Does putting a ref when passing a struct to a parameter work? Say i have this code
struct struct1 {
public int i;
public void show() {
Console.WriteLine(i);
[Code] ....
The output doesn't change. The result is
0
100
500
0
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]....
Basically I'm trying to pass an object as a reference to the template function, rather than a copy as it's seeing. I'm needing to do this without editing Obj::Call to accommodate a reference as its first parameter, as it'd break other calls.
You'll notice in the following code the object will be destroyed upon passing, while the object defined is still in-scope due to the infinite end loop.
#include <iostream>
#include <string>
using namespace std;
class Obj {
public:
string name;
Obj(string name): name(name) {cout << "create " << this << endl;}
[code]....
In the past I tried ref(), which appeared to stop this happening, however it created a blank copy of the object instead.
I am trying to make a automated menu. It shows there are no syntax errors but when compiled it says cannot convert choice from type into to menuItemType. I am not sure what I did wrong. Here is the code
Code: #include <iostream>
#include <string>
#include <fstream>
using namespace std;
struct menuItemType
{
string menuItem;
[Code]...
I am working on incorporating a function in to an already existing piece of code, I have incorporated the function fine as far as I am aware.
The problem I have is that I am trying to pass two int arrays to the function, so that i can manipulate and compare them "the values will be changed the originals cannot be changed"
I am having trouble pulling the information out of the already created array, I am able to pass the pointer reference for the single value which is not exactly what i want "best_prog".
My function is below I have commented the memcpy parts and also the majority of the code isn't there cause it is not needed to see make the copy work.
int edit_distance(int index) {
struct prog *progp = &population[best_prog];
/* The struct of best prog not sure if i need one for the other prog I am trying to compare it with the one below doesn't work as intended.*/
//struct prog *progp = &population[];
int editdistance = 0, ar1 = 0, ar2 = 0, a = 0, b = 0, j = 0, x = 0;
[code].....
I am writing a text-based rpg and I'm having some issues trying to pass the player struct to a function. First, here are the relevant code snippets. Also, Player.c and Player.h aren't completed but the relevant function is. I just run tests every now and then to see if everything is working right.
Monster.h
#ifndef MONSTER_H
#define MONSTER_H
#include "Weapon.h"
typedef struct Player;
typedef struct {
char* mName;
[Code] ....
The errors are:
1. line 33 in Monster.h, the void Attack_Monster_Types(Monster* m, Player* p) the ide says missing ')' before '*', missing '{' before '*' and 'Player' name in formal parameter list illegal
2. line 18 in main.c when the attack function is called. it says 'Attack_Monster_Types' Undefined; assuming extern returning int.
I believe I have all the right headers included so I'm not sure what to do ....
Due to the nature of this requirement, I've made a very minimal example, which would adequately solve my issue, without resorting to use of pointers or copy constructors.
Basically I'm trying to pass an object as a reference to the template function, rather than a copy as it's seeing. I'm needing to do this without editing Obj::Call to accommodate a reference as its first parameter, as it'd break other calls.
You'll notice in the following code the object will be destroyed upon passing, while the object defined is still in-scope due to the infinite end loop.
#include <iostream>
#include <string>
using namespace std;
class Obj {
public:
string name;
[Code] ....
In the past I tried ref(), which appeared to stop this happening, however it created a blank copy of the object instead.
Code:
#include <stdio.h>
void ASCII_to_EBCDIC( size_t, unsigned char *);
void EBCDIC_to_ASCII( size_t, unsigned char *);
void to_ASCII(unsigned char *);
void to_EBCDIC(unsigned char *);
/* conversion tables */
static unsigned char
[Code] ....
The above snippet is for a buffer/string, where as i want to pass file name as a parameter and want function to process the file line by line?
#include <cstdlib>
#include <iostream>
struct tax_node {
char form; // tax form letter
int version; // tax form number
[Code] ....
I cannot seem to get why function print_contents will not work. The couts at the end of the program is just to test that it printed correctly. But, if I need it to print the contents such when print_contents(ptr2) is called. I think it should be tax_ptr in the parameter list but I am not quite sure.
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]....
I want to create events and then, functions which are subscribed to the event can access information about the event. For example, in Class 2 below, I want it to be able to access things such as touch.position, etc. of class 1.
Class 1:
public delegate void TouchEventHandler (EventArgs e);
public event TouchEventHandler TouchBegan;
public Vector2 touchPosition;
void Update () {
if (Input.touchCount > 0) {
[Code] ...
Class 2:
void OnTouchBegan (EventArgs e) {
Debug.Log ("Ran");
}
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]...
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] ....
I have a school project in which need to create a function that takes a File Object as a Reference Parameter. Supposedly, it should allow me to read the first piece of data from others separated by a space from a file. The later be able to continue reading from the next piece of data.
I know how to set things up to read from the data file, such as using
Code:
#include <iostream> , and
Code:
ifstream inputFileName;
inputFile.open ("nameOfFile");
I also understand how to pass a variable by reference to a function. But I simply cannot put the two items together!
I tried using
Code:
void getFileInput (ifstream &); //parameter
getFileInput ("nameOfFile") // call
void getFileInput (ifstream &dataFileName)
In the function I used
Code:
ifstream inputFile;
inputFile.open (dataFileName);
I'm just not getting an understanding of this concept!
How come when we pass an array as a parameter to a function, the entire array is copied and is available to function?
View 1 Replies View RelatedWrite 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]...
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.
I've been playing around with this piece of code:
#include <iostream>
#include <string>
#include <algorithm>
template <void(*funky)(const std::string&)>
void callback()
{funky("Hello World!");}
[Code] ....
But when I try to build it, I get this error on line 24:could not convert template argument 'lambda' to 'void (*)(const string&) {aka void (*)(const std::basic_string<char>&)}'|
I thought the lambda expression I wrote would decay to a function pointer matching the template parameter. I can guess that the constexpr qualifier might have changