPressTime; bool * Destroy; bool * Ready; }; The struct gets filled in the constructor: MultiBoxClient::MultiBoxClient() { //init data DestroyThread = new bool; ReadyThread = new bool; AutoThreadData = new KeyPressData; //Reseting data *DestroyThread = false; *ReadyThread = false; //KeyPressData configurating AutoThreadData->AutoPressStatus = &AutoPressStatus; AutoThreadData->AutoPressTime = &AutoPressTime; AutoThreadData->Destroy = DestroyThread; AutoThreadData->Ready = ReadyThread; //Start the keypress thread CreateThread(NULL,NULL,(LPTHREAD_START_ROUTINE)AutoKeyThread,AutoThreadData,NULL,NULL); } As long as the constructor is running will the program run fine. But when the constructor closes the address of the “AutoThreadData-Destroy” will get corrupted. The program will crash when I call the value of the pointer. void WINAPI AutoKeyThread(void * ThreadData) { KeyPressData * AutoThreadData = (KeyPressData*)ThreadData; while(true) { if(*AutoThreadData->Destroy == true) //CRASH { *AutoThreadData->Ready = true; return; } Sleep(100); } } What did I test: I logged the address of the AutoThreadData and the AutoThreadData-Destroy when the constrcutor is running and clossed; the AutoThreadData address is equal to AutoThreadData when the constructor is closed. So there is no problem here. The address of AutoThreadData-Destroy gets destroyed when the constructor is closed. But how can this happen? The Boolean is on the heap and the KeyPressData struct (AutoThreadData) is on the heap. Destroy before: 00A85328 Destroy after: FEEEFEEE Can someone maby explain why this crash? I know that I can send a pointer to my class to the thread. But I want to know what goes wrong here. That way I can learn from my mistakes. Could someone help me with this problem? Thanks!

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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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  • 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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  • In gzip libary, what's the difference between 'uncompress' and 'gzopen' ?

    - by Sol
    There are some functions to decompress in zlib library(zlib version 1.2.3) I want to decompress my source zip(.gz) file using 'uncompress' function. It is now working(error code -3) but gzopen is. It is still not working when I input payload pointer(passing gzip header) to 'uncompress' . So the question is "What's the valid arguments for uncompress function?" and If it needs different format, how can I make it? Google doesn't helpful this time :(

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  • 'Invalid conversion from some_type** to const some_type**'

    - by petersohn
    I've got a function that requires const some_type** as an argument (some_type is a struct, and the function needs a pointer to an array of this type). I declared a local variable of type some_type*, and initialized it. Then I call the function as f(&some_array), and the compiler (gcc) says: error: invalid conversion from ‘some_type**’ to ‘const some_type**’ What's the problem here? Why can't I convert a variable to const?

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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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  • 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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  • Login screen delay in CentOS 5.4 x64

    - by user208728
    I was happily running my CentOS 5.4 before something bad happened that somehow corrupted the 'nautilus' package. It stopped me from using the default Gnome Desktop. Then I installed (using yum) the KDE and nautilus later on. Now, KDE is running perfectly with one exception that it takes around 10 minutes before showing up the Login Screen and only a blue screen with mouse pointer keeps showing during those 10 minutes. Thanks in Anticipation. Regards, Talal

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  • How do you return a string from a function correctly in Dynamic C?

    - by aquanar
    I have a program I am trying to debug, but Dynamic C apparently treats strings differently than normal C does (well, character arrays, anyway). I have a function that I made to make an 8 character long (well, 10 to include the \0 ) string of 0s and 1s to show me the contents of an 8-bit char variable. (IE, I give it the number 13, it returns the string "0001101\0" ) When I use the code below, it prints out !{happy face] 6 times (well, the second one is the happy face alone for some reason), each return comes back as 0xDEAE or "!\x02. I thought it would dereference it and return the appropriate string, but it appears to just be sending the pointer and attempting to parse it. This may seem silly, but my experience was actually in C++ and Java, so going back to C brings up a few issues that were dealt with in later programming languages that I'm not entirely sure how to deal with (like the lack of string variables). How could I fix this code, or how would be a better way to do what I am trying to do (I thought maybe sending in a pointer to a character array and working on it from the function might work, but I thought I should ask to see if maybe I'm just trying to reinvent the wheel). Currently I have it set up like this: this is an excerpt from the main() display[0] = '\0'; for(i=0;i<6;i++) { sprintf(s, "%s ", *char_to_bits(buffer[i])); strcat(display, s); } DispStr(8,5, display); and this is the offending function: char *char_to_bits(char x) { char bits[16]; strcpy(bits,"00000000\0"); if (x & 0x01) bits[7]='1'; if (x & 0x02) bits[6]='1'; if (x & 0x04) bits[5]='1'; if (x & 0x08) bits[4]='1'; if (x & 0x10) bits[3]='1'; if (x & 0x20) bits[2]='1'; if (x & 0x40) bits[1]='1'; if (x & 0x80) bits[0]='1'; return bits; } and just for the sake of completion, the other function is used to output to the stdio window at a specific location: void DispStr(int x, int y, char *s) { x += 0x20; y += 0x20; printf ("\x1B=%c%c%s", x, y, s); }

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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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  • 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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  • 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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  • Problem getting size of Website Xcode

    - by Michael Amici
    When i try and compile I come up with a warning that reads initialization makes pointer from integer without a cast. No clue why. I am just trying to get the size of a website. #import "Lockerz_RedemptionViewController.h" @implementation Lockerz_RedemptionViewController -(IBAction)startLoop:(id) sender { NSData *dataNew = [NSData dataWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://www.google.com/"]]]; NSUInteger *len = [dataNew length]; //error is here NSLog(@"%@", len); }

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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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  • 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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  • 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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