C :: Double Use Of Arrow Operator With Pointer / Function
Feb 24, 2015
I have recently come across a function call that I do not understand. It uses the arrow operator for a function call, twice, and I don't understand.
Code:
static inline void b43_write32(struct b43_wldev *dev, u16 offset, u32 value)
{
dev->dev->write32(dev->dev, offset, value);
}
I see that the function itself does not return anything but calls another function. The main difficulty I have is with the "dev->dev->" operator, where dev, I expect is a pointer to a structure.
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Jun 26, 2014
I understand that the dot operator is:
Code: a.b "a"
is the actual object (not a memory location) and "b" is the member. I also understand the arrow to mean:
Code: a->b "a"
is a pointer to a struct and "b" is it's member so "a" is dereferenced then "b" is given.
Here is where I get a little confused. I have a class:
exampleclass.h
Code:
#ifndef EXAMPLECLASS_H_INCLUDED
#define EXAMPLECLASS_H_INCLUDED
class exampleclass{
[Code].....
Also if ec1 had a public variable and I wanted to access it would it be referenced the same way as the method I call in ec1?
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Dec 22, 2014
I have int pointer called p and i want to calculate average.Since average involves using double or float so i am trying to convert this in the function averagetemp. It still gives me an error saying "cannot be converted"...
#include <iostream>
using namespace std;
int* createArray(int n);
int lowesttemp(int *p,int f);
int highesttemp(int *p,int f);
double averagetemp(int *k,double f);
void print(int *p,int lowest_temp,int highesttemp,int average_temp);
[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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Mar 13, 2013
how can we use modulus operator with double type variables
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May 17, 2014
while (getline(inStream, line))
{
while (inStream >> Student.getId() >> Student.FNAME >> Student.MINIT >> Student.LNAME >> Student.GENDER >> Student.UNITS >> Student.getGpa())
{
while (Student.getId() != id)
{
outStream << line << endl;
}
}
}
This is what I have right now. It shouldn't be a problem, but for some reason I am getting an error trying to >> Student.getGpa()
Error1error C2679: binary '>>' : no operator found which takes a right-hand operand of type 'double' (or there is no acceptable conversion)c:location1301Project 5
I will post more code if needed, but... I just don't know. I have a TON of code so I would rather not if I don't have to.
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Oct 24, 2013
I'm writing a program involving a theoretical hotel. Most of the code is already written, but the part I'm having trouble with involves the very beginning of the code.
The program is designed to read in from an input file the hotel's ID number, the types of rooms it has, the Room Numbers of each room, the base rate for each room, and the rate of additional charge per person.
The code demonstrates inheritance for my Object-Oriented Programming class, as each type of room will inherit from generic class Room, but I can't seem to figure out how to make the double-pointer for dynamic allocation work.
The code is below.
Hotel.h
Code:
class Hotel{
int hotelID;
static const int MAX_SIZE = 101;
Room **rPoint;
[Code] ....
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May 2, 2013
When I try to assign strings to a double pointer, it only prints out the last string when I try to print everything out, and then it segfaults.
Code:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>
main(){
char **test = calloc(3,sizeof(char));
[Code] .....
Am I assigning something the wrong way? Also, I am trying to avoid using array notation in order to practice, at least for the assigning of the strings.
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Apr 22, 2013
I have a double pointer, and I need to read words into it. Here's what I have so far:
Code:
while(fscanf(keywordFile,"%s",keyinputter)==1){
keys_cnt++;
}
keywords = (char**)calloc(keys_cnt,sizeof(char));
[Code]....
keyinputter is an array of size 30. The first while loop finds the number of words in a file so that I can calloc the correct amount of space for the double pointer, keywords. The second while loop is supposed to read the words into the double pointer, but when I run a print statement to print the string at keywords[0], it only prints null and not the word. Am I assigning the strings to the double pointer in the wrong way?
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Aug 1, 2013
How to initialize double pointer array..?
int (**aLines)[2];
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Mar 29, 2015
I'm using some overloaded operators (addition, subtraction and variants of) in part of my final major project and, when coming to test it, I've noted that they appear to be killing my pointers eventually.
I say pointers, it's always the same one. But I have isolated it to being the operators. The only two I'm really using are += and -=, though I've defined the others for consistency.
Either A ) what it is I've done wrong (if I have) or B ) why I would see this behaviour. Or, you know, if there's something glaringly obviously wrong with the code that I'm glossing over.
Code is as follows
#pragma once
#include "stdafx.h"
namespace gunpei {
/**
A paired register in the form of r1r2
Enables using two separate arrays for register processing
provides logic for assembling pair and breaking back into individual registers
*/
class GBPairedRegister {
[code]....
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Mar 1, 2014
Why do most C examples pass a double pointer when manipulating linkedlists? Why can not we just pass a single pointer to the struct?I think using an external reference accessor for a linked list would be a more appropriate solution, yes or no?
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Nov 30, 2014
The following code compiles and runs fine till it reaches line 16 and gets a sigsev violation which I'm not sure about as to why. I have no problem passing the object of type node** into the constructor of base and storing it into the double pointer node** copy;; but when I call the function void pass(node** temp) it crashes.
#include <iostream>
class base;
class node {
private:
node** data;
public:
[Code] .....
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Mar 30, 2013
i am trying to create the assignment operator for a class that uses a pointer for it's private variable. The error is saying expected constructor, deconstructor, or type conversion before "operator. (which is the assignment operator. I have tried everything i could think of or find online and nothing has worked. below is the code for the assignment operator in the .h file and the .cpp file.
