C++ :: Difference In By Referencing And By Pointer In Parameters?
Aug 6, 2013
void func(float arg); // arg is supposed to be in type, with no referencing, just a copy of it
void func(float &arg); // arg is supposed to be in, out type, with something contained in it already
void func(float *arg); // arg is supposed to be in-out type, with nothing contained in it already and can be NULL
void func(const float& arg) // arg is supposed to be in type, with nothing contained in it already and cannot be NULL
Am I all correct?
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Nov 24, 2013
[URL] ....
#include <iostream>
#include <vector>
void f(std::vector<int> const &v, std::vector<int>::const_iterator it = v.end()) {
} int main() {
f({}); }
prog.cpp:4:73: error: local variable ‘v’ may not appear in this context
void f(std::vector<int> const &v, std::vector<int>::const_iterator it = v.end())
Why is this not allowed? (I mean, what is the reasoning for defining the standard this way?)
In C++14/C++17 we will have a unified way to represent end iterators without an instance of the container, but currently I just have to hope my implementation accepts a default-constructed iterator as an end iterator.
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Jan 21, 2013
I just figured out that some std functions (for example: copy) need the resource and target objects have iterators to work. Otherwise, the compiler rejects. In case of two arrays, declared as:
double myA[100] = {};
array<double, 100> myB = {};
myA[0] is like a pointer, myB.begin() an iterator, if I do not make any mistake. So, what is exactly the difference between the pointer and the iterator here? They all give the access to elements.
If I need the target of copy to be an array like myA which cannot give an iterator, is there a way to make the command "copy" work for it?
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Jan 30, 2013
Here is the assignment: (3pts) Given the following class header file, write the class’ source code for each of the accessor and mutator functions listed. (How the functions have listed their parameters, varying between passing by reference and by value.) Don’t forget to comment your code – it counts!
class Album {
private:
char * artist; // band or singer’s name
char * title; // title of the album
[code]....
The input will be an array. My questions: First, am I on the right track?
When using (char * a) for a function, for example, this is passing the address of a, correct? so then *artist=a; changes what the address of a points to?
also, the functions are bool when I would expect void. Why? for all of the set_" " functions, the parameter is *... but for set_record_label it is *&. That appears to be a mistake to me. Is that right?
what is the difference between *& and * as parameters?
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Jul 12, 2014
I've read about the difference between the two, what one can do that the other can't syntactially, but I'm still very confused by the concept of references in C++. I'm trying to understand what is the difference in terms of undelying implementation.
Take, for example, the following code:
void foo(int *bar) {
++*bar;
}
int main(void) {
int n = 0;
foo(&n);
return 0;
} Translated into: Code: __Z3fooPi:
[Code] ....
Considering the above assembly code, and the memory that was used in both cases, I'm tempted to say that references was added to C++ to make the synax looks prettier... Where would I be wrong?
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Jan 24, 2013
What is the difference in pass by pointer and pass by reference? As per my understanding, there is no difference much.If a function accepts pointer, then NULL check can be performed.other than this i'm not able to see any big difference..
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Mar 9, 2013
i'm still unclear between the difference between using pointer and a reference
I understood the concept of pointers in c in the class i took last year
and that was to change the actual value stored in the memory address Code:
void change_a(int a*){
a=6;
}
int main(){
int a=5;
change_a(&a);
}
but in c++ I've been using references in all my assignments because I don't know how to correctly use pointers in c++ I may have missed a class but I'm on spring break and would like to clear things up
so in c++
in my assignments I would call it like this Code:
void change_a(int &a){
a=6;
}
int main(){
int a=5;
change_a(a);
}
so does this change the value in the address or does it make another copy of a in my c++ code and stores 6 in that copy
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Aug 30, 2014
whats the difference between functions as pointer and normal function, eg:
void function1(void)
void *function1(void)
What is the difference between the two?I'm doing parallel programming and we use pointer functions (void *function1(void)) when calling threads. I want to why it is done.
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Mar 16, 2013
What would be the correct way to call a function within main that has file pointer parameters?
function prototype: Code: void CalculateBoth(int num1, int num2, int*sumPtr, int *diffPtr);
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Jul 30, 2013
My problem is as following.
I have an 2 arrays named: abee1 , abee2.
I have loop that want to call them one by one and print data of an them in each step. It means that I want to reach the name of arrayBee1 to arrayBee2 in the loop for printing its data. I made the name of each one by using strings ( abee1 , abee2) in the loop.
