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  • Allocating memory for a char pointer that is part of a struct

    - by mrblippy
    hi, im trying to read in a word from a user, then dynamically allocate memory for the word and store it in a struct array that contains a char *. i keep getting a implicit declaration of function âstrlenâ so i know im going wrong somewhere. struct class { char class_code[4]; char *name; }; char buffer[101]; struct unit units[1000]; scanf("%s", buffer); units[0].name = (char *) malloc(strlen(buffer)+1); strcpy(units[0].name, buffer);

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  • Pointer and malloc issue

    - by Andy
    I am fairly new to C and am getting stuck with arrays and pointers when they refer to strings. I can ask for input of 2 numbers (ints) and then return the one I want (first number or second number) without any issues. But when I request names and try to return them, the program crashes after I enter the first name and not sure why. In theory I am looking to reserve memory for the first name, and then expand it to include a second name. Can anyone explain why this breaks? Thanks! #include <stdio.h> #include <stdlib.h> void main () { int NumItems = 0; NumItems += 1; char* NameList = malloc(sizeof(char[10])*NumItems); printf("Please enter name #1: \n"); scanf("%9s", NameList[0]); fpurge(stdin); NumItems += 1; NameList = realloc(NameList,sizeof(char[10])*NumItems); printf("Please enter name #2: \n"); scanf("%9s", NameList[1]); fpurge(stdin); printf("The first name is: %s",NameList[0]); printf("The second name is: %s",NameList[1]); return 0; }

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  • C++ Add this pointer to a container by calling it in base class constructor

    - by vivekeviv
    class Base { public: Base (int a, int b); private: int a,b; }; class Derived1 { public: Derived1():base(1,2){} }; similarly Derived2, Derived 3 which doesnt contain any data members on its own Now i need to contain these derived objects in a singleton, so i was thinking to call this in base constructor like Base::Base(int a, int b) { CBaseMgr::GetInstance()->AddtoVector(this); } so now if i construct Derived d1, d2, d3 etc. will the Singleton's container contain all derived objects? My doubt is can i do this adding of objects to container in base ctor or should i do in derived ctor.?

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  • How to use pointers and pointer aritmetic

    - by booby
    : error C2064: term does not evaluate to a function taking 1 arguments : error C2227: left of '-name' must point to class/struct/union/generic type how do i fix this so this error doesn't happen for(int index = 0; index < (numStudents); index++) { if (student(index + 1)->score >= 90 ) student(index + 1)->grade = 'A'; else if (student(index + 1)->score >= 80 ) student(index + 1)->grade = 'B'; else if (student(index + 1)->score >= 70 ) student(index + 1)->grade = 'C'; else if (student(index + 1)->score >= 60 ) student(index + 1)->grade = 'D'; else student(index + 1)->grade = 'F'; }

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  • Read from file into pointer to struct

    - by cla barzu
    I need help with pointers in C. I have to read from a file, and fill an array with pointers to struct rcftp_msg . Since now I did the next things: struct rcftp_msg { uint8_t version; uint8_t flags; uint16_t len; uint8_t buffer[512]; }; struct rcftp_msg *windows [10]; pfile = fopen(file,"r"); // Open the file I have to read from the file into the buffer, but I don't know how to do it. I tried the next: for (i = 0; i <10; i++){ leng=fread (**windows[i]->buffer**,sizeof(uint8_t),512,pfile); } I think windows[i]-buffer is bad, cuz that don't work. Sorry for my bad English :(

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  • Freeing memory with Pointer Arithmetic

    - by Breedly
    C++ newb here. I'm trying to write my own implementation of an array using only pointers, and I've hit a wall I don't know how to get over. My constructor throws this error array.cpp:40:35: error: invalid conversion from ‘int*’ to ‘int’ [-fpermissive] When my array initializes I want it to free up all the spaces in the array for ints. Array::Array(int theSize){ size = theSize; int *arrayPointer = new int; int index = 0; while(theSize > index){ *(arrayPointer + index) = new int; //This is the trouble line. ++index; } } What am I doing wrong stackoverflow?

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  • Null pointer exception on .iterator() call

    - by Peter
    I'm getting a strange NullPointerException, evidently thrown by the following line of code: Iterator<Note> it = notes.iterator(); I've checked, and at the time the java.util.TreeSet notes is always non-null (with 15 elements). The TreeSet API says nothing about iterator() throwing NullPointerExceptions. What else could be going here?

