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• How can a FILE* (pointer to a struct) be tested (if == NULL)?

  - by m4design

  I was playing around with C, anyways I was thinking how can file pointer (which points to a struct type), be tested if NULL as for instant: FILE *cfPtr; if ( ( cfPtr = fopen( "file.dat", "w" ) ) == NULL ) I tried to do that myself, but an error occurs. struct foo{ int x; }; struct foo bar = {0}; if (bar == NULL) puts("Yay\n"); else puts("Nay"); error C2088: '==' : illegal for struct Here's the FILE deceleration in the stdio.h file: struct _iobuf { char *_ptr; int _cnt; char *_base; int _flag; int _file; int _charbuf; int _bufsiz; char *_tmpfname; }; typedef struct _iobuf FILE;

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• How can I assign pointer member with long string?

  - by Nano HE

  Hi, When I did the practice below to erase my pointer member and assign new value to it. (*pMyPointer).member.erase(); (*pMyPointer).member.assign("Hello"); // Successfully Than I tried more... (*pMyPointer).member.erase(); (*pMyPointer).member.assign("Long Multi Lines Format String"); // How to? If the long multi lines string can't quote by double quoter, how to handle it. Thank you.

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• Why doesn't C++ allow you to request a pointer to the most derived class?

  - by Matthew Lowe

  (This question should probably be answered with a reference to Stroustrup.) It seems extremely useful to be able to request a pointer to the most derived class, as in the following: class Base { ... }; class DerivedA { ... }; class DerivedB { ... }; class Processor { public: void Do(Base* b) {...} void Do(DerivedA* d) {...} void Do(DerivedB* d) {...} }; list<Base*> things; Processor p; for(list<Base*>::iterator i=things.begin(), e=things.end(); i!=e; ++i) { p.Do(CAST_TO_MOST_DERIVED_CLASS(*i)); } But this mechanism isn't provided in c++. Why?

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• How to move file pointer to a particular location using fseek()?

  - by Noge

  My intention is to read every elements in the 2nd column into a buffer[] from the following .txt file: 9992891234 09.920 15.771 11.909 9992345971 07.892 12.234 09.234 9992348971 64.567 70.456 50.987 9992348231 89.234 85.890 58.982 I have know of a way to do it by using fscanf(): for (int i=0;i<4;i++) { fscanf(pFile, "%lld", &junk); fscanf(pFile, "%f", &buffer[i]); fscanf(pFile, "%f", &junk); fscanf(pFile, "%f", &junk); } However, since I'm doing parallel programing which requires me to use different Windows Threads to read different columns, so I'll need to read the elements in the 2nd column directly using fseek(). The question here is, what should I put in the 2nd argument in fseek() in the code below to move my file pointer to read the 2nd element of the 2nd line? fscanf(pFile, "%llf", &junk);//<------this is used to skip the 1st data for (int i=0;i<4;i++) { fscanf(pFile, "%f", &buffer[i]); fseek ( pFile , ??, SEEK_CUR );//<----how do I calculate this offset? }

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• How do I read UTF-8 characters via a pointer?

  - by Jen

  Suppose I have UTF-8 content stored in memory, how do I read the characters using a pointer? I presume I need to watch for the 8th bit indicating a multi-byte character, but how exactly do I turn the sequence into a valid Unicode character? Also, is wchar_t the proper type to store a single Unicode character? This is what I have in mind: wchar_t readNextChar (char** p) { char ch = *p++; if (ch & 128) { // This is a multi-byte character, what do I do now? // char chNext = *p++; // ... but how do I assemble the Unicode character? ... } ... }

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• How to declare a pointer to a variable as a parameter of a function in C++?

  - by Keand64

  I have a function that takes a pointer to a D3DXVECTOR3, but I have no reason to declare this beforehand. The most logical solution to me was using new: Function( //other parameters, new D3DXVECTOR3(x, y, 0)); but I don't know how I would go about deleting it, beign intitialized in a function. My next thought was to use the & operator, like so: Function( //other parameters, &D3DVECTOR3(x, y, 0)); but I don't know if this is a valid way to go about doing this. (It doesn't get an error, but neither does int *x; x = 50;). So should I use new, &, or some other technique I'm overlooking?

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• How is the implicit segment register of a near pointer determined?

  - by Daniel Trebbien

  In section 4.3 of Intel 64® and IA-32 Architectures Software Developer's Manual. Volume 1: Basic Architecture, it says: A near pointer is a 32-bit offset ... within a segment. Near pointers are used for all memory references in a flat memory model or for references in a segmented model where the identity of the segment being accessed is implied. This leads me to wondering: how is the implied segment register determined? I know that (%eip) and displaced (%eip) (e.g. -4(%eip)) addresses use %cs by default, and that (%esp) and displaced (%esp) addresses use %ss, but what about (%eax), (%edx), (%edi), (%ebp) etc., and can the implicit segment register depend also on the instruction that the memory address operand appears in?

