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  • Why is a c++ reference considered safer than a pointer?

    - by anand.arumug
    When the c++ compiler generates very similar assembler code for a reference and pointer, why is using references preferred (and considered safer) compared to pointers? I did see Difference between pointer variable and reference variable in C++ which discusses the differences between them. EDIT-1: I was looking at the assembler code generated by g++ for this small program: int main(int argc, char* argv[]) { int a; int &ra = a; int *pa = &a; }

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  • How do i set CTRL not to show where the pointer is?

    - by Lewis Goddard
    After recently re-installing, i went through every System Setting and choose exactly how i wanted everthing to be. Except one thing. I'd never seen the Show Cursor on CTRL value before, and wanted to know what it was like. After a while it was simply annoying, whenever i paste of cut in chrome it takes the focus off of the text before i can press V. I have been through eveything in System Settings and can't find it again to disable it. How do i set CTRL not to pulse around the cursor? I will be happy with directions in System Settings, Ubuntu Tweak, or GConf.

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  • C++ function returning pointer, why does this work ? [migrated]

    - by nashmaniac
    So heres a simple c++ function what it does it take an array of characters as its argument and a integer n and then creates a new character array with only n elements of the array. char * cutString(char * ch , int n){ char * p = new char[n]; int i ; for(i = 0 ; i < n ; i++) p[i] = ch[i]; while(i <= n ){ p[i++] = '\0'; } return p ; } this works just fine but if I change char * p = new char[n]; to char p[n]; I see funny characters what happens ? What difference does the former make also p is a temporary variable then how does the function returns it alright ?

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  • How to get the actual address of a pointer in C?

    - by Airjoe
    BACKGROUND: I'm writing a single level cache simulator in C for a homework assignment, and I've been given code that I must work from. In our discussions of the cache, we were told that the way a small cache can hold large addresses is by splitting the large address into the position in the cache and an identifying tag. That is, if you had an 8 slot cache but wanted to store something with address larger than 8, you take the 3 (because 2^3=8) rightmost bits and put the data in that position; so if you had address 22 for example, binary 10110, you would take those 3 rightmost bits 110, which is decimal 5, and put it in slot 5 of the cache. You would also store in this position the tag, which is the remaining bits 10. One function, cache_load, takes a single argument, and integer pointer. So effectively, I'm being given this int* addr which is an actual address and points to some value. In order to store this value in the cache, I need to split the addr. However, the compiler doesn't like when I try to work with the pointer directly. So, for example, I try to get the position by doing: npos=addr%num_slots The compiler gets angry and gives me errors. I tried casting to an int, but this actually got me the value that the pointer was pointing to, not the numerical address itself. Any help is appreciated, thanks!

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  • Assign C++ instance method to a global-function-pointer ?

    - by umanga
    Greetings, My project structure is as follows: \- base (C static library) callbacks.h callbacks.c paint_node.c . . * libBase.a \-app (C++ application) main.cpp In C library 'base' , I have declared global-function-pointer as: in singleheader file callbacks.h #ifndef CALLBACKS_H_ #define CALLBACKS_H_ extern void (*putPixelCallBack)(); extern void (*putImageCallBack)(); #endif /* CALLBACKS_H_ */ in single C file they are initialized as callbacks.c #include "callbacks.h" void (*putPixelCallBack)(); void (*putImageCallBack)(); Other C files access this callback-functions as: paint_node.c #include "callbacks.h" void paint_node(node *node,int index){ //Call callbackfunction . . putPixelCallBack(node->x,node->y,index); } I compile these C files and generate a static library 'libBase.a' Then in C++ application, I want to assign C++ instance method to this global function-pointer: I did something like follows : in Sacm.cpp file #include "Sacm.h" extern void (*putPixelCallBack)(); extern void (*putImageCallBack)(); void Sacm::doDetection() { putPixelCallBack=(void(*)())&paintPixel; //call somefunctions in 'libBase' C library } void Sacm::paintPixel(int x,int y,int index) { qpainter.begin(this); qpainter.drawPoint(x,y); qpainter.end(); } But when compiling it gives the error: sacmtest.cpp: In member function ‘void Sacm::doDetection()’: sacmtest.cpp:113: error: ISO C++ forbids taking the address of an unqualified or parenthesized non-static member function to form a pointer to member function. Say ‘&Sacm::paintPixel’ sacmtest.cpp:113: error: converting from ‘void (Sacm::)(int, int, int)’ to ‘void ()()’ Any tips?