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  • Passing a pointer to an array to glGenBuffers

    - by Josh Elsasser
    I'm currently passing an array to a function, then attempting to use glGenBuffers with the array that is passed to the function. I can't figure out a way to get glGenBuffers to work with the array that I've passed. I have a decent grasp of the basics of pointers, but this is beyond me. This is basically how the render code works. It's a bit more complex, (colours using the same array idea, also not working) but the basic idea is as follows: void drawFoo(const GLfloat *renderArray, GLuint verticeBuffer) { glBindBuffer(GL_ARRAY_BUFFER, verticeBuffer); glBufferData(GL_ARRAY_BUFFER, sizeof(verticeBuffer)*sizeof(GLfloat), verticeBuffer, GL_STATIC_DRAW); glVertexPointer(2, GL_FLOAT, 0, 0); glEnableClientState(GL_VERTEX_BUFFER); glDrawArrays(GL_TRIANGLE_FAN, 0, 45); glDisableClientState(GL_VERTEX_BUFFEr); } Thanks in advance for the help

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  • Duplicate array but maintain pointer links

    - by St. John Johnson
    Suppose I have an array of nodes (objects). I need to create a duplicate of this array that I can modify without affecting the source array. But changing the nodes will affect the source nodes. Basically maintaining pointers to the objects instead of duplicating their values. // node(x, y) $array[0] = new node(15, 10); $array[1] = new node(30, -10); $array[2] = new node(-2, 49); // Some sort of copy system $array2 = $array; // Just to show modification to the array doesn't affect the source array array_pop($array2); if (count($array) == count($array2)) echo "Fail"; // Changing the node value should affect the source array $array2[0]->x = 30; if ($array2[0]->x == $array[0]->x) echo "Goal"; What would be the best way to do this?

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  • Indexing with pointer C/C++

    - by Leavenotrace
    Hey I'm trying to write a program to carry out newtons method and find the roots of the equation exp(-x)-(x^2)+3. It works in so far as finding the root, but I also want it to print out the root after each iteration but I can't get it to work, Could anyone point out my mistake I think its something to do with my indexing? Thanks a million :) #include <stdio.h> #include <math.h> #include <malloc.h> //Define Functions: double evalf(double x) { double answer=exp(-x)-(x*x)+3; return(answer); } double evalfprime(double x) { double answer=-exp(-x)-2*x; return(answer); } double *newton(double initialrt,double accuracy,double *data) { double root[102]; data=root; int maxit = 0; root[0] = initialrt; for (int i=1;i<102;i++) { *(data+i)=*(data+i-1)-evalf(*(data+i-1))/evalfprime(*(data+i-1)); if(fabs(*(data+i)-*(data+i-1))<accuracy) { maxit=i; break; } maxit=i; } if((maxit+1==102)&&(fabs(*(data+maxit)-*(data+maxit-1))>accuracy)) { printf("\nMax iteration reached, method terminated"); } else { printf("\nMethod successful"); printf("\nNumber of iterations: %d\nRoot Estimate: %lf\n",maxit+1,*(data+maxit)); } return(data); } int main() { double root,accuracy; double *data=(double*)malloc(sizeof(double)*102); printf("NEWTONS METHOD PROGRAMME:\nEquation: f(x)=exp(-x)-x^2+3=0\nMax No iterations=100\n\nEnter initial root estimate\n>> "); scanf("%lf",&root); _flushall(); printf("\nEnter accuracy required:\n>>"); scanf("%lf",&accuracy); *data= *newton(root,accuracy,data); printf("Iteration Root Error\n "); printf("%d %lf \n", 0,*(data)); for(int i=1;i<102;i++) { printf("%d %5.5lf %5.5lf\n", i,*(data+i),*(data+i)-*(data+i-1)); if(*(data+i*sizeof(double))-*(data+i*sizeof(double)-1)==0) { break; } } getchar(); getchar(); free(data); return(0); }

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  • When convert a void pointer to a specific type pointer, which casting symbol is better, static_cast or reinterpret_cast?

    - by BugCreater
    A beginner question with poor English: Here I got a void* param and want to cast(or change) it to a specific type. But I don't know which "casting symbol" to use. Either**static_cast** and reinterpret_cast works. I want to know which one is better? which one does the Standard C++ recommend? typedef struct { int a; }A, *PA; int foo(void* a) // the real type of a is A* { A* pA = static_cast<A*>(a); // or A* pA = reinterpret_cast<A*>(a);? cout<<pA->a<<endl; return 0; } Here I use A* pA = static_cast(a); or A* pA = reinterpret_cast(a); is more proper?

