C++ :: Using Initializer List As Function Parameter
Nov 26, 2014
#include <iostream>
#include <initializer_list>
using namespace std;
void doSomething(std::initializer_list<int> list) {
} int main() {
doSomething({2,3,6,8});
return 0;
}
I write a small piece of code like above. But I can not compile it successfully. I try it both with and without the line "using namespace std", but nothing worked.
The error list: Symbol 'initializer_list' could not be resolved
I use Eclipse CDT and GCC 4.9.1.
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Jan 11, 2015
Is there any function which can return parameter list of a function.
For example : get_param(f(int x,char y )) return parameter x-> int y-> char
and f_name ->f
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Jan 22, 2014
Is there some way to generate an initializer list algoritmically?
In the case I'm thinking of, I want to initialize a map<> to pair<key, constant> over all expected values of key.
Obviously i could write a loop to initialize after construction, but it would be nice if it could be done in one statement.
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Jan 4, 2015
In order to test catching exceptions from an initializer list, I deliberately did bad practice by hard coding an argument to a ctor that would cause a std::bad_allocto be thrown. Obviously better practice is to send a variable, but that would cause a compile error, so I hard coded a value.
The program I wrote creates Prime Numbers up to a specified limit which is an argument to the ctor of type std::size_t. The program works fine IMO, using g++ in cygwin:
$ time ./PrimesExe
Limit is 2000000
148933 Primes Created
real 0m1.210s
user 0m1.123s
sys 0m0.046s
Now when I send something invalid like a negative number or something too big for std::size_t, the program seems to run indefinitely, when compiled with g++ under cygwin. I haven't tested it yet on Linux.
However, if I do the same on VS2013 express, it takes about 15 seconds to print the expected caught exception message. I was not expecting it to take so ridiculously long compared to the reasonable amount of work involved in doing primes up to 2 million.
I have read up about what is involved in catching exceptions: stack unwinding, keeping track of what needs to be destroyed etc. But this is 1 object with 1 ctor argument, no Base classes or any other complications. So why such a long or indefinite amount of time?
This whole example is probably contrived, and I am wondering whether exceptions is the right tool for this - it is similar to the divide by zero problem, or could be considered a programming error to call a ctor with a bad argument?
Also, catching an exception thrown by an initalizer list seems a bit awkward in that one seems to have enclose the creation of the object and all subsequent uses of it (and any code in between ) in the same try block, otherwise it goes out scope. I suppose I could try to write a wrapper function that returns a smart pointer reference to a valid object, but I would have to test the validity of it's return too. That's the awkward part - there is probably a better way?
Are there any recommended ways of recovering from initializer list exception, that is, to allow the user to enter a new hopefully valid value and try to create the object again?
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Oct 21, 2013
I have a project that compiles fine with VS 2010. As I compile it with VS 2012 it generates the entitled error. Why?
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Aug 27, 2013
The below code is taken from the open source 7zip project (7z920CPP7zipUIFileManagerBrowseDialog.h)
Code:
class CBrowseDialog: public NWindows::NControl::CModalDialog {
What does the single colon (CBrowseDialog:) mean? Is that Initializer List?
I know the double colon (NWindows::NControl::CModalDialog) is Scope Resolution Operator.
Why is (: public NWindows::NControl::CModalDialog) used with the class declaration?
Similar code is found through out the project along with class declarations.
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Sep 28, 2014
My errors are at the end of the program in two function calls within the definition of the InsertByValue function. g++ does not seem to recognize NumArray as a valid parameter.
#include <iostream>
#include <assert.h>
using namespace std;
const int CAPACITY = 20;
/* Displays the content of an int array, both the array and the size of array will be passed as parameters to the function
@param array: gives the array to be displayed
@param array_size: gives the number of elements in the array */
void DisplayArray (int array[], int array_size);
[Code] ....
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Jul 6, 2014
error says "cannot convert 'int*' to 'int' in function main()
and also
type mismatch in parameter in function sort(int,int)
Heres the code:
#include<iostream.h>
#include<conio.h>
void main() {
void sort(int,int);
clrscr();
[Code] .....
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Oct 28, 2013
I have a class as below:
// RemoteControlMonitor.H
typedef void (*keyaction)(unsigned int key);
class RemoteControlMonitor {
private:
keyaction rph;
keyaction rrh;
[Code] .....
