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• STL deque accessing by index is O(1)?

  - by jasonline

  I've read that accessing elements by position index can be done in constant time in a STL deque. As far as I know, elements in a deque may be stored in several non-contiguous locations, eliminating safe access through pointer arithmetic. For example: abc-defghi-jkl-mnop The elements of the deque above consists of a single character. The set of characters in one group indicate it is allocated in contiguous memory (e.g. abc is in a single block of memory, defhi is located in another block of memory, etc.). Can anyone explain how accessing by position index can be done in constant time, especially if the element to be accessed is in the second block? Or does a deque have a pointer to the group of blocks? Update: Or is there any other common implementation for a deque?

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• In a binary search Tree

  - by user1044800

  In a binary search tree that takes a simple object.....when creating the getter and setter methods for the left, right, and parent. do I a do a null pointer? as in this=this or do I create the object in each method? Code bellow... This is my code: public void setParent(Person parent) { parent = new Person( parent.getName(), parent.getWeight()); //or is the parent supposed to be a null pointer ???? This is the code it came from: public void setParent(Node parent) { this.parent = parent; } Their code takes a node from the node class...my set parent is taking a person object from my person class.....

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• Problem with pointers and getstring function

  - by volting

  I am trying to write a function to get a string from the uart1. Its for an embedded system so I don't want to use malloc. The pointer that is passed to the getstring function seems to point to garbage after the gets_e_uart1() is called. I don't use pointers too often so I'm sure it is something really stupid and trivial that Im doing wrong. Regards, V int main() { char *ptr = 0; while(1) { gets_e_uart1(ptr, 100); puts_uart1(ptr); } return 0; }*end main*/ //------------------------------------------------------------------------- //gets a string and echos it //returns 0 if there is no error char getstring_e_uart1(char *stringPtr_, const int SIZE_) { char buffer_[SIZE_]; stringPtr_ = buffer_; int start_ = 0, end_ = SIZE_ - 1; char errorflag = 0; /*keep geting chars until newline char recieved*/ while((buffer_[start_++] = getchar_uart1())!= 0x0D) { putchar_uart1(buffer_[start_]);//echo it /*check for end of buffer wraparound if neccesary*/ if(start_ == end_) { start_ = 0; errorflag = 1; } } putchar_uart1('\n'); putchar_uart1('\r'); /*check for end of buffer wraparound if neccesary*/ if(start_ == end_) { buffer_[0] = '\0'; errorflag = 1; } else { buffer_[start_++] = '\0'; } return errorflag; } Update: I decided to go with approach of passing a pointer an array to the function. This works nicely, thanks to everyone for the informative answers. Updated Code: //------------------------------------------------------------------------- //argument 1 should be a pointer to an array, //and the second argument should be the size of the array //gets a string and echos it //returns 0 if there is no error char getstring_e_uart1(char *stringPtr_, const int SIZE_) { char *startPtr_ = stringPtr_; char *endPtr_ = startPtr_ + (SIZE_ - 1); char errorflag = 0; /*keep geting chars until newline char recieved*/ while((*stringPtr_ = getchar_uart1())!= 0x0D) { putchar_uart1(*stringPtr_);//echo it stringPtr_++; /*check for end of buffer wraparound if neccesary*/ if(stringPtr_ == endPtr_) { stringPtr_ = startPtr_; errorflag = 1; } } putchar_uart1('\n'); putchar_uart1('\r'); /*check for end of buffer wraparound if neccesary*/ if(stringPtr_ == endPtr_) { stringPtr_ = startPtr_; *stringPtr_ = '\0'; errorflag = 1; } else { *stringPtr_ = '\0'; } return errorflag; }

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• JNI AttachCurrentThread NULLs the jenv

  - by Damg

  Hello all, I'm currently in the process of adding JNI functionality into a legacy delphi app. In a single-threaded environment everything works fine, but as soon as I move into multi-threaded environment, things start to become hairy. My problem is that calling JavaVM^.AttachCurrentThread( JavaVM, @JEnv, nil ); returns 0, but puts the JEnv pointer to nil. I have no idea why jvm.dll should return a NULL pointer. Is there anything I am missing? Thank you in advance -- damg PS: * Environment: WinXP + JDK 1.6 * Using JNI.pas from http://www.pacifier.com/~mmead/jni/delphi/

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• Strange difference between optimized/non optimized microsoft c++ code

  - by Anders Forsgren

  I have a c++ program with a method that looks something like this: int myMethod(int* arr1, int* arr2, int* index) { arr1--; arr2--; int val = arr1[*index]; int val2 = arr2[val]; doMoreThings(val); } With optimizations enabled (/O2) the first line where the first pointer is decremented is not executed. I assume the compiler believes that the arr1 array is not used since it thinks it can remove the decrement. Am I violating some convention in the above code? What could cause this behavior? It is a very old piece of f2c-translated code, the pointer decrement is due to the 1-based indexing of the original code.