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  • Pointer mysteriously moves

    - by Armen Ablak
    Hi, I have this code for Node rotation and in a line which is marked something happens and I don't really know what and why :). //Test case 30 \ 16 / 29 RotationRight(node->mParent); //call template<class T> void SplayTree<T>::RotationRight(SplayNode<T> *&node) const { SplayNode<T> *left = node->mLeft; SplayNode<T> *parent = node->mParent; node->mLeft = left->mRight; if(left->HasRight()) left->mRight->mParent = node; left->mRight = node; //node in this line points to 0x00445198 {30} left->mParent = node->mParent; //and in this line it points to 0x00444fb8 {16} (node, not node->mParent) node->mParent = left; node = left; } Well, left-mParent points to node also, so I basically do node = node-mParent. The problem is I can't find a work around - how to unpin in from node and change it's pointing address without changing it's.

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  • Disallow taking pointer/reference to const to a temporary object in C++ (no C++0X)

    - by KRao
    Hi, I am faced with the following issue. Consider the following class: //Will be similar to bost::reference_wrapper template<class T> class Ref { public: explicit Ref(T& t) : m_ptr(&t) {} private: T* m_ptr; }; and this function returning a double double fun() {return 1.0;} If we now have double x = 1.0; const double xc = 1.0; Ref<double> ref1(x); //OK Ref<const double> refc1(cx); //OK good so far, however: //Ref<double> ref2( fun() ); //Fails as I want it to Ref<const double> refc2( fun() ); //Works but I would like it not to Is there a way to modify Ref (the way you prefer) but not the function fun, so that the last line returns a compile-time error? Please notice you can modify the constructor signature (as long as I am able to initialise the Ref as intended). Thank you in advance for your help!

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  • Doubt on pointer conversion

    - by Simone
    Suppose we have the following code: #include <iostream> struct A { virtual void f() { std::cout << "A::f()" << std::endl; } }; struct B: A { void f() { std::cout << "B::f()" << std::endl; } }; void to_A(void* voidp) { A* aptr = static_cast<A*>(voidp); aptr->f(); } void to_B(void* voidp) { B* bptr2 = static_cast<B*>(voidp); bptr2->f(); } int main() { B* bptr = new B; void* voidp = bptr; to_A(voidp); // prints B::f() to_B(voidp); // prints B::f() } is this code guaranteed to always work as in the code comments or is it UB? AFAIK it should be ok, but I'd like to be reassured.

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  • Dereferencing possible null pointer in java

    - by Nealio
    I am just starting to get into graphics and when I am trying to get the graphics, I get the error"Exception in thread "Thread-2" java.lang.NullPointerException" and I have no clue on what is going on! Any help is greatly appreciated. //The display class for the game //Crated: 10-30-2013 //Last Modified: 10-30-2013 package gamedev; import gamedev.Graphics.Render; import gamedev.Graphics.Screen; import java.awt.Canvas; import java.awt.Dimension; import java.awt.Graphics; import java.awt.Toolkit; import java.awt.image.BufferStrategy; import java.awt.image.BufferedImage; import java.awt.image.DataBufferInt; import javax.swing.JFrame; private void tick() { } private void render() { System.out.println("display.render"); BufferStrategy bs = this.getBufferStrategy(); if (bs == null) { createBufferStrategy(3); } for (int i = 0; i < GAMEWIDTH * GAMEHEIGHT; i++) { pixels[i] = screen.PIXELS[i]; } screen.Render(); //The line of code that is the problem Graphics g = bs.getDrawGraphics(); //end problematic code g.drawImage(img, 0, 0, GAMEWIDTH, GAMEHEIGHT, null); g.dispose(); bs.show(); }

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  • Would a pointer to a pointer to nil match against NULL?

    - by dontWatchMyProfile
    Example: A validation method contains this check to see if an NSError object shall be created or not: - (BOOL)validateCompanyName:(NSString *)newName error:(NSError **)outError { if (outError != NULL) { // do it... Now I pass an NSError object, like this: NSError *error = nil; BOOL ok = [self validateCompanyName:@"Apple" error:&error]; I'm not sure if this matches the check for not NULL. I think it's not NULL, since I believe NULL is not nil. Maybe someone can clear this up?