#include<iostream>
#include<string>
#include <sstream>
using namespace std ;
int abee1 [4] [4] = {{5,0,40,30},{6,0,21,47},{7,0,17,63},{8,0,31,62}};
int abee2 [4] [4] = {{1,0,37,52},{2,0,49,49},{3,0,52,64},{4,0,20,26}};
[Code] ....
I know something is wrong with the "string *a = & arrayname;" part of code and after that.
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Mar 24, 2015
concepts on pointers to structures and referencing for the following two lines.
//address of the variable "struct UIP_IP_BUF" is assigned as srcipaddr
uip_ds6_nbr_add(&UIP_IP_BUF->srcipaddr,
//data type "uip_lladdr_t" pointer points to the address of array an "nd6_opt_llao" with size UIP_ND6_OPT_DATA_OFFSET
(uip_lladdr_t *)&nd6_opt_llao[UIP_ND6_OPT_DATA_OFFSET]
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Aug 17, 2014
I am building a log4net wrapper project where I reference log4net.dll. When calling this code through a static instance to log messages the new project also wants me to reference log4net.dll even though I have a reference to my logging project which in turn has the reference..
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Oct 23, 2014
I need to return taxes paid and net pay by pass referencing a gross pay overloaded function. Are the values returned from calling the overloaded function file stream objects? Can they be passed simply through a pass-by-reference function?
//Read Data from File, gather info and calculate pay, output data to file
while(counter < x) {
inFile >> last_name >> first_name >> hours_worked >> hourly_pay;
outFile << first_name << " " << last_name << " ";
outFile << calculate_gross_pay(hours_worked,hourly_pay);
counter++;
outFile<<endl;
[code].....
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Oct 4, 2014
We had to convert a single-line text editor which uses arrays to one that uses OOP and double-linked lists and I have been doing it in steps. I have, for the sake of convenience, put my headers, implementation and main all in one file.
I'm compiling this program in Hercules (the getch function uses C code).
I keep getting the error from the compiler saying "Undefined Symbol" for functions:
insertNode(char, Node);
deleteNode(Node*);
insertHead(char);
The full message is: ld: fatal: Symbol Referencing Errors. No output written to a.out collect2: ld returned with 1 exit status.
// A fake single line text editor program.
#include <stdio.h>
#include <iostream>
#include <cstdlib>
#include <unistd.h>
#include <termios.h>
//#include "main.h"
typedef char Letter;
[code]....
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May 8, 2014
Basically I have a few tables in my Database.
So I have one table that is like so:
Item_ID, Name, Parent ID.
1 , jeff , 5
and another table like this:
Parent_ID, parent_Name
5,jackson
What I would like to happen, when I run my code is that I'll get the following
Item_ID, Name, parent_Name
1 , jeff , jackson
DataSet DS = new DataSet();
if (this.OpenConnection() == true) {
mySqlDataAdapter = new MySqlDataAdapter("select Item_ID, NAME, Parent_ID from table1, table2", connection);
mySqlDataAdapter.Fill(DS);
dataGridView1.DataSource = DS.Tables[0];
//close connection
this.CloseConnection();
}
So this spit out parent ID = 5.
I've not worked with Dataset before and I was just wondering what is the best approach? Can this be done via a SQL command or will I have to replace the value(5) with the string(jackson) using a large IF loop to search and replace.
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Feb 9, 2014
I have code working, but that is largely because a vector that I am using as part of a structure that is the first of two elements of a MAP (with the second being an integer that is assigned later) is serving in its original, purely vector form, to fill out a set of selections on a DOS screen (option 1, 2, 3, etc.).
I do use the MAP, because it is a simple means of referencing the integer value using a word that is part of the structure, and is probably appropriate, saving me a search through the vector of words and calling up the value at the same location in the vector of words in a vector of corresponding numerical values. I DO feel that what I'm doing to produce the selection list is something of a "cheat" because I do not know how to access the same data within the structure component of the MAP by simply using a similar numerical reference (e.g. "MAP[1].structure.word", or would that be "MAP.structure.word[1]" ????) to print out the words in the structure in the map as choices on the screen.
I don't want to change or expand the contents of the map, just access and print each one in a simple loop with a number from the loop counter to the left of each word.
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May 15, 2014
I am creating sets of list for rotational schedule. I read that to create a randomizer is by using Randomize() function. What i want to ask is how do you set the parameters? what function should i use?
for example:
1. there are three list of the same type.