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  • How do I detect proximity of the mouse pointer to a line in Flex?

    - by Hanno Fietz
    I'm working on a charting UI in Flex. One of the features I want to implement is "snapping" of the mousepointer to the data points in the diagram. I. e., if the user hovers the mouse pointer over a line diagram and gets close to the data point, I want the pointer to move to the exact coordinates and show a marker, like this: Currently, the lines are drawn on a Shape, using the Graphics API. The Shape is a child DisplayObject of a custom UIComponent subclass with the exact same dimensions. This means, I already get mouseOver events on the parent of the diagram's canvas. Now I need a way to detect if the pointer is close to one of the data points. I. e. I need an answer to the question "Which data points lie within a radius of x pixels from my current position and which of them is closest?" upon each move of the mouse. I can think of the following possibilities: draw the lines not as simple lines in the graphics API, but as more advanced objects that can have their own mouseOver events. However, I want the snapping to trigger before the mouse is actually over the line. check the original data for possible candidates upon each mouse movement. Using binary search, I might be able to reduce the number of items I have to compare sufficently. prepare some kind of new data structure from the raw data that makes the above search more efficient. I don't know how that would look like. I'm guessing this is a pretty standard problem for a number of applications, but probably the actual code usually is inside of some framework. Is there anything I can read about this topic?

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  • Isn't an Iterator in c++ a kind of a pointer?

    - by Bilthon
    Ok this time I decided to make a list using the STL. I need to create a dedicated TCP socket for each client. So everytime I've got a connection, I instantiate a socket and add a pointer to it on a list. list<MyTcp*> SocketList; //This is the list of pointers to sockets list<MyTcp*>::iterator it; //An iterator to the list of pointers to TCP sockets. Putting a new pointer to a socket was easy, but now every time the connection ends I should disconnect the socket and delete the pointer so I don't get a huge memory leak, right? well.. I thought I was doing ok by setting this: it=SocketList.begin(); while( it != SocketList.end() ){ if((*it)->getClientId() == id){ pSocket = it; // <-------------- compiler complains at this line SocketList.remove(pSocket); pSocket->Disconnect(); delete pSocket; break; } } But the compiler is saying this: error: invalid cast from type ‘std::_List_iterator<MyTcp*>’ to type ‘MyTcp*’ Can someone help me here? i thought I was doing things right, isn't an iterator at any given time just pointing to one of the elements of the set? how can I fix it?

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  • How to change the location of pointer (mouse sonar) shortcut in windows?

    - by naxa
    Windows xp+ has a feature in control mouse to show location of pointer when i press the ctrl key. Is it possible to change this shortcut? Possible options (some are [not] mutually exclusive): built-in utility via registry via 3rd party tool or replacement (same feature, other utility) filename of the binary that defines/stores it (for a theoretical hack* ) *: disregarding windows file signatures and self-repair mechanisms for ease

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  • what is meant by normalization in huge pointers

    - by wrapperm
    Hi, I have a lot of confusion on understanding the difference between a "far" pointer and "huge" pointer, searched for it all over in google for a solution, couldnot find one. Can any one explain me the difference between the two. Also, what is the exact normalization concept related to huge pointers. Please donot give me the following or any similar answers: "The only difference between a far pointer and a huge pointer is that a huge pointer is normalized by the compiler. A normalized pointer is one that has as much of the address as possible in the segment, meaning that the offset is never larger than 15. A huge pointer is normalized only when pointer arithmetic is performed on it. It is not normalized when an assignment is made. You can cause it to be normalized without changing the value by incrementing and then decrementing it. The offset must be less than 16 because the segment can represent any value greater than or equal to 16 (e.g. Absolute address 0x17 in a normalized form would be 0001:0001. While a far pointer could address the absolute address 0x17 with 0000:0017, this is not a valid huge (normalized) pointer because the offset is greater than 0000F.). Huge pointers can also be incremented and decremented using arithmetic operators, but since they are normalized they will not wrap like far pointers." Here the normalization concept is not very well explained, or may be I'm unable to understand it very well. Can anyone try explaining this concept from a beginners point of view. Thanks, Rahamath