But I got compile error as below:
RemoteControlMonitor.H:58: invalid type `void *' for default argument to `void (*)(unsigned int)'
rcx1.C: In function `void __static_initialization_and_destruction_0(int, int)':
rcx1.C:54: ANSI C++ forbids implicit conversion from `void *' in default argument
What can I do?
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Apr 17, 2014
How I can delete a parameter in a function .
int *buildTrail(int antIndex, int start, double *pheromones) {
int *trail = new int[tabu];
bool *visited = new bool[tabu];
trail[0] = start;
visited[start] = true;
[Code] ....
If I comment all lines includes visited word , no exception occurs , Otherwise , exception throws.
Simply put , How can i delete visited parameter as long as its role has been finished?
.
.
.
delete visited ;
return trail;
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Jan 7, 2015
gcc v.8.3 -std=gnu++11
[URL]
I'm trying to pass a function as a parameter and failing. It seems simple, until I get the error messages.
Here is the code:
class MinimalSolver {
typedef double (*func)(double sum, double char);
void driver();
[Code]....
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May 17, 2013
void foo(FILE *f1, FILE **f2) {
fputs("...", f1);
fputs("...", *f2);
} int main(void) {
FILE *fp1 = fopen(...),
*fp2 = fopen(...);
if(fp1 && fp2) {
foo(fp1, &fp2);
...
}
...
}
Forever, I've passed FILE objects into functions like the first parameter; I've never had an issue reading or writing files using that form - no file errors, no compiler warnings, etc. Recently, I saw the second parameter form, and wondered why that was?
I still don't quite get this part of pointers. What's the second parameter form doing differently than the first when the first version *appears* to work as intended??
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Oct 6, 2014
How come when we pass an array as a parameter to a function, the entire array is copied and is available to function?
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May 2, 2013
Write a program that inputs 10 integers from the console into an array, and removes the duplicate array elements and prints the array. By removing, I mean that you should make it appear as if the elements hadn't been there. You may assume that all the integers are between 0 and 100, Write at least 1 function in addition to the main function, and pass an array into that function as a parameter. e.g.
Please enter your 10 numbers: 1 2 3 4 5 6 7 8 9 10 The array contains: 1 2 3 4 5 6 7 8 9 10
Please enter your 10 numbers: 1 1 3 3 3 6 7 8 9 9 The array contains: 1 3 6 7 8 9
Please enter your 10 numbers: 1 1 1 1 1 1 1 1 1 1 The array contains: 1
The bolded area is where I'm having trouble. How I can go about doing this, passing an array into the function as a parameter?
Here is my code:
#include "stdafx.h"
#include <iostream>
using namespace std;
int main () {
const int MAX = 10;
int a[MAX] = {0};
int i;
[Code]...
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Dec 26, 2013
Pseudocode:
template<typename T /*, some parameter for member_function */>
class Foo {
public:
void someFunction() {
T t;
t.member_fuction(...);
} }
I'm trying to make the call to T::member_function a templated value because member_function might vary by name in my scenario. Since std::mem_fn isn't a 'type', i can't do something like Foo<std::string, std::mem_fn(&std::string::clear)> foo;
I also want to take into account that member_function might have more than one parameter. That is, the first parameter will always be something known but there might be other defaulted parameters.
The only thing I can think of is to make a proxy structure, something like this:
template<typename T, T> struct proxy;
template<typename T, typename R, typename... Args, R (T::*member_function)(Args...)>
struct proxy<R (T::*)(Args...), member_function> {
R operator()(T &obj, Args.. args) {
return (obj.*member_function)(std::forward<Args>(args)...);
} }
Which would then allow me to do (for example) this:
Foo<std::string, proxy<void(std::string::*)(), &std::string::clear> >
when Foo is implemented like this:
template<typename T, typename member_function>
class Foo {
public:
void someFunction() {
T t;
member_function()(t);
} };
That implementation works for me.
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Sep 11, 2014
is it true or false
a function like void myfun(int num){} can receive type "int var" but can't receive type "const int var"
AND
a function like void myfun(const int num){} can receive both type "int var" and also type "const int var"
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May 2, 2013
I have been working on this all day, and its due in like an hour and a half. I have done everything the program wants except the last part. Here is the assignment:
Write a program that inputs 10 integers from the console into an array, and removes the duplicate array elements and prints the array. You may assume that all the integers are between 0 and 100, Write at least 1 function in addition to the main function, and pass an array into that function as a parameter. e.g.
