C++ :: Performance Penalty For Repeatedly Dereferencing A Pointer?
Oct 2, 2013
Let's assume "person" is a class that has a member "age", and personptr is a pointer to a person object.
doStuff(personptr->age);
doMoreStuff(personptr->age);
andSomethingElse(personptr->age);
andSomethingElse(personptr->age);
Is this bad for performance? Is the following better or doesn't it matter?
int person_age = personptr->age;
doStuff(person_age);
doMoreStuff(person_age);
andSomethingElse(person_age);
andSomethingElse(person_age);
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Apr 14, 2014
I could understand void pointers I created the following program:
Code:
#include <stdio.h>
#include <string.h>
int main(void) {
char word[] = "Zero";
int number = 0;
void *ptr = NULL;
[Code] .....
The program works fine, however i really want to fully understand what is going on with the dereferencing of the void pointer, for example: With the following code:
Code:
ptr = &number;
*((int *)ptr) = 1;
Why can't you just do:
Code:
ptr = &number;
*(int *)ptr = 1;
And again with this code, (i'm guessing it's becuase its a pointer to a pointer?):
Code:
ptr = &word;
strcpy(ptr,"One");
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Feb 27, 2014
keep getting "deferencing pointer to incomplete type" on the bold lines:
main:
int main(int argc, char *argv[]) {
printf("Please think of an animal. I will try to find out what it is by asking you some yes/no questions.");
struct treenode *root = mkTreeNode("Is it a reptile?
", NULL, NULL);
struct treenode *selectedNode = root;
root->left = mkTreeNode("Does it have legs?
[code]....
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Feb 21, 2015
I've been writing the math functions for a 3d game and tried compiling it at about 30 functions in. I get this error related to my pointers to my structures. it affects almost everything in all my functions (as youll see by looking at how i do the math in the function below). The compiler gives me the error
"error: dereferencing pointer to incomplete type"
on all my struct Type4D pointers but referencing the values in my struct TypeMatrix4X4 using pointers seems to work fine i think (it doesn't seem to complian explicitly about it. so here is the important code...
one example function
Code:
struct Type4D *MatVecMult4X4RtoL(struct TypeMatrix4X4 *mat, struct Type4D *vec) {
struct Type4D *dest = (struct Type4D *) malloc(sizeof(struct Type4D));
[Code]....
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Jul 10, 2013
I am having trouble with this program I get the error dereferencing pointer to incomplete type in the populate function I am using BloodShed's Dev C++ compiler v4.9.9.2 I copied this program out of a book because I was having a problem with a linked list in a similar program. I think there is a problem with the compiler not supporting these types of pointer's in a function.
#include <stdio.h>
struct tel_typ {
char name[25];
char phone_no[15];
struct tel_typ *nextaddr;
[code].....
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Sep 13, 2014
I am getting this error:
drivers/media/video/mxc/capture/gt2005.c:2256:62: error: dereferencing pointer to incomplete type
I am at a loss trying to figure this out. Here it is:
case Sensor_Flash:
{
struct i2c_client *client = to_i2c_client(to_soc_camera_control(icd));
struct sensor *sensor = to_sensor(client);
if (sensor->sensor_io_request && sensor->sensor_io_request->sensor_ioctrl) {
sensor->sensor_io_request->sensor_ioctrl(icd->pdev,Cam_Flash, on);
if(on){
Lines 6 and 7 are giving me the same error. What am I doing wrong?
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Aug 16, 2014
I have started to move over to using Unicode, wide character null-terminated strings in my Windows programmes. Accordingly I set the Use Unicode Character Set Visual C++ compiler option. It is my understanding that once you do that the many macros which determine whether you transparently call ...A() or ...W() API functions automatically shift over to calling the wide character variants. As this is a compiler directive, all the choices are made and hardcoded in to the resultant executable at compile/link-time BEFORE it is ever run. Therefore using for example the macro OpenFileName() in the source code instead of specifically calling OpenFileNameW() has no impact on run-time performance.
The next logical step, instead of explicitly using wchar_t is to declare null-terminated string character arrays as TCHAR*. Then, so long as I also employ the tcn... variants of CRT string functions and call TEXT() or _T() macros to create string literals the preprocessor will chose, again transparently whether to create an executable using standard multibyte or unicode wide characters - and their associated functions - all determined by the Use Unicode Character Set switch. That way I can cover both eventualities with the same source code.