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  • Delegates with explicit "this" pointer?

    - by Qwertie
    Is it possible to adapt a method like this function "F" class C { public void F(int i); } to a delegate like Action<C,int>? I have this vague recollection that Microsoft was working on supporting this kind of adaptation. But maybe I misremembered!

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  • how to make struct member pointer in assembly?

    - by sillis
    I`m trying to create a macro which would make easier to point to a structs member. Currently i am pointing to a structs member in assembly file using the STRUCT_NAME + offset method. For example if i want to point structs third member,i would have to do it like this: STRUCT_NAME + 3. This seems stupid way to do it, and if i insert more members in the struct, i have to update all the offset values in the code. Is there a way to point using STRUCT_NAME + macro(struct_name, member_name) ? I`m using texas instruments TMS320C28x hardware. Thanks!

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  • What does this pointer-heavy C code do?

    - by justRadojko
    Could someone explain to me what should two following lines do: s.httpheaderline[s.httpheaderlineptr] = *(char *)uip_appdata; ++((char *)uip_appdata); This is taken from uIP code for microcontrollers. s - structure httpheaderline - http packet presented as a string httpheadrlineptr - integer value uip_appdata - received ethernet packet (string) If some more info is needed please let me know. BTW. Eclipse is reporting an error on the second line with message Invalid lvalue in increment so i'm trying to figure out how to solve this.

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  • Void pointer cast C++ and GTK

    - by Tarantula
    See this GTK callback function: static gboolean callback(GtkWidget *widget, GdkEventButton *event, gpointer *data) { AnyClass *obj = (AnyClass*) data; // using obj works } (please note the gpointer* on the data). And then the signal is connected using: AnyClass *obj2 = new AnyClass(); gtk_signal_connect(/*GTK params (...)*/, callback, obj2); See that the *AnyClass is going to be cast to gpointer* (void**). In fact, this is working now. The callback prototype in GTK documentation is "gpointer data" and not "gpointer *data" as shown in code, what I want to know is: how this can work ? Is this safe ?

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  • Cast A primitive type pointer to A structure pointer - Alignment and Padding?

    - by Seçkin Savasçi
    Just 20 minutes age when I answered a question, I come up with an interesting scenario that I'm not sure of the behavior: Let me have an integer array of size n, pointed by intPtr; int* intPtr; and let me also have a struct like this: typedef struct { int val1; int val2; //and less or more integer declarations goes on like this(not any other type) }intStruct; My question is if I do a cast intStruct* structPtr = (intStruct*) intPtr; Am I sure to get every element correctly if I traverse the elements of the struct? Is there any possibility of miss-alignment(possible because of padding) in any architecture/compiler?

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  • javascript function pointer and "this"

    - by Justin808
    I'm passing a method as a variable to be used as a callback. When its called, the "this" is not the object the method is a member of. How do I go about getting access to the method's object instance so I can get access to it variables and other member functions? I have no control over the callback call method, its a separate library. All I do is call the binding from my object init method. I would have expected this inside my _connection method to have been its object. jsPlumb.bind('connection', this._connection);

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  • Misaligned Pointer Performance

    - by Elite Mx
    Aren't misaligned pointers (in the BEST possible case) supposed to slow down performance and in the worst case crash your program (assuming the compiler was nice enough to compile your invalid c program). Well, the following code doesn't seem to have any performance differences between the aligned and misaligned versions. Why is that? /* brutality.c */ #ifdef BRUTALITY xs = (unsigned long *) ((unsigned char *) xs + 1); #endif ... /* main.c */ #include <stdio.h> #include <stdlib.h> #define size_t_max ((size_t)-1) #define max_count(var) (size_t_max / (sizeof var)) int main(int argc, char *argv[]) { unsigned long sum, *xs, *itr, *xs_end; size_t element_count = max_count(*xs) >> 4; xs = malloc(element_count * (sizeof *xs)); if(!xs) exit(1); xs_end = xs + element_count - 1; sum = 0; for(itr = xs; itr < xs_end; itr++) *itr = 0; #include "brutality.c" itr = xs; while(itr < xs_end) sum += *itr++; printf("%lu\n", sum); /* we could free the malloc-ed memory here */ /* but we are almost done */ exit(0); } Compiled and tested on two separate machines using gcc -pedantic -Wall -O0 -std=c99 main.c for i in {0..9}; do time ./a.out; done

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