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• How to use pointer from COM object on C#?

  - by Jaeh

  All. I'm trying to use my old dll file on .net project. So I converted this unmanaged COM object to managed one by using [tlbimp.exe] util from Windows SDK. However, one method returns a Object as a return value, but whenever I try to use it, my program generates an error. The weird thing is below: //Object[] item = s.GetObjects(); //this generates an type error Object item = s.GetObjects(); //this works okay System.WriteLine(items); //prints System.Object[] rather than System.Object. It seems like it returns a pointer which contains an object array. Isn't it ? Please anyone tell me how to handle this, and is there any documentation for this issue ?

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• How to fill a structure when a pointer to it, is passed as an argument to a function

  - by Ram

  I have a function: func (struct passwd* pw) { struct passwd* temp; struct passwd* save; temp = getpwnam("someuser"); /* since getpwnam returns a pointer to a static * data buffer, I am copying the returned struct * to a local struct. */ if(temp) { save = malloc(sizeof *save); if (save) { memcpy(save, temp, sizeof(struct passwd)); /* Here, I have to update passed pw* with this save struct. */ *pw = *save; /* (~ memcpy) */ } } } The function which calls func(pw) is able to get the updated information. But is it fine to use it as above. The statement *pw = *save is not a deep copy. I do not want to copy each and every member of structure one by one like pw-pw_shell = strdup(save-pw_shell) etc. Is there any better way to do it? Thanks.

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• C++ vector of strings, pointers to functions, and the resulting frustration.

  - by Kyle

  So I am a first year computer science student, for on of my final projects, I need to write a program that takes a vector of strings, and applies various functions to these. Unfortunately, I am really confused on how to use pointer to pass the vector from function to function. Below is some sample code to give an idea of what I am talking about. I also get an error message when I try to deference any pointer. thanks. #include <iostream> #include <cstdlib> #include <vector> #include <string> using namespace std; vector<string>::pointer function_1(vector<string>::pointer ptr); void function_2(vector<string>::pointer ptr); int main() { vector<string>::pointer ptr; vector<string> svector; ptr = &svector[0]; function_1(ptr); function_2(ptr); } vector<string>::pointer function_1(vector<string>::pointer ptr) { string line; for(int i = 0; i < 10; i++) { cout << "enter some input ! \n"; // i need to be able to pass a reference of the vector getline(cin, line); // through various functions, and have the results *ptr.pushback(line); // reflectedin main(). But I cannot use member functions } // of vector with a deferenced pointer. return(ptr); } void function_2(vector<string>::pointer ptr) { for(int i = 0; i < 10; i++) { cout << *ptr[i] << endl; } }

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• Configuring Multi-Tap on Synaptics Touchpad

  - by nunos

  I am having a hard time configuring my notebook's touchpad. The touchpad already works. It successfully responds to one-finger tap, two-finger tap and two-finger vertical scrolling. What I want to accomplish: change two-finger tap action from right-mouse click to middle-mouse click add three-finger tap functionality to yield right-mouse click action (i have checked that the three-finger tap is supported by my laptop's touchpad since it works on Windows) I read on a forum to use this as a guide. I have successfully accomplished point 1 with synclient TapButton2=2. However, I have to do it everytime I log in. I have tried to put that command on /etc/rc.local but the computer always boots and logins with the default configuration. Regarding point 2, I have tried synclient TapButton3=3 but it doesn't do anything when I three-finger tap the touchpad. I am running Ubuntu 11.10 on an Asus N82JV. /etc/X11/xorg.conf: nuno@mozart:~$ cat /etc/X11/xorg.conf Section "InputClass" Identifier "touchpad catchall" Driver "synaptics" MatchIsTouchpad "on" MatchDevicePath "/dev/input/event*" Option "TapButton1" "1" Option "TapButton2" "2" Option "TapButton3" "3" EndSection /usr/share/X11/xorg.conf.d/50-synaptics.conf: nuno@mozart:~$ cat /usr/share/X11/xorg.conf.d/50-synaptics.conf # Example xorg.conf.d snippet that assigns the touchpad driver # to all touchpads. See xorg.conf.d(5) for more information on # InputClass. # DO NOT EDIT THIS FILE, your distribution will likely overwrite # it when updating. Copy (and rename) this file into # /etc/X11/xorg.conf.d first. # Additional options may be added in the form of # Option "OptionName" "value" # Section "InputClass" Identifier "touchpad catchall" Driver "synaptics" MatchIsTouchpad "on" MatchDevicePath "/dev/input/event*" Option "TapButton1" "1" Option "TapButton2" "2" Option "TapButton3" "3" EndSection xinput list: nuno@mozart:~$ xinput list ? Virtual core pointer id=2 [master pointer (3)] ? ? Virtual core XTEST pointer id=4 [slave pointer (2)] ? ? Microsoft Microsoft® Nano Transceiver v2.0 id=12 [slave pointer (2)] ? ? Microsoft Microsoft® Nano Transceiver v2.0 id=13 [slave pointer (2)] ? ? ETPS/2 Elantech Touchpad id=16 [slave pointer (2)] ? Virtual core keyboard id=3 [master keyboard (2)] ? Virtual core XTEST keyboard id=5 [slave keyboard (3)] ? Power Button id=6 [slave keyboard (3)] ? Video Bus id=7 [slave keyboard (3)] ? Video Bus id=8 [slave keyboard (3)] ? Sleep Button id=9 [slave keyboard (3)] ? USB2.0 2.0M UVC WebCam id=10 [slave keyboard (3)] ? Microsoft Microsoft® Nano Transceiver v2.0 id=11 [slave keyboard (3)] ? Asus Laptop extra buttons id=14 [slave keyboard (3)] ? AT Translated Set 2 keyboard id=15 [slave keyboard (3)]