Please enter your 10 numbers: 1 2 3 4 5 6 7 8 9 10
The array contains: 1 2 3 4 5 6 7 8 9 10
Please enter your 10 numbers: 1 1 3 3 3 6 7 8 9 9
The array contains: 1 3 6 7 8 9
Please enter your 10 numbers: 1 1 1 1 1 1 1 1 1 1
The array contains: 1
The bolded part is what I cant get to work. I have tried this and it keeps telling me I have not identified the items when I have.
Here is my code:
#include "stdafx.h"
#include <iostream>
using namespace std;
[Code]....
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Oct 20, 2013
How can I pass a function as a parameter? I have a class that I'm trying to reuse and one of the methods in this class need to take three parameters, two ints and a function. In other words I want to be able to call a custom function every time this method is invoked when used in other classes. The function I want to call will not return any values, its a void function.
In my Class:
void Utility::someFunction(int var1, int var2, void customFunction) {
int num1 = var1;
int num2 = var2;
[Code] .....
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May 30, 2013
I'm making a code that uses a Function pointer. The problem is, when I try to compile appears an error like:
error: no matching function for call to 'rnVector::rnVector()'
Here's part of the code:
phiFunction::phiFunction(double (*f)(rnVector), rnVector (*df)(rnVector)) {
//... Here comes the code stuff...
}
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Sep 25, 2012
I created the following code to pass the the variable 'inputVoltage' by reference to the function 'input'. It certainly works when I run the program, but I dont think it is a standard way of doing it, i.e. the use of '*' and '&' is not according to convention ? Or perhaps the way did it is acceptable ?
int input (double *inputVoltage);
int main ( {
double inputVoltage;
input(&inputVoltage);
[Code]....
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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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Oct 18, 2014
I'm writing a small function that gets as parameter a file's path and a folder's path, and copies the given file to that folder.
Code:
int copy_file(const char* source, const char* folder) {
char copy[PATH_MAX];
strcpy(copy, folder);
strcat(copy, "/");
strcat(copy, source);
[Code] ....
Basically, this function purpose is to make a backup of source in folder every X minutes (depending on user's input).
The problem is the second call to open():
This call attempts to open the file for writing, and creates it if it is not already exist.
It also truncates it before writing to it - and that's my concern:
Let's say this is the second time this function runs, so copy is already exist. open() will then truncate it, and then one of the system calls in the while loop fails.
In this situation, I might be left with no backup file.
The problem also arises for when source is a read-only file:
If source is a read-only file, and copy is not already exist (meaning - it's the first backup attempt), then everything's fine, but, if source is a read-only file and copy is already exist, then I have to first remove copy altogather, and make a fresh copy of source.
Making a backup with new name for copy every time copy_file() runs, will solve this problem, and how can this be accomplished?
I should say that I'd really prefer that copy and source will have the same names when copy_file() returns...
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Feb 23, 2015
I just want to call the function : outputboo(), but I dont know how
Code: /*Enthusiastic
Pessimism
desensitize
uniqueness
*/
#include <stdio.h>
#include <string.h>
struct Books{
char title[50];
char author[50];
[Code]...
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Dec 8, 2014
I have some code here where I try to declare a struct then pass it as a parameter into a function to do something to it:
Code:
struct _user {
char * initial[3];
int pos;
} user;
int initial_add (struct user * initial_list, int initials, char * buffer) {
[Code] ...
I get the error :
server2.c:15: warning: "struct user" declared inside parameter list
server2.c:15: warning: its scope is only this definition or declaration, which is probably not what you want
[Code] ....
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Oct 26, 2014
I need to design an interface(a function prototype) that takes an argument which is used to pass information.
The information can be passed by independent modules and third party softwares and hence can vary today and in future.
Basically, the function interface(arg1, info)caters a niche service to many independent applications and needs to process based on requirements passed by applications in the argument(info, in example).
I am looking for a design pattern for the function parameter - info.
Should I use a void pointer that can be casted to respective application specific class in the function ? will this be a good C++ design ?
or should I take this parameter to be a pointer to a generic abstract class that points to the respective application specific specialization ?
Do we have some design pattern to address this so as to handle other unforeseen challenges ?
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Dec 31, 2013
I have a function (name Callback), with take some parameter( name Arg). I want to create it before, pass it to other class ( class B). And in class B, call the Callback function with Arg paramater. It's something like this:
class A {
void A::doSomething(int a, bool b){//dosomething};
void A::setCallback(B b) {//I don't know how to do this};
[Code].....
How can i do this? And what happen with I want B can get more type of callback function, which mean I don't know the type of Callback's paramater?
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