2. the range are 1-100 and a-z. (can i use 1-100 instead of writing all of the range?)
3. i need seven of each range (example: 3, 42, 78, 11, 89, 64, 22, a, n, y, e, t, d, j) for each list.
4. the three list will be generated 52 times
5. (this is the hardest part) the range must be distributed equally first, before repeating the range. For example: if the number 4 is to be used again, it must wait for other number to be on the list. The same goes for the alphabet.
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Nov 21, 2013
What's the problem with the following:
Code:
#define K 3;
int max(int a, int b) {
return a>b? a : b;
} int main() {
cout<<max(K, K+3);
return 0;
}
Why is it not allowed, and how is it different from:
Code:
int max(int a, int b) {
return a>b? a : b;
} int main() {
cout<<max(3, 3+3);
return 0;
}
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Jun 30, 2013
How can i upgrade my program I want to input a octal and binary number and convert them in base 2, 8, 10, 16..
how can I write the scanf with the right parameter in it??
Code:
scanf ("%x",&i); Code: #include<stdio.h>
#include<conio.h>
#include<stdlib.h>
int main() {
int i;
char buffer [33];
[Code] .....
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May 9, 2013
I've been using threading for a while, that was no needing parameters. so I used for example the following line :
_beginthread(functionName, 0, (void*)10);
and it worked great...
but now I have a function that has an int parameter (int num), and I dont know how to transfer it using _beginthread...
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Mar 16, 2013
I have developed an application in C++ that creates some text files in a directory chosen by the user.
How can I ask the user set a Default Directory Path (and some other default parameters) so that she doesn't have to enter the same data in the GUI everytime the application is run.
The application has been developed using Qt Creator.
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Oct 14, 2013
how would I pass this parameter and how/why is it not working this way? I've tried many different methods to this and I can't quite seem to figure it out.
studentList student;
student.push(252875, "Jerry", "UTPA");
What I thought would work
class student {
public:
int id; //student ID number
string name; //student’s name
string university; //student’ university
};
//student list is a doubly linked list of students.
[code]....
My header file.
I am honestly not sure where to start here. I would assume that it would know what to do with the varibles but it doesn't seem to want to accept them. It gives me
Error1error C2660: 'studentList::push' : function does not take 3 arguments
2IntelliSense: no suitable constructor exists to convert from "int" to "student"
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Mar 19, 2015
im actually doing a authentication system, it will start console with
Username:
Password:
and do things but i want to know how can i give my program any parameters? i mean when im launching my program i want to do exactly this:
"C:UsersSpravcaDocumentsVisual Studio 2013ProjectsConsoleApplication14ConsoleApplication14inReleaseMyApp.exe" -registration
I tried to google "c# program parameters" && "c# program argues" but i couldnt find anything, maybe i just dont know how is exactly this named?
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Jan 24, 2015
In my program I created three separate return functions. Each function is labeled:
int boxes(int x, int y);
int leftOver(int x, int y);
double avgItemsShipped(int x, int y, int z);
Is it bad programming practice to use 'x' and 'y' in all of my functions? Should I use the this keyword inside the function? We use this often in my Java class and I know it exists in C++, but I haven't actually seen it used (or used it myself yet).
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May 28, 2014
I created 3 Rectangle pointers. And later in the program, I would like to modify these existing Rectangles by calling constructors with parameters. Is this possible? I have a sense that it involves creating overload operators, but I am not sure how to do it, or if that's the correct path.
#include <iostream>
#include <string>
using namespace std;
// Base class
class Shape {
protected:
int width;
int height;
[code]....
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Aug 4, 2014
I have class that have member variables which is also a class object that contains member variables which is also a class... so on and so on... like this
Code:
class Device
{
public:
Device();
[Code]...
When i create a device object, i want to be able to initialize all its member variables, such _data, _value, but since Data has also a set of members need to be initialized, i also need to pass parameter like Record, Type, Test etc to Device constructor, all down to the primitives level of member variables of all its embedded classes object... the top level class constructor may need a very very long list of parameters....depending on the number of member variables each embedded class contains! I know i can break down the initialization process, but i prefer to do a one line initialization, without much objects copying etc... and i use scoped pointer where it need to be initialized just once. Is it common to code a constructor with long list of parameters??
Code:
Device::Device(double deviceValue, int countPlayers, int NumRecord, int DataType, double dataTest)
{
_data = QScopedPointer<Data> (new Data(NumRecord, countPlayers, dataType, dataTest));
_value = deviceValue;
}
[Code].....
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