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• Configuring Multi-Tap on Synpaptics Touchpad

  - by nunos

  I am having a hard time configuring my notebook's touchpad. The touchpad already works. It succesfully responds to one-finger tap, two-finger tap and two-finger vertical scrolling. What I want to accomplish: change two-finger tap action from right-mouse click to middle-mouse click add three-finger tap functionality to yield right-mouse click action I read on a forum to use this as a guide. I have succesfully accomplished point 1 with synclient TapButton2=2. However, I have to do it everytime I log in. I have tried to put that command on /etc/rc.local but the computer always boots and logins with the default configuration. Regarding point 2, I have tried synclient TapButton3=3 but it doesn't do anything when I three-finger tap the touchpad. I am running Ubuntu 11.10 on an Asus N82JV. /etc/X11/xorg.conf: nuno@mozart:~$ cat /etc/X11/xorg.conf Section "InputClass" Identifier "touchpad catchall" Driver "synaptics" MatchIsTouchpad "on" MatchDevicePath "/dev/input/event*" Option "TapButton1" "1" Option "TapButton2" "2" Option "TapButton3" "3" EndSection /usr/share/X11/xorg.conf.d/50-synaptics.conf: nuno@mozart:~$ cat /usr/share/X11/xorg.conf.d/50-synaptics.conf # Example xorg.conf.d snippet that assigns the touchpad driver # to all touchpads. See xorg.conf.d(5) for more information on # InputClass. # DO NOT EDIT THIS FILE, your distribution will likely overwrite # it when updating. Copy (and rename) this file into # /etc/X11/xorg.conf.d first. # Additional options may be added in the form of # Option "OptionName" "value" # Section "InputClass" Identifier "touchpad catchall" Driver "synaptics" MatchIsTouchpad "on" MatchDevicePath "/dev/input/event*" Option "TapButton1" "1" Option "TapButton2" "2" Option "TapButton3" "3" EndSection xinput list: nuno@mozart:~$ xinput list ? Virtual core pointer id=2 [master pointer (3)] ? ? Virtual core XTEST pointer id=4 [slave pointer (2)] ? ? Microsoft Microsoft® Nano Transceiver v2.0 id=12 [slave pointer (2)] ? ? Microsoft Microsoft® Nano Transceiver v2.0 id=13 [slave pointer (2)] ? ? ETPS/2 Elantech Touchpad id=16 [slave pointer (2)] ? Virtual core keyboard id=3 [master keyboard (2)] ? Virtual core XTEST keyboard id=5 [slave keyboard (3)] ? Power Button id=6 [slave keyboard (3)] ? Video Bus id=7 [slave keyboard (3)] ? Video Bus id=8 [slave keyboard (3)] ? Sleep Button id=9 [slave keyboard (3)] ? USB2.0 2.0M UVC WebCam id=10 [slave keyboard (3)] ? Microsoft Microsoft® Nano Transceiver v2.0 id=11 [slave keyboard (3)] ? Asus Laptop extra buttons id=14 [slave keyboard (3)] ? AT Translated Set 2 keyboard id=15 [slave keyboard (3)]