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  • define macro in C wont work

    - by Spidfire
    Im trying to make a macro in C that can tell if a char is a hex number ( 0-9 a-z A-Z) #define _hex(x) (((x) >= "0" && (x) <= "9" )||( (x) >= "a" && (x) <= "z") || ((x) >= "A" && (x) <= "Z") ? "true" : "false") this what ive come up with but it wont work with a loop like this char a; for(a = "a" ; a < "z";a++){ printf("%s => %s",a, _hex(a)); } but it gives a error test.c:8: warning: assignment makes integer from pointer without a cast test.c:8: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer

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  • Dell Alps Touchpad not working

    - by ppls
    I have a Dell 17R SE with Ubuntu 13.04. The touchpad is recognized as PS/2 mouse out of the box, giving just normal touchpad behaviour, but no tap to click, no scrolling, etc. Most answers related to that issue suggest trying an ALPS driver from dahetral.com: http://www.dahetral.com/public-download For installing I followed the steps on this page: https://www.linuxwind.org/html/dell-touchpad-driver-for-ubuntu-13-04.html Now my xinput looks like this: Virtual core pointer id=2 [master pointer (3)] ? ? Virtual core XTEST pointer id=4 [slave pointer (2)] ? ? PS/2 Mouse id=13 [slave pointer (2)] ? ? AlpsPS/2 ALPS GlidePoint id=14 [slave pointer (2)] ? ? Logitech Bluetooth Mouse M555b id=16 [slave pointer (2)] My touchpad isn't working at all now, just the two hardware buttons for left and right mouse buttons work. Interestingly also the tap to click functions works, but only in the address bar of nautilus, nowhere (!) else. What can I do? I would even switch back to initial state, where at least the basic touchpad functionality worked, i I knew, how to get there.

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  • Touchpad not working after connecting hdmi cable

    - by user286632
    I had installed Ubuntu 14.04 2 weeks back on my new laptop along side Windows 8. 1. And it was working fine. But yesterday after I connected Ubuntu with my TV using the HDMI cable, the cursor/ pointer stopped working. The pointer is not visible and my touchpad is not working. I connected the hdmi cable with youtube in Firefox. But only the wallpaper was visible on the TV. Also the right click menu, alt tab window, etc was also visible. But the side menu and the Firefox window was not visible. The pointer was visible on the tv and the touchpad was working, I was able to move the pointer. After I removed the HDMI cable, my cursor/pointer disappeared and my touchpad is not responding! ! I tried to restart many times, but still no luck. Its still not visible in the desktop. The pointer is visible in the login screen, but is not responding to the touchpad. I tried to login to my KDE session, there too the pointer is visible but is not responding to the touchpad. It is not moving.

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  • Is it a good object-oriented-design practice to send a pointer to private data to another class?

    - by Denis
    Hello everyone, There is well known recommendation not to include into class interface method that returns a pointer (or a reference) to private data of the class. But what do you think about public method of a class that sends to another class a pointer to the private data of the first one. For example: class A { public: void fA(void) {_b.fB(&_var)}; private: B _b; int _var; }; I think that it is some sort of data hiding damage: the private data define state of their own class, so why should one class delegate changes of its own state to another one? What do you think? Denis

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  • Safe to cast pointer to a forward-declared class to its true base class in C++?

    - by Matt DiMeo
    In one header file I have: #include "BaseClass.h" // a forward declaration of DerivedClass, which extends class BaseClass. class DerivedClass ; class Foo { DerivedClass *derived ; void someMethod() { // this is the cast I'm worried about. ((BaseClass*)derived)->baseClassMethod() ; } }; Now, DerivedClass is (in its own header file) derived from BaseClass, but the compiler doesn't know that at the time it's reading the definition above for class Foo. However, Foo refers to DerivedClass pointers and DerivedClass refers to Foo pointers, so they can't both know each other's declaration. First question is whether it's safe (according to C++ spec, not in any given compiler) to cast a derived class pointer to its base class pointer type in the absence of a full definition of the derived class. Second question is whether there's a better approach. I'm aware I could move someMethod()'s body out of the class definition, but in this case it's important that it be inlined (part of an actual, measured hotspot - I'm not guessing).