//Assignment constructor
indexList &operator=(const indexList <T> &rhs);
template <class T>
indexList<T>::indexList operator=(const indexList <T> &rhs) {
if(this != &rhs) {
numberOfElements = rhs.numberOfElements;
[Code]...
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Mar 14, 2013
I'm trying to call a function via a function pointer, and this function pointer is inside a structure. The structure is being referenced via a structure pointer.
Code:
position = hash->(*funcHash)(idNmbr);
The function will return an int, which is what position is a type of. When I compile this code,
I get the error: error: expected identifier before ( token.
Is my syntax wrong? I'm not sure what would be throwing this error.
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Mar 15, 2015
how to accommodate double-size:8 bytes in 4 bytes pointer in 32bit system.
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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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Jul 3, 2014
Because MinGW C++ doesn't have the atod() or atoi() functions for some reason, I had to code a string to double function myself.
double stringToDouble(std::string input) {
bool isDecimal;
int decimalLoc;
double output = 0;
double n;
[Code] ....
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Feb 12, 2015
My program uses a menu that easily facilitates a person to navigate trough out it but im stuck on a part and I cant go to menu3 with the arrows (only use c code not c++)
#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <windows.h>
void sleep(long int interval) {
for(int i=0;i<interval*1000;i++);}
[Code]...
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Jun 22, 2014
I'm looking for an example of menu selection with arrow key i'dont know how to create one o think i should use CODE ASCI but what method I should follow
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Aug 25, 2013
I have created plane as floor and sphere as ball. I used physics equations to it and ball falls under gravity. Now i want to attach visual arrow to this ball which moves with it according to velocity direction. If ball bounces then direction of velocity is changed so does arrow.
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Mar 2, 2014
So I have assigned this method to each TextBox. It works fine pressing the left arrow and right arrow, but for some reason will not work using the up and down arrows. I have tested the string, using MessageBox and it is correct...the loop even proves it finds a matching TextBox. It is correct as in it displays the TextBox name it should be selecting but doesn't. I have no clue! Now the first select method is the one I want to use, I used the loop to check to see if it was even finding a match. It does find it but doesn't select it. The naming convention for my text boxes is r1c1 where the first number indicates the row and the second number is the column. There are 9 rows and 9 columns. This SHOULD be working but for whatever reason it is not. I've even put a message box inside the if statement for the up and down keypress check and it pops up when i press up or down.
private void Navigate(object sender, KeyEventArgs e) {
TextBox input = (TextBox)sender;
string nextBox = input.Name.ToString();
if (e.KeyCode == Keys.Left) {
if (int.Parse(nextBox.Substring(1, 1)) > 1 && int.Parse(nextBox.Substring(3, 1)) == 1)
[Code] ....
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Jun 3, 2012
So, I've been working on a project recently, and the only thing remaining to do is a detector to whenever down arrow key is pressed. The down arrow key can only trigger when a certain check box is checked and this will have to work with a timer either. The problem is that how to make the down arrow key press detector(I've got the check box and timer ready tho).
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May 13, 2012
I'm trying to implement this on ubuntu, to compile and run only under ubuntu.
I found 100s of other attempts at answering the general question of arrow key press in c++. Nothing solid.
Some recommend using the Readline for the functionality I am trying to implement, but I need to stay clear of GNU licences if I can for this project. And some tips only work on projects for windows machines... for example the conio library.
For linux there may be the option of using the ncurses library which I will take a look at, but I am stubborn and want to implement this myself. It should be an easy straight forward thing to do, which is why I am a bit frustrated at the moment.
Here is my test code so far.
#include <iostream>
#include <sstream>
#include <stdio.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>
using namespace std;
int main(void) {
char a;
stringstream ss;
string s;
[Code] ....
So! This works... 80% of the problem is solved. If you compile this, g++ under linux, ubuntu in my case, and run. Each keystroke reveals the correct key numbers.
q=113
w=119
when I click on the up key I get,
up = 279165
I thought, I can use this number is a if(int == '279165') to detect the up key.
I was not so lucky... this int is not behaving like an int!
So I modified the code to see it I could carry out an int operation on this number.
I added a 100000 to int i.
cout<< i + 100000;
Code:
#include <iostream>
#include <sstream>
#include <stdio.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>
using namespace std;
int main(void) {
char a;
stringstream ss;
string s;
[Code] .....
Compiling and running this, and pressing the UP key gives the following number.
100027100091100065
Some some sort of array, something like, [27][91][65].
I tried all ways to access these individual numbers, actually the third one for comparison purposes, but no luck.
For completeness sake I list the other arrows.
UP = [27][91][65]
DOWN = [27][91][66]
LEFT = [27][91][68]
RIGHT = [27][91][67]
A little further digging shows that these numbers are derived from the representation of a "multi-char" constant, the data type given when pressing special characters...
Now here is the main problem I have, I can find ANY decent documentation on how to handle and play with "multi-char" .
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Apr 27, 2013
I am doing a project for a class which involves making a game where there is an arrray that holds a player (you) and a zombie (comp). The player is suppose to be able to turn clockwise or counter clockwise, move forward, and backward and shoot. Im having trouble trying to rotate the char in an array. I am also trying to switch from using the W,S,D,A to the arrow keys but doesnt seem to work.
#include <iostream>
#include <windows.h>
#include "color.h"
using namespace std;
using namespace Petter;
const int COL = 15;
void initBoard(char[][COL], int, int);
[Code] ....
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Apr 25, 2013
ok here is the question: Write a function that will initialize a double data array element to 0.0 ?
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