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• Configuring Touchpad Multi-Tap on Ubuntu 11.10

  - by nunos

  I am having a hard time configuring my notebook's touchpad. I can do everything I can in Windows with the exception of three-finger tap, which doesn't work, and the action of two-finger tap which is giving me the equivalent to a right-mouse click, when I wanted a middle-mouse click. I read on a forum to use this as a guide. The problem is that I can't even find the configuration file /etc/X11/xorg.conf.d/10-synaptics.conf. I tried running pacman -S xf86-input-synaptics but I don't have the pacman program installed. When I try to install it by sudo apt-get install I get a pacman game instead! I know the guide is for archlinux, so maybe that's why it doesn't work with me. I am running Ubuntu 11.10 on an Asus N82JV. Any help on this is appreciated. Here's the output of xinput list: nuno@mozart:~$ xinput list ? Virtual core pointer id=2 [master pointer (3)] ? ? Virtual core XTEST pointer id=4 [slave pointer (2)] ? ? Microsoft Microsoft® Nano Transceiver v2.0 id=12 [slave pointer (2)] ? ? Microsoft Microsoft® Nano Transceiver v2.0 id=13 [slave pointer (2)] ? ? ETPS/2 Elantech Touchpad id=16 [slave pointer (2)] ? Virtual core keyboard id=3 [master keyboard (2)] ? Virtual core XTEST keyboard id=5 [slave keyboard (3)] ? Power Button id=6 [slave keyboard (3)] ? Video Bus id=7 [slave keyboard (3)] ? Video Bus id=8 [slave keyboard (3)] ? Sleep Button id=9 [slave keyboard (3)] ? USB2.0 2.0M UVC WebCam id=10 [slave keyboard (3)] ? Microsoft Microsoft® Nano Transceiver v2.0 id=11 [slave keyboard (3)] ? Asus Laptop extra buttons id=14 [slave keyboard (3)] ? AT Translated Set 2 keyboard id=15 [slave keyboard (3)]

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• How can I change mouse keymapping

  - by zuberuber

  I have Razer DeathAdder(left handed edition) and A4Tech wireless mouse. My problem is I don't know how to change wireless mouse keymapping(swaping left/right click). Can somebody guide me how to do such thing? List of my devices: ? Virtual core pointer id=2 [master pointer (3)] ? ? Virtual core XTEST pointer id=4 [slave pointer (2)] ? ? Logitech Unifying Device. Wireless PID:4004 id=8 [slave pointer (2)] ? ? Razer Razer DeathAdder id=11 [slave pointer (2)] ? ? A4TECH USB Device id=12 [slave pointer (2)] ? ? A4TECH USB Device id=13 [slave pointer (2)] ? Virtual core keyboard id=3 [master keyboard (2)] ? Virtual core XTEST keyboard id=5 [slave keyboard (3)] ? Power Button id=6 [slave keyboard (3)] ? Power Button id=7 [slave keyboard (3)] ? Logitech USB Keyboard id=9 [slave keyboard (3)] ? Logitech USB Keyboard id=10 [slave keyboard (3)] This is my Razer xinput: Device 'Razer Razer DeathAdder': Device Enabled (121): 1 Coordinate Transformation Matrix (123): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000 Device Accel Profile (246): 0 Device Accel Constant Deceleration (247): 5.000000 Device Accel Adaptive Deceleration (248): 1.000000 Device Accel Velocity Scaling (249): 10.000000 Device Product ID (240): 5426, 22 Device Node (241): "/dev/input/event4" Evdev Axis Inversion (250): 0, 0 Evdev Axes Swap (252): 0 Axis Labels (253): "Rel X" (131), "Rel Y" (132), "Rel Vert Wheel" (274) Button Labels (254): "Button Left" (124), "Button Middle" (125), "Button Right" (126), "Button Wheel Up" (127), "Button Wheel Down" (128), "Button Horiz Wheel Left" (129), "Button Horiz Wheel Right" (130), "Button Side" (269), "Button Extra" (270), "Button Forward" (271), "Button Back" (272), "Button Task" (273), "Button Unknown" (243), "Button Unknown" (243), "Button Unknown" (243), "Button Unknown" (243) Evdev Middle Button Emulation (255): 0 Evdev Middle Button Timeout (256): 50 Evdev Third Button Emulation (257): 0 Evdev Third Button Emulation Timeout (258): 1000 Evdev Third Button Emulation Button (259): 3 Evdev Third Button Emulation Threshold (260): 20 Evdev Wheel Emulation (261): 0 Evdev Wheel Emulation Axes (262): 0, 0, 4, 5 Evdev Wheel Emulation Inertia (263): 10 Evdev Wheel Emulation Timeout (264): 200 Evdev Wheel Emulation Button (265): 4 Evdev Drag Lock Buttons (266): 0 And this is my wireless mouse xinput: Device 'A4TECH USB Device': Device Enabled (121): 1 Coordinate Transformation Matrix (123): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000 Device Accel Profile (246): 0 Device Accel Constant Deceleration (247): 1.000000 Device Accel Adaptive Deceleration (248): 1.000000 Device Accel Velocity Scaling (249): 10.000000 Device Product ID (240): 2522, 1359 Device Node (241): "/dev/input/event16" Evdev Axis Inversion (250): 0, 0 Evdev Axes Swap (252): 0 Axis Labels (253): "Rel X" (131), "Rel Y" (132), "Rel Horiz Wheel" (245), "Rel Vert Wheel" (274) Button Labels (254): "Button Left" (124), "Button Middle" (125), "Button Right" (126), "Button Wheel Up" (127), "Button Wheel Down" (128), "Button Horiz Wheel Left" (129), "Button Horiz Wheel Right" (130), "Button Side" (269), "Button Extra" (270), "Button Forward" (271), "Button Back" (272), "Button Task" (273), "Button Unknown" (243), "Button Unknown" (243), "Button Unknown" (243), "Button Unknown" (243), "Button Unknown" (243), "Button Unknown" (243), "Button Unknown" (243), "Button Unknown" (243), "Button Unknown" (243), "Button Unknown" (243), "Button Unknown" (243), "Button Unknown" (243) Evdev Middle Button Emulation (255): 0 Evdev Middle Button Timeout (256): 50 Evdev Third Button Emulation (257): 0 Evdev Third Button Emulation Timeout (258): 1000 Evdev Third Button Emulation Button (259): 3 Evdev Third Button Emulation Threshold (260): 20 Evdev Wheel Emulation (261): 0 Evdev Wheel Emulation Axes (262): 0, 0, 4, 5 Evdev Wheel Emulation Inertia (263): 10 Evdev Wheel Emulation Timeout (264): 200 Evdev Wheel Emulation Button (265): 4 Evdev Drag Lock Buttons (266): 0