So, with all that - I THINK!!! - properly under by belt, I am fairly sure that using TCHAR and its friends will not effect run-time performance at all. However, in his otherwise excellent article the author makes it sound as if using Unicode EXPLICITLY through wchar_t, ...W() API functions and tcn... CRT calls is faster than the TCHAR alternative.
At the end of the day my question is - have I got the right end of the stick; TCHAR makes no difference to executable performance?
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Nov 11, 2014
I have the following code:
class Element {
public:
..
virtual unsigned NumberOfNodes() = 0;
[Code] ....
Is it possible to implement this better? All the element stuff can be static, but this is not possible with the abstract class. I want to have Mesh independent of a specific element. With the code above, if I have multiple meshes I have one instance of an element, e.g., Triangle for each mesh. Although they are all exactly the same.
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Apr 6, 2015
I am trying to modify a PerformanceCounter I have created in C#. But it doesn't seem to be that it is being changed. This counter needs actualy to be a flag : 0 or 1.
I took the following code from the web. It created the collectors category along with the counters well. But the RawValue always shows 0!
I am working on Win7/64.
using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
namespace PerformanceCounterSample
[Code] ....
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Sep 26, 2014
I started to write a program that repeatedly reads in values for a,b and c and find the root of the polynomial
ax^2 + bx + c = 0
The program should print out for example:
two complex roots: root1 = -1.00000 + i*1.41421
root2 = -1.00000 - i*1.41421
My code:
#include <stdio.h>
#include <math.h>
int main(void){
int a,b,c;
printf("Choose the values of a, b and c for the equation ax^2 + bx + c");
scanf("%d%d%d
",a,b,c);
[code].....
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May 28, 2013
I have a certain piece of code that I want to run every 2 minutes. One of my ideas is to get the time and modules that with whatever number represents 2 minutes. Would this work?
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Apr 30, 2014
I know for while loops you type
while(argument){
do whatever
}
you have to use the brackets to enclose just like I used in my code right here.It is a simple while loop that is a countdown.
#include <iostream>
using namespace std;
int main() {
int n =10;
while(n>0){
cout << n << ", ";
[code].....
when I take the brackets away from my while loop, my code will still execute but it just prints out the number "10" repeatedly. I was just wondering why it does this and why the compiler does not throw out an error when I leave off the brackets after the "while()".
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Nov 29, 2013
I am asking for input for a char by using the _getch() function. The thing is that when a key is pressed multiple times it screws the program because it executes every single key that is entered.
I am asking for the user to enter a letter that will determine an action to be used in battle, like attack, magic, "use item", etc.
char option;
cout<<"Enter your choice for battle: ";
option=getch();
if(option=='a')
//Executes an attack
else if(option=='b')
//Opens magic menu
else if(option=='c')
//Opens item menu
Suppose the user enters a character, then the program executes an action by the enemy monster. This is where the problem arises, if the user entered multiple keys or if he enters input during the time the monster attacks, the next time it is the user's turn it will execute the first attack automatically because it keeps reading the input.
I want to know how to cut it off, so that it doesn't ruin the program like that.
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Aug 16, 2012
Here's what I'm trying to do : A simple readout that shows the input/feedback values for 10 different sensors (i.e. a motor, a thermocouple, light sensor, etc).
What I got so far:
The data is stored in 2 different arrays:
One array is a 2D string array that stores descriptions, and won't be changed:
Sensor ID, Sensor Type, Input Signal, Feedback Signal
["A"]["Motor"]["PWM Signal"]["RPM"]
["B"]["Thermocouple"]["N/A"]["TempC"]
etc
The second array is another 2D int array that stores all the data values:
Input Signal, Feedback Signal
[0][0] // for Sensor A, Input is 0 PWM, 0 RPM read from sensor
[0][25] // for Sensor B, Input is 0, 25C read from sensor
etc
My question: I'd like to re-write the code to incorporate the new things I learned in c++. Right now, the descriptions for all 10 sensors are in 1 array and the sensor values are in another array. If I use pointers to access the values, is there a performance difference between:
1. Keeping it as is, with 2 2d arrays
2. 1 big structure that has descriptions and sensor values for all 10 sensors (i.e. combining everything into 1)
3. 1 parent class, and 10 different objects for each sensor (i.e. splitting into 10)
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May 1, 2013
Write a user-friendly C++ program that allows a user to select repeatedly an operation to be performed from a displayed menu of actions. The menu includes the following items:
1. Simple Statistics
2. Vector Addition
3. Dot Product
4. Exit
The menu actions are described by the following points:
Simple Statistics: This action includes finding the average, and standard deviation of a list of data items. The option should allow the user to specify the name of a file from which the data are read into an array. All the results of this option are displayed on the screen.