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  • Contents changed(cleared?) when access the pointer returned by std::string::c_str()

    - by justamask
    string conf()     {         vector v;         //..         v = func(); //this function returns a vector         return v[1];     }     void test()     {         const char* p = conf().c_str();         // the string object will be alive as a auto var         // so the pointer should be valid till the end of this function,right?           // ... lots of steps, but none of them would access the pointer p         // when access p here, SOMETIMES the contents would change ... Why?         // the platform is solaris 64 bit         // compiler is sun workshop 12         // my code is compiled as  ELF 32-bit MSB relocatable SPARC32PLUS Version 1, V8+ Required         // but need to link with some shared lib which are ELF 32-bit MSB dynamic lib SPARC Version 1, dynamically linked, stripped     }

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  • Is it good practice to avoid declaring a pointer to BOOL type in objective C?

    - by Krishnan
    I read this question in stackoverflow. The excerpt answer provided by bbum is below: The problem isn't the assignment, it is much more likely that you declared your instance variable to be BOOL *initialBroadcast;. There is no reason to declare the instance variable to be a pointer (at least not unless you really do need a C array of BOOLs).. Remove the * from the declaration. 1.Is there anything wrong in using a pointer variable even when I do not have to maintain an array of BOOLs? 2.I think even if avoiding them a good practice, it is not specific to objective-C and applies to all programming languages which has pointers. Please answer my questions.

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  • How do I reference a pointer from a different class?

    - by Justagruvn
    First off, I despise singletons with a passion. Though I should probably be trying to use one, I just don't want to. I want to create a data class (that is instantiated only once by a view controller on loading), and then using a different class, message the crap out of that data instance until it is brimming with so much data, it smiles. So, how do I do that? I made a pointer to the instance of the data class when I instantiated it. I'm now over in a separate view controller, action occurs, and I want to update the initial data object. I think I need to reference that object by way of pointer, but I have no idea how to do that. Yes, I've set properties and getters and setters, which seem to work, but only in the initial view controller class. Peace Love applesauce.

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  • C++ standard: dereferencing NULL pointer to get a reference?

    - by shoosh
    I'm wondering about what the C++ standard says about code like this: int* ptr = NULL; int& ref = *ptr; int* ptr2 = &ref; In practice the result is that ptr2 is NULL but I'm wondering, is this just an implementation detail or is this well defined in the standard? Under different circumstances a dereferencing of a NULL pointer should result in a crash but here I'm dereferencing it to get a reference which is implemented by the compiler as a pointer so there's really no actual dereferencing of NULL.

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  • Can I use a single pointer for my hash table in C?

    - by aks
    I want to implement a hash table in the following manner: struct list { char *string; struct list *next; }; struct hash_table { int size; /* the size of the table */ struct list **table; /* the table elements */ }; Instead of struct hash_table like above, can I use: struct hash_table { int size; /* the size of the table */ struct list *table; /* the table elements */ }; That is, can I just use a single pointer instead of a double pointer for the hash table elements? If yes, please explain the difference in the way the elements will be stored in the table?

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  • how to scroll IFrame without placing the mouse pointer on IE scrollbar?

    - by David
    I have this asp.net page as below. <body> <form id="form1" runat="server"> <div class="page" > <iframe id="iFrame1" style="width:100%" runat="server" height="1100" scrolling="yes" src="login.aspx" frameborder="0" align="left"> </iframe> </div> </form> </body> To scroll the iframe,I have to put the mouse pointer over the IE scroll bar. I just want to place the mouse pointer over the iframe and scroll the page.Please advice. thanks in advance.

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  • Why would my mouse pointer be jerky when it can't get a signal from my router?

    - by izb
    I've got a fairly new PC but when moving the mouse across the screen, the pointer jerks as if the PC is freezing momentarily every second or so. Strangely, this only seems to happen if the signal from the wifi router is bad. If I move the PC closer to the router to get a full signal, it's fine. It also seems to affect the keyboard; Opening notepad and holding down a key shows the same momentary freezes. -- Update: It's a logitech wireless mouse, and a wired USB logitech keyboard.

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