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• Emacs editor copy and deletion

  - by Null pointer

  I am a huge fan of emacs.. But even after 1 year of practising on emacs I am unable to solve these three annoying issues about emacs please help me! 1.Whenever I want to copy the content from emacs into other things such as a website textarea I have to use GUI copy button because ctrl+w doesn't work. Is there any way to do this from emacs-command line. 2.Whenever I delete something using ctrl+shft+SPC or ctrl+k etc I don't want it to be stored in kill ring how do I do it(I know ctrl+D does this but it deletes only one char at a time)? 3.Whenever I select text by mouse and press backspace then text goes into kill ring(Which I want to change as mentioned) but same doesn't happen when I select text with ctrl+SPC(set mark) and then ctrl+f/ctrl+b etc. Please help me! Thanks in Advanced!

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• Switching between Discrete and Integrated GPUs

  - by void-pointer

  Hello everyone, I develop CUDA applications on my Alienware M17x portable back-breaker, which has two discrete GTX 285M GPUs and one integrated GeForce 9400M GPU. I can currently switch between them using NVIDIA's software, but I would like the ability to do so within my applications for purposes of benchmarking and general convenience. Apparently this requires the "NDA version" of NVIDIA's Driver API, which I know not how to obtain. Would using this API be the only way to accomplish what I seek, and if so, how would I obtain it? A solution using Windows APIs would also be acceptable, though less preferable to one which would leverage a cross-platform API. I have created a similar thread concerning the matter on NVIDIA's forum, which is down at the time of this writing. Thanks for reading my question; it is much appreciated!

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• execute a shell script when USB is connected

  - by Null pointer

  I am working on an application which deals with all kinds of USB storage devices(such as taking backup, updating DataLogFile etc) My problem is : I want to write a shell script which is stored in this USB drive(As usb is at center of my project so USB is going to be same but PC's will change) AND this script should be executed as soon as the USB drive is connected to my Linux system.I will not need any kind of "root" or "sudo" permissions for other tasks which I am going to do in this shell script.