Vector Addition: This action allows the user to enter the name of a file from which two vectors, V1 and V2, of equal size N are read. Accordingly, the two vectors are added, and displayed along with the resultant vector on the screen. Your program should check that the two added vectors are of the same size. Otherwise, the program should display a message and allow the user to make another choice from the menu.
Dot Product: This action is similar to the Vector Addition in terms of input, output, and checking validity of the vector operands.
Exit: This action terminates the program.
Your program should include at least the following functions:
1. A function, called ReadVector(), which reads a vector of any size from a given file name, and returns the vector and its size to the caller. The function prototype is defined as follows:
void ReadVector(double V[], int &size, ifstream infile);
2. A function, called DisplayMenu(), which displays the menu and returns the user’s choice as an integer value between 1 and 4. The function prototype is defined as follows:
int DisplayMenu (void);
3. A function, called VectorAdd(), which performs the addition of two vectors, A and B, and returns the resultant vector, C. The function prototype is defined as follows:
void VectorAdd(const double A[], const double B[], double C[], int size);
The sum of two vectors, A = (a1, a2, …, an) and B = (b1, b2, …, bn) of size n, is defined as: C = A + B.
Where, C = (c1, c2, …, cn), and ci = ai + bi, for1 i n .
4. A function, called DotProduct(), which performs the dot product of two vectors, A and B, and returns the result. The function prototype is defined as follows:
void DotProduct(const double A[], const double B[], int size, double &result);
The dot-product of two vectors A = (a1, a2, …, an) and B = (b1, b2, …, bn) of size n is defined as
n n
n
i
i i b a ....... b a b a b a B . A
1 1 2 2
1
5. A function, called Simple_Stat(), which finds the maximum, minimum, average, and standard deviation of a list of data items passed to it by a one-dimensional array. The function returns the average and standard deviation values. The function prototype is defined as follows:
void Simple_Stat(const double list[], int size, double &average, double
&std_dev);
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May 13, 2014
I have an school assignment that asks me to measure the most famous sorting algorithms for performance in terms of number of steps and CPU running time. ( Here I'm testing for running time)
I decided to test for bubble sort first:
#include <iostream>
#include <ctime>
using namespace std;
void bubbleSort(int ar[], int size) {
int temp;
[Code] ....
So basically what I want to know is:
1. Is this clock function giving the correct CPU running time?
2. Is there any way to write code that would measure the number of steps for each algorithm?
3.I need to test it for number of integers=100 then 200, then 300... Well you get my point, and I don't want to have to actually input 200 numbers with my keyboard. Is there any way to generate as many entries as I want?
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Nov 5, 2012
why doesnt the following program work as expected:
Code:
char x = 0xff;
char* y = &x;
if(*y == 0xff)
{
return 1;
}
return 0;
imo, it should return "1", but it doesnt. It seems like instead of comparing 0xff == 0xff, the compiler compares 0xffffffff == 0xff. Why?
If i use "byte" for this example, everything works as expected, even though it`s just defined as an "unsigned char".
Code:
typedef unsigned charbyte;
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Jan 11, 2014
I want to know how to dereference a void pointer through the way of typing it.
Lets just say that I malloc'd a huge bunch of memory and i can do whatever i want
void* randomData = malloc ( 1000000 );
And i decide to make my own virtual 'int'
I am not sure how to do this.
*( int* ) ( randomData + 10 ) = ( int ) 323453 //323453 can be an int variable aswell
Im not sure if this is the right way to do perform a dereference.
This is an overview of what has to be done:
-The pointer has to be dereferenced
-Cast the pointer as an int pointer so we can change it like a normal 4-byte int
-Perform pointer arithmetic, so that the int can be placed anywhere we want
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Jan 15, 2013
I have a set of functions at work which are incredibly useful, however it only supports labels that come from a specific database because that database contains information on the type. I'd like to re-create it to make it more applicable to any member/static/global variables but don't know how to store the type.
I've already re-written it to an extent, but it only accepts int types. I'd like to template it to accept any type. The trick is storing that type so that the pointer can be dereferenced at a later time which I don't know how to do.