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• Should downcasting be avoided while using a class hierarchy in C++?

  - by neuviemeporte

  Let's say I'm writing an application which works with projects, and exposes different functionality depending on the type of the project. I have a hierarchy of classes for the different types of projects: class AbstractProject { }; class ProjectA : public AbstractProject { }; class ProjectB : public AbstractProject { }; class ProjectC : public AbstractProject { }; Now, I was planning to have an AbstractProject *_currentProject pointer as a member in the application's main class, pop up a dialog box on startup and based on the selection, do: _currentProject = new ProjectB(); // e.g. Later, I'll have to downcast the pointer to the specific type to utilize the functionality specific to different Project-s. Somehow this makes me feel uneasy. Is there a Better Way of doing this?

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• Does C++ require a destructor call for each placement new?

  - by Josh Haberman

  I understand that placement new calls are usually matched with explicit calls to the destructor. My question is: if I have no need for a destructor (no code to put there, and no member variables that have destructors) can I safely skip the explicit destructor call? Here is my use case: I want to write C++ bindings for a C API. In the C API many objects are accessible only by pointer. Instead of creating a wrapper object that contains a single pointer (which is wasteful and semantically confusing). I want to use placement new to construct an object at the address of the C object. The C++ object will do nothing in its constructor or destructor, and its methods will do nothing but delegate to the C methods. The C++ object will contain no virtual methods. I have two parts to this question. Is there any reason why this idea will not work in practice on any production compiler? Does this technically violate the C++ language spec?

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• Can I control the mouse cursor from within R?

  - by Bernd Meyer

  Is it possible, to control the mouse pointer from the R console? I have something like this in mind: move_mouse(x_pos=100,y_pos=200) # move the mouse pointer to position (100,200) mouse_left_button_down # simulate a press of the left button move_mouse(x_pos=120,y_pos=250) # move mouse to select something mose_release_left_button # release the pressed button In MATLAB, something like this is possible with the following code import java.awt.Robot; mouse = Robot; mouse.mouseMove(0, 0); mouse.mouseMove(100, 200); Is something similar possible for the keybord? E.g. simulate keybord events?

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• Regarding C typedef struct

  - by Bruce Duncan

  I have multiple instances of typedef struct box so box box1, box box2 etc. The members of the struct are length, width, height etc. typedef struct { int width; int height; } box; box box1; box box2; How can I create a function that operates on all the width members of each box instance? My confusion is how do I pass a pointer to a typedef struct member that works across all instances of box. I know how to pass a pointer to a specific instance member like box1.width but how to pass .width and then do box1.width=value; box2.width=value; box3.width=value; within the function?

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• C++ DWORD* to BYTE*

  - by NomeSkavinski

  My issue, i am trying to convert and array of dynamic memory of type DWORD to a BYTE. Fair enough i can for loop through this and convert the DWORD into a BYTE per entry. But is their a faster way to do this? to take a pointer to DWORD data and convert the whole piece of data into a pointer to BYTE data? such as using a memcpy operation? I feel this is not possible, im not requesting an answer just an experienced opinion on my approach, as i have tried testing both approaches but seem to fail getting to a solution on my second solution. Thanks for any input, again no answers just a point in the right direction. Nor is this a homework question, i felt that had to be mentioned.

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• Why does OpenGL's glDrawArrays() fail with GL_INVALID_OPERATION under Core Profile 3.2, but not 3.3 or 4.2?