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• pointer being freed was not allocated. Complex malloc history help

  - by Martin KS

  I've followed the guides helpfully linked here: http://stackoverflow.com/questions/295778/iphone-debugging-pointer-being-freed-was-not-allocated-errors but the malloc_history is really throwing me for a loop, can anyone shed any light on the following: ALLOC 0x185c600-0x18605ff [size=16384]: thread_a068a4e0 |start | main | UIApplicationMain | -[UIApplication _run] | CFRunLoopRunInMode | CFRunLoopRunSpecific | PurpleEventCallback | _UIApplicationHandleEvent | -[UIApplication sendEvent:] | -[UIApplication handleEvent:withNewEvent:] | -[UIApplication _reportAppLaunchFinished] | CA::Transaction::commit() | CA::Context::commit_transaction(CA::Transaction*) | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CA::Context::commit_layer(_CALayer*, unsigned int, unsigned int, void*) | CA::Render::encode_set_object(CA::Render::Encoder*, unsigned long, unsigned int, CA::Render::Object*, unsigned int) | CA::Render::Layer::encode(CA::Render::Encoder*) const | CA::Render::Image::encode(CA::Render::Encoder*) const | CA::Render::Encoder::encode_data_async(void const*, unsigned long, void (*)(void const*, void*), void*) | CA::Render::Encoder::encode_bytes(void const*, unsigned long) | CA::Render::Encoder::grow(unsigned long) | realloc | malloc_zone_realloc ---- FREE 0x185c600-0x18605ff [size=16384]: thread_a068a4e0 |start | main | UIApplicationMain | -[UIApplication _run] | CFRunLoopRunInMode | CFRunLoopRunSpecific | PurpleEventCallback | _UIApplicationHandleEvent | -[UIApplication sendEvent:] | -[UIApplication handleEvent:withNewEvent:] | -[UIApplication _reportAppLaunchFinished] | CA::Transaction::commit() | CA::Context::commit_transaction(CA::Transaction*) | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CALayerCommitIfNeeded | CA::Context::commit_layer(_CALayer*, unsigned int, unsigned int, void*) | CA::Render::encode_set_object(CA::Render::Encoder*, unsigned long, unsigned int, CA::Render::Object*, unsigned int) | CA::Render::Layer::encode(CA::Render::Encoder*) const | CA::Render::Image::encode(CA::Render::Encoder*) const | CA::Render::Encoder::encode_data_async(void const*, unsigned long, void (*)(void const*, void*), void*) | CA::Render::Encoder::encode_bytes(void const*, unsigned long) | CA::Render::Encoder::grow(unsigned long) | realloc | malloc_zone_realloc ALLOC 0x185e000-0x185e62f [size=1584]: thread_a068a4e0 |start | main | UIApplicationMain | GSEventRun | GSEventRunModal | CFRunLoopRunInMode | CFRunLoopRunSpecific | __NSFireDelayedPerform | -[UITableView _userSelectRowAtIndexPath:] | -[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:] | -[PLAlbumView tableView:didSelectRowAtIndexPath:] | -[PLUIAlbumViewController albumView:selectedPhoto:] | PLNotifyImagePickerOfImageAvailability | -[UIImagePickerController _imagePickerDidCompleteWithInfo:] | -[GalleryViewController imagePickerController:didFinishPickingMediaWithInfo:] | UIImageJPEGRepresentation | CGImageDestinationFinalize | _CGImagePluginWriteJPEG | writeOne | _cg_jpeg_start_compress | _cg_jinit_compress_master | _cg_jinit_c_prep_controller | alloc_sarray | alloc_large | malloc | malloc_zone_malloc ---- FREE 0x185e000-0x185e62f [size=1584]: thread_a068a4e0 |start | main | UIApplicationMain | GSEventRun | GSEventRunModal | CFRunLoopRunInMode | CFRunLoopRunSpecific | __NSFireDelayedPerform | -[UITableView _userSelectRowAtIndexPath:] | -[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:] | -[PL AlbumView tableView:didSelectRowAtIndexPath:] | -[PLUIAlbumViewController albumView:selectedPhoto:] | PLNotifyImagePickerOfImageAvailability | -[UIImagePickerController _imagePickerDidCompleteWithInfo:] | -[GalleryViewController imagePickerController:didFinishPickingMediaWithInfo:] | UIImageJPEGRepresentation | CGImageDestinationFinalize | _CGImagePluginWriteJPEG | writeOne | _cg_jpeg_abort | free_pool | free ALLOC 0x185c800-0x185ea1f [size=8736]: thread_a068a4e0 |start | main | UIApplicationMain | GSEventRun | GSEventRunModal | CFRunLoopRunInMode | CFRunLoopRunSpecific | __NSFireDelayedPerform | -[UITableView _userSelectRowAtIndexPath:] | -[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:] | -[PLAlbumView tableView:didSelectRowAtIndexPath:] | -[PLUIAlbumViewController albumView:selectedPhoto:] | PLNotifyImagePickerOfImageAvailability | -[UIImagePickerController _imagePickerDidCompleteWithInfo:] | -[GalleryViewController imagePickerController:didFinishPickingMediaWithInfo:] | -[UIImage initWithData:] | _UIImageRefFromData | CGImageSourceCreateImageAtIndex | makeImagePlus | _CGImagePluginInitJPEG | initImageJPEG | calloc | malloc_zone_calloc