Interface:
typedef int T; // The goal is to remove this line!
namespace TimerDelay {
void SetAfterDelay ( T* lpLabelAddress, float delay, T target = T(1)); // Queues the set
void ManageDelays ( float dt ); // sets the labels when appropriate
}
Source:
#include <vector>
namespace TimerDelay{
struct DelayObject {
void* address; // I will probably need to add a container
void* target; // to hold the type, but how can this be done?
[code]....
Edit:Is it possible to store a std::iterator_traits<> struct as a member of my structure? The g_list isn't templated as it needs to accept all types at the same time. That means that DelayObject cannot be templated. I think that means that I cannot use a templated member class as the size may be inconsistant.
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May 7, 2015
This is the main header with three classes, in summary ADNodeInstance is a data holder, ADNode is encapsulating a pointer to ADNodeInstance, and ADGraphBuilder is a main class which holds all the ADNodeInstances and manages them.:
Code:
#ifndef ADVIBE_STACK_H
#define ADVIBE_STACK_H
#include "memory"
#include "iostream"
#include "fstream"
#include "Eigen/Dense"
typedef Eigen::MatrixXd Matrix;
[Code] ....
From this all I could infer is that in the funcreateGradientMessage on the switch for TANH the segfault occurs for the expression: directGradient * child * (1 - child). From the output I can see that this is what happens in order:
Unary negation on node 5 resulting in 15Addition of node 16 and 15 (e.g. the brackets) resulting in 17trying to multiply 14 and 5 - SEGFAULT something wrong with 5
So my question is what exactly is happening? I tried to understand but can't.
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Jan 17, 2014
I was having problems changing the value of my head node I passed it as an argument as head which would be the address. The parameter was defined as struct node *head. like this
bool deleteNode(struct node *head, struct node *delptr)
I tried manipultaing pointer values to change head node value but it did not work. I saw some code online which used pointer to pointers(in code below) to change head node value it worked I dont fully understand why. Would like better understanding of why.
Would also like to know why the argument call needed &head instead of just head.
remove = deleteNode(&head,found); opposed to remove = deleteNode(head,found);
#include "stdafx.h"
#include<iostream>
struct node{
[Code].....
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Aug 19, 2014
I am attempting to implement function pointers and I am having a bit of a problem.
See the code example below; what I want to be able to do is call a function pointer from another pointer.
I'll admit that I may not be explaining this 100% correct but I am trying to implement the code inside the main function below.
class MainObject;
class SecondaryObject;
class SecondaryObject {
public:
[Code]....
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Nov 27, 2013
I have to write a program to print pascals triangle and stores it in a pointer to a pointer , which I am not entirely sure how to do. I also have to write the file and read it, then create a binary file. Assignment is attached. I am not the best with programming and especially with pointers. I will post my code below.
Code:
#include <stdio.h>
#include <stdlib.h>
void writePascalTriangle(char *fileName, int heightOfTriangle, int **triangle) {
FILE *fp;
fp=fopen("writePascalTriangle.txt", "w");
[Code] ....
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Apr 19, 2014
I'm making a system like twitter for class called ShoutOut.com I want to be able to get the PublicShoutOut pointer pointed to by the start iterator and assign it to firstShoutOutToDisplay and secondShoutOutToDisplay because I need that in order to pass the pointers to one of my functions. When I step through the debugger the values in start are all default values like "" and so are the values in this->firstShoutOutToDisplay but the message that start points to is being output just fine.
EDIT: got rid of irrelevant code. Am I using the correct syntax to do this?
if (start != finish) {
//getting these because a shoutout needs to be passed to the function that displays
//options for a shoutout
this->firstShoutoutToDisplay = (*start);
[Code] ....
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Mar 7, 2013
I have a function:
const void insertStuff(const void *key, const int value){
// I want to convert the void pointer into one
// of three types of pointers(int, string, or double)
switch(value){
case 0:
int *intPtr = key;
[Code] .....
But this causes an error of: "crosses initialization of int*intPtr"
What's the correct way of implementing this?
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Dec 25, 2013
i have been fiddling with pointers but I don't understand how the proper syntax is written when I want to acces an element of an array through a pointer to a pointer...The code is all mostly just random bs for learning purposes. I marked the problem "// THIS LINE"
Code:
#include <stdio.h>
#include <stdarg.h>
#include <stdlib.h>
#include <string.h>
#define MAX_DATA 100
int find_average(char *iden, ...) {
[Code]...
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