  - by metaleap

  I have OpenGL rendering code calling glDrawArrays that works flawlessly when the OpenGL context is (automatically / implicitly obtained) 4.2 but fails consistently (GL_INVALID_OPERATION) with an explicitly requested OpenGL core context 3.2. (Shaders are always set to #version 150 in both cases but that's beside the point here I suspect.) According to specs, there are only two instances when glDrawArrays() fails with GL_INVALID_OPERATION: "if a non-zero buffer object name is bound to an enabled array and the buffer object's data store is currently mapped" -- I'm not doing any buffer mapping at this point "if a geometry shader is active and mode? is incompatible with [...]" -- nope, no geometry shaders as of now. Furthermore: I have verified & double-checked that it's only the glDrawArrays() calls failing. Also double-checked that all arguments passed to glDrawArrays() are identical under both GL versions, buffer bindings too. This happens across 3 different nvidia GPUs and 2 different OSes (Win7 and OSX, both 64-bit -- of course, in OSX we have only the 3.2 context, no 4.2 anyway). It does not happen with an integrated "Intel HD" GPU but for that one, I only get an automatic implicit 3.3 context (trying to explicitly force a 3.2 core profile with this GPU via GLFW here fails the window creation but that's an entirely different issue...) For what it's worth, here's the relevant routine excerpted from the render loop, in Golang: func (me *TMesh) render () { curMesh = me curTechnique.OnRenderMesh() gl.BindBuffer(gl.ARRAY_BUFFER, me.glVertBuf) if me.glElemBuf > 0 { gl.BindBuffer(gl.ELEMENT_ARRAY_BUFFER, me.glElemBuf) gl.VertexAttribPointer(curProg.AttrLocs["aPos"], 3, gl.FLOAT, gl.FALSE, 0, gl.Pointer(nil)) gl.DrawElements(me.glMode, me.glNumIndices, gl.UNSIGNED_INT, gl.Pointer(nil)) gl.BindBuffer(gl.ELEMENT_ARRAY_BUFFER, 0) } else { gl.VertexAttribPointer(curProg.AttrLocs["aPos"], 3, gl.FLOAT, gl.FALSE, 0, gl.Pointer(nil)) /* BOOM! */ gl.DrawArrays(me.glMode, 0, me.glNumVerts) } gl.BindBuffer(gl.ARRAY_BUFFER, 0) } So of course this is part of a bigger render-loop, though the whole "*TMesh" construction for now is just two instances, one a simple cube and the other a simple pyramid. What matters is that the entire drawing loop works flawlessly with no errors reported when GL is queried for errors under both 3.3 and 4.2, yet on 3 nvidia GPUs with an explicit 3.2 core profile fails with an error code that according to spec is only invoked in two specific situations, none of which as far as I can tell apply here. What could be wrong here? Have you ever run into this? Any ideas what I have been missing?

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• Passing arguments to UILabel [ 2 ] *

  - by DesperateLearner

  I'm trying to call a method of the below (Scroll animation class) type from a viewcontroller class. -(void)CreateLabel:(CGRect )frame andLabel:(UILabel *[NUM_LABELS])label andview:(UIView *)view; I got some errors when I tried passing the argument. Any suggestion on how to call this? This is how I called that method ScrollAnimation *newAnimation = [[ScrollAnimation alloc] init]; [newAnimation CreateLabel:CGRectMake(0, 50, 300,30) andLabel:animateLabel[NUM_LABELS] andview:self.view]; I have the error /Volumes/Red Drive/CarTransition/CarTransition/ViewController.m:120:66: Implicit conversion of an Objective-C pointer to 'UILabel **' is disallowed with ARC /Volumes/Red Drive/CarTransition/CarTransition/ViewController.m:120:66: Incompatible pointer types sending 'UILabel *__strong' to parameter of type 'UILabel **'

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• allocator with no template

  - by Merni

  Every stl container take an allocator as a second object, template < class T, class Allocator = allocator<T> > class vector; If you write your own class It is possible to use your own allocator. But is it possible to write your own allocator without using templates? For example, writing this function is not easy if you are not allowed to use templates pointer allocate(size_type n, const_pointer = 0) { void* p = std::malloc(n * sizeof(T)); if (!p) throw std::bad_alloc(); return static_cast<pointer>(p); } Because how could you know the size of T?

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• Implementing zoom on a fixed point, javascript/canvas

  - by csiz

  I want to implement zooming on the mouse pointer with the mouse wheel. That is scaling the image while the point under the mouse pointer stays fixed. Here is my code, which doesn't work very well var scala = 1 + event.wheelDelta / 1000; canvas.context.translate(-canvas.mouse.x * ( scala - 1 ) / canvas.scale,-canvas.mouse.y * ( scala - 1 ) / canvas.scale); canvas.context.scale(scala,scala); canvas.scale *= scala; //canvas.scale is my variable that is initially set to 1. //canvas.mouse is my variable that represents the mouse position relative to the canvas

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• Percentage position move

  - by HasanGursoy

  Is there a simple way to move percentage pointer after the value: 120 @ %60 {a} >> 120 @ 60% {a}

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• what is the Different categories of pointers?

  - by subodh

  Can any body explains about the different categories of pointer(like wild pointers)?

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• What object called a method in Obj-C

  - by Loz

  Hi, I am looking to write a plugin controller in Cocoa that loads bundles, and exposes a specific set of methods for the plugins to call. My question is this: is it possible to know (any) info about the object that called a method in the controller. When an instantiated plugin calls a method in my plugin controller, I would like to know which of the plugin instances called the method, without having to rely on the plugin sending a pointer to itself as a parameter (I could always validate the pointer they send, but I want to keep the API methods as simple as possible). There may be no perfect solution (and there are simple workarounds), but it's always good to learn some new tricks if possible (or the reasons why it's impossible). Thanks in advance.