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• Is there a practical benefit to casting a NULL pointer to an object and calling one of its member fu

  - by zdawg

  Ok, so I know that technically this is undefined behavior, but nonetheless, I've seen this more than once in production code. And please correct me if I'm wrong, but I've also heard that some people use this "feature" as a somewhat legitimate substitute of a lacking aspect of the current C++ standard, namely, the inability to obtain the address (well, offset really) of a member function. For example, this is out of a popular implementation of a PCRE (Perl-compatible Regular Expression) library: #ifndef offsetof #define offsetof(p_type,field) ((size_t)&(((p_type *)0)->field)) #endif One can debate whether the exploitation of such a language subtlety in a case like this is valid or not, or even necessary, but I've also seen it used like this: struct Result { void stat() { if(this) // do something... else // do something else... } }; // ...somewhere else in the code... ((Result*)0)->stat(); This works just fine! It avoids a null pointer dereference by testing for the existence of this, and it does not try to access class members in the else block. So long as these guards are in place, it's legitimate code, right? So the question remains: Is there a practical use case, where one would benefit from using such a construct? I'm especially concerned about the second case, since the first case is more of a workaround for a language limitation. Or is it? PS. Sorry about the C-style casts, unfortunately people still prefer to type less if they can.

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• C++ Changing a class in a dll where a pointer to that class is returned to other dlls...

  - by Patrick

  Hello, Horrible title I know, horrible question too. I'm working with a bit of software where a dll returns a ptr to an internal class. Other dlls (calling dlls) then use this pointer to call methods of that class directly: //dll 1 internalclass m_class; internalclass* getInternalObject() { return &m_class; } //dll 2 internalclass* classptr = getInternalObject(); classptr->method(); This smells pretty bad to me but it's what I've got... I want to add a new method to internalclass as one of the calling dlls needs additional functionality. I'm certain that all dlls that access this class will need to be rebuilt after the new method is included but I can't work out the logic of why. My thinking is it's something to do with the already compiled calling dll having the physical address of each function within internalclass in the other dll but I don't really understand it; is anyone here able to provide a concise explanation of how the dlls (new internal class dll, rebuilt calling dll and calling dll built with previous version of the internal class dll) would fit together? Thanks, Patrick

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• Should we point to an NSManagedObject entity with weak instead of strong pointer?

  - by Jim Thio

  I think because NSManagedObject is managed by the managedObject context the pointer should be weak. Yet it often goes back to 0 in my cases. for (CategoryNearby * CN in sorted) { //[arrayOfItems addObject:[NSString stringWithFormat:@"%@ - %d",CN.name,[CN.order intValue]]]; NearbyShortcutTVC * tvc=[[NearbyShortcutTVC alloc]init]; tvc.categoryNearby =CN; // tvc.titleString=[NSString stringWithFormat:@"%@",CN.name]; // tvc.displayed=CN.displayed; [arrayOfItemsLocal addObject:tvc]; //CN PO(tvc); PO(tvc.categoryNearby); while (false); } self.arrayOfItems = arrayOfItemsLocal; PO(self.categoriesNearbyInArrayOfItems); [self.tableViewa reloadData]; ... Yet somewhere down the line: tvc.categoryNearby becomes nil. I do not know how or when or where it become nil. How do I debug this? Or should the reference be strong instead? This is the interface of NearbyShortcutTVC by the way @interface NearbyShortcutTVC : BGBaseTableViewCell{ } @property (weak, nonatomic) CategoryNearby * categoryNearby; @end To make sure that we're talking about the same object I print all the memory addresses of the NSArray They're both the exact same object. But somehow the categoryNearby property of the object is magically set to null somewhere. self.categoriesNearbyInArrayOfItems: ( 0x883bfe0, 0x8b6d420, 0x8b6f9f0, 0x8b71de0, 0xb073f90, 0xb061a10, 0xb06a880, 0x8b74940, 0x8b77110, 0x8b794e0, 0x8b7bf40, 0x8b7cef0, 0x8b7f4b0, 0x8b81a30, 0x88622d0, 0x8864e60, 0xb05c9a0 ) self.categoriesNearbyInArrayOfItems: ( 0x883bfe0, 0x8b6d420, 0x8b6f9f0, 0x8b71de0, 0xb073f90, 0xb061a10, 0xb06a880, 0x8b74940, 0x8b77110, 0x8b794e0, 0x8b7bf40, 0x8b7cef0, 0x8b7f4b0, 0x8b81a30, 0x88622d0, 0x8864e60, 0xb05c9a0 )

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• Casting/dereferencing member variable pointer from void*, is this safe?

