C++ :: Why Not Referencing Other Parameters In Default Values Allowed
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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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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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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Jul 7, 2014
I'm asking how to create a function with default parameters with the possibility to init the parameters that you need.
Code Example :
#include <iostream>
int func(int a = 1, int b = 2, int c = 3, int d = 4) {
return a + b * c / d;
[Code] .....
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Aug 19, 2014
In the thread "Making a argument optional to function", it is stated that to set default values for arguments of a function you can simply do so in the function definition, like:
int myfunc(int a, int b, int c=3) {...}
This then automatically puts c to 3 in the function body if a call like myfunc(1,2); is made, if I understood correctly. However, this does not seem to hold for class functions. For example, something like:
class classy {
public:
int class_func(int, int, int); // class function prototype
}
int classy::class_func(int a, int b, int c=3) {...}
fails to compile. What I would like is to be able to call class_func outside of this class (by including it as a header in another macro), optionally specifying c. If c is not specified in the call, it should use a default value.
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Nov 30, 2013
Same solution that I was having compiler errors on yesterday. We're working with inheritance and the program is supposed to be to create and display information for default Employee objects, Hourly Employee objects and Salaried Employee objects. Everything compiles as is, but I'm running into two issues that I can't figure out.
1) In both the hourly and salaried objects, the wage, hours, and management level attributes all displaying their default values. I'm almost positive that this has something to do with the str to int and str to double conversions that I'm using (currently have atoi and atof in the file, but I've also tried stringstream, but still had to same problem). Any thoughts as to what I'm missing?
2) the assignment calls for the Benefit benefit member in Employee.h to be protected. However this makes the member unaccessible when I try to use it in the EmployeeMain.cpp in order to set the input for the Benefit class members. I had to make the Benefit benefit member public again to get it to compile. How would I set the input for the Benefit class members while the Benefit benefit member is protected?
Solution files follow:
EmployeeMain.cpp
Code:
#include "Hourly.h"
#include "Salaried.h"
void DisplayApplicationInformation();
void DisplayDivider(string);
string GetInput(string);
[Code]....
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Oct 11, 2014
I would like to write a program that gives you a few default values. Now you can keep these values by pressing the enter key or you can change them by just typing in new ones and confirm the new values by pressing the enter key again.
Thats as far as i got on my own but it doesn't really work. what i can do to fix this.
Code:
#include<stdio.h>
#include <conio.h>
int getInt(int min, int max);
int main () {
int a[3] = {3,4};
int b;
int code;
[Code]...
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Feb 2, 2013
Is there anyway we can return 2 values from a called function. Example
Code:
float xxxx(float a, float b, float c, float d)
{///
///
///
}
void xxx() {
int e,f,g,h;
////
////
xxx(e,f,g,h);
}
So if I want for example a+b and c+d, can i return those 2 answer? I don't think its possible since I am new into C programming.
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Feb 9, 2015
I'm fairly new to C++ and programming in general and I'm trying to get a program to check the parameters of a binary string before converting that string to dec values. I have the user input 'num' line 39 - 42, but I want to reuse that same value in the 'void bin_to_dec()' function. Is there anyway I can use the same variable between void functions?
13 #include <bitset>
14 #include <sstream>
15 using namespace std;
16
17 void dec_to_bin(){
18 string mess;
[Code] ....
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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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Jul 22, 2013
#include<iostream>
#include<cstdio>
#include<list>
[Code]....
In the last line "graph.edge{x,y,w}" it says typename is not allowed? I have used nested class edge and pushing vertices and their weight in elist vector which is of type edge.
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May 8, 2013
I am trying to get a program to take two files and place them into a third file. I have searched all over this website looking for a solution and i can seem to find one.
My issue is that i keep getting an error 'incomplete type is not allowed' as well as 'no operator matches these ">>" these operands.'
#include<iostream>
#include<string>
#include <sstream>
using namespace std;
int main() {
string filename1;
[Code] .....
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Jul 19, 2012
So, I ran into the above error. I can't post the actual code, but here is the setup... I have four classes: A, B, C, and D.
A.hpp
Code:
class A {
public:
virtual void foo( D& bar );
[Code] .....
In A.cpp I implement foo and use bar in a similar manner as shown in class C. The difference here is that in A.cpp I also include the header for the D class. I am a bit confused why I can pass bar to B::foo() and that works fine, but if I try to access bar in C::foo, I have issues. Currently I am just including D.hpp in C.cpp.
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Sep 30, 2014
I have an enum like:
Code:
typedef enum mac_type_e{
STATIC_MAC,
BLACKLIST_MAC
} mac_type_t; and I want to use this type in a structure that's declared like:
Code:
typedef struct lan_mac_s {
UINT16 lanmacid;
enum mac_type_t lan_mac_type_pp;// user mac type per port, 20 mac_type_t array, 0 = static, 1 = blacklisted now,
The compiler tells me:
Code:
incomplete type is not allowed
enum mac_type_t lan_mac_type_pp;// user mac type per port, 20 mac_type_t array, 0 = static, 1 = blacklisted
But if I remove the preceeding "enum" keyword, it compiles fine.
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Feb 15, 2013
this is my header file
#ifndef Header_H
#define Header_H
#include <iostream>
#include <string>
using namespace std;
class CurrentAccount{
[Code] ....
The problem i m facing now is the CurrentAccount class display is showing error inherited member is not allowed....
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May 26, 2014
When declare and assign an instance of a user-defined struct in a function. And the struct (theStruct) is not declared in the same header file as the function (theFunction). Like this:
files:
"A.h": declares the struct in a class (theClass)
"A.cpp": implements the struct
"B.h": declares the function
"B.cpp": implements the function, error here
I think making the instance (inst) a reference might solve this. But the instance is assigned to a return value from a function (returnFunc). Like:
void theFunction() {
...
theClass::theStruct inst = returnFunc(...);
//returnFunc() returns an instance of theStruct
//the error is at 'inst'
...
}
What do you think?
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Feb 13, 2014
I'm going from section 7.1 where it is stated that:
Standard wrote:A declaration occurs in a scope (3.3); the scope rules are summarized in 3.4. A declaration that declares a function or defines a class, namespace, template, or function also has one or more scopes nested within it.
Jumping to section 3.3 we find that there exist block scope, function prototype scope, function scope, namespace scope, class scope, enumeration scope, and template parameter scope.
I find nothing that states that static_assert declarations cannot be used in any of those scopes, yet only block, function, class, and namespace scopes allow for it with clang.
static_assert(true, "");// namespace scope (good))
class X {
static_assert(true, "");// class scope (good))
[Code].....
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Jul 19, 2014
I have made a datagrid in a WPF and added a button to add rows, here is the code for that:
this.itemListDataGrid.Items.Add(new TextBox());
Also, I have already got 3 colums in the datagrid pre-added by me, so when the rows are added I click on one to edit it and it comes up with error edit item not allowed.
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May 21, 2013
Code:
#include "..ObjectsObjects.h"
class Idle;
class Objects;
class Goods;
[Code].....
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Mar 1, 2013
I have a function like this
void foo( int i) {
...
uint8_t buf[ i];
...
}
And I don't understand why the compiler is not complaining... I'm using g++ -c -g -Wall to compile ....
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