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• What is wrong with my version of strchr?

  - by Eduard Saakashvili

  My assignment is to write my own version of strchr, yet it doesn't seem to work. Any advice would be much appreciated. Here it is: char *strchr (const char *s, int c) //we are looking for c on the string s { int dog; //This is the index on the string, initialized as 0 dog = 0; int point; //this is the pointer to the location given by the index point = &s[dog]; while ((s[dog] != c) && (s[dog] != '\0')) { //it keeps adding to dog until it stumbles upon either c or '\0' dog++; } if (s[dog]==c) { return point; //at this point, if this value is equal to c it returns the pointer to that location } else { return NULL; //if not, this means that c is not on the string } }

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• How to pass a member function to a function used in another member function?

  - by Tommaso Ferrari

  I found something about my problem, but I don't already understand very well. I need to do something like this: class T{ double a; public: double b; void setT(double par){ a=par; }; double funct(double par1) { return par1/a; } void exec(){ b=extfunct(funct, 10); } } double extfunct(double (*f)(double),double par2){ return f(par2)+5; } Operation and function are only for example, but the structure is that. The reason of this structure is that I have a precostituited class which finds the minimum of a gived function (it's extfunct in the example). So I have to use it on a function member of a class. I understood the difference between pointer to function and pointer to member function, but I don't understand how to write it. Thanks, and sorry for the poor explanation of the problem.

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• C++ String pointers

  - by gnm

  In my previous app I had an object like this: class myType { public: int a; string b; } It had a lot of instances scattered everywhere and passed around to nearly every function. The app was slow. Profiling said that 95% of time is eaten by the string allocator function. I know how to work with the object above, but not how to work with string pointers. class myType { public: int a; string* b; } They told me to use pointers as above. How much faster is it with a string pointer? What is copied when I copy the object? How to the following using the class with the pointer: Access the string value Modify the string value without modifying the one in the object (copy?) General things that change if I use string pointers?

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• Proper way to handle issue when porting 32 to 64 bit. Conversion from DT1 to DT2 of greater size

  - by grobartn

  So I am trying to port 32 bit to 64 bit. I have turned on the VS2008 flag for detecting problems with 64 bit. I am trying following: char * pList = (char *)uiTmp); warning C4312: 'type cast' : conversion from 'unsigned int' to 'char *' of greater size Disregard the code itself. This is also true for any pointer, because 64 bit pointer is greater than 32 bit unsigned int or int for that purpose. Given that you have to cast smaller type to greater how would you go about doing it so it correctly on both 32/64 bit systems

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• read successive frames OpenCV using cvQueryframe

  - by AtharvaI

  Hi all I have a basic question in regards to cvQueryFrame() in OpenCV. I have the following code: IplImage *frame1,*frame2; frame1 = cvQueryFrame(capture); frame2 = cvQueryFrame(capture); Now my question is: if frame1 is a pointer to the first frame, is frame2 a pointer to the 2nd frame? So will the two cvQueryFrame() calls read successive frames? I thought I'd check myself first but the pointers frame1,frame2 seem to have the same hex value. :s I just need to capture two frames at a time and then need to process them. Thanks in advance

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• Need recommendation for object serialization library in c++

  - by michael

  Hi, I am looking for recommendation for object serialization/deserialization library in c++? Which one are the most advanced and open-sourced? Can it handle Any class that users defined? Object hierarchy (parent and child classes)? A Tree of objects? Class A has an attribute of Class B which has an attribute of Class C? STL containers? Class A has a vector of Class B? A cyclic of objects? Class A has a pointer pointing to B which has a pointer to A? I find boost serialization library. I am not sure what is its limitation from http://www.boost.org/doc/libs/1_42_0/libs/serialization/doc/tutorial.html

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• Record Name field in DNS responce

  - by Lescott

  I just read about DNS protocol, and found, that the name field can be writen in two ways: lenght of the next label the label lenght of the next label the label ... zero-byte pointer to the previous name field Next is the original article fragment: The Resource Record Name field is encoded in the same way as the Question Name field unless the name is already present elsewhere in the DNS message, in which case a 2-byte field is used in place of a length-value encoded name and acts as a pointer to the name that is already present. So, my question is, how can I determine the first or the second way is using in a package?

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• What is the result of "new int[ 0 ]"? [closed]

  - by ArunSaha

  Possible Duplicates: What does zero-sized array allocation do/mean? C++ new int[0] — will it allocate memory? int * p; p = new int[ 0 ]; What is the expected outcome when new is called for zero number of elements? Is the outcome defined or undefined? Further, is it okay to call delete [] p; on that pointer? What is the intuition/analogy to this situation of pointer to an array of zero elements? Thanks in advance. Regards, Arun

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