  - by Damien

  Hi all, I had a problem while hacking a bigger project so I made a simpel test case. If I'm not omitting something, my test code works fine, but maybe it works accidentally so I wanted to show it to you and ask if there are any pitfalls in this approach. I have an OutObj which has a member variable (pointer) InObj. InObj has a member function. I send the address of this member variable object (InObj) to a callback function as void*. The type of this object never changes so inside the callback I recast to its original type and call the aFunc member function in it. In this exampel it works as expected, but in the project I'm working on it doesn't. So I might be omitting something or maybe there is a pitfall here and this works accidentally. Any comments? Thanks a lot in advance. (The problem I have in my original code is that InObj.data is garbage). #include <stdio.h> class InObj { public: int data; InObj(int argData); void aFunc() { printf("Inside aFunc! data is: %d\n", data); }; }; InObj::InObj(int argData) { data = argData; } class OutObj { public: InObj* objPtr; OutObj(int data); ~OutObj(); }; OutObj::OutObj(int data) { objPtr = new InObj(data); } OutObj::~OutObj() { delete objPtr; } void callback(void* context) { ((InObj*)context)->aFunc(); } int main () { OutObj a(42); callback((void*)a.objPtr); }

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• I just don't get the C++ Pointer/Reference system.

  - by gnm

  I've never had problems with references as in Python (implicit) or PHP (explicit &). In PHP you write $p = &$myvar; and you have $p as a reference pointing to $myVar. So I know in C++ you can do this: void setToSomething( int& var ) { var = 123; } int myInt; setToSomething( myInt ); Myint is now 123, why? Doesn't & mean "memory address of" x in C++? What do I do then if var is only the adress to myInt and not a pointer? void setToSomething( int* var ) { var* = 123; } int myInt; int* myIntPtr = &myInt; setToSomething( myIntPtr ); Does the above work as expected? I don't understand the difference between * and & in C++ fully. They tell you & is used to get the adress of a variable, but why IN GODS NAME does that help you in functions etc. like in the first example?

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• How do I reset my pointer to a specific array location?

  - by ohtanya

  I am a brand new programming student, so please forgive my ignorance. My assignment states: Write a program that declares an array of 10 integers. Write a loop that accepts 10 values from the keyboard and write another loop that displays the 10 values. Do not use any subscripts within the two loops; use pointers only. Here is my code: #include "stdafx.h" #include <iostream> using namespace std; int main() { const int NUM = 10; int values[NUM]; int *p = &values[0]; int x; for(x = 0; x < NUM; ++x, ++p) { cout << "Enter a value: "; cin >> *p; } for(x = 0; x < NUM; ++x, ++p) { cout << *p << " "; } return 0; } I think I know where my problem is. After my first loop, my pointer is at values[10], but I need to get it back to values[0] to display them. How can I do that?

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• Pointer to 2D array. Why does this example work?

  - by Louise

  I have this code example, but I don't understand why changing the values in the array inside outputUsingArray() are changing the original array. I would have expected changing the values of the array in outputUsingArray() would only be for a local copy of the array. Why isn't that so? However, this is the behaviour I would like, but I don't understand why it work. #include <stdlib.h> #include <stdio.h> void outputUsingArray(int array[][4], int n_rows, int n_cols) { int i, j; printf("Output Using array\n"); for (i = 0; i < n_rows; i++) { for (j = 0; j < n_cols; j++) { // Either can be used. //printf("%2d ", array[i][j] ); printf("%2d ", *(*(array+i)+j)); } printf("\n"); } printf("\n"); array[0][0] = 100; array[2][3] = 200; } void outputUsingPointer(int (*array)[4], int n_rows, int n_cols) { int i, j; printf("Output Using Pointer to Array i.e. int (*array)[4]\n"); for (i = 0; i < n_rows; i++) { for (j = 0; j < n_cols; j++) { printf("%2d ", *(*(array+i) + j )); } printf("\n"); } printf("\n"); } int main() { int array[3][4] = { { 0, 1, 2, 3 }, { 4, 5, 6, 7 }, { 8, 9, 10, 11 } }; outputUsingPointer((int (*)[4])array, 3, 4); outputUsingArray(array, 3, 4); printf("0,0: %i\n", array[0][0]); printf("2,3: %i\n", array[2][3]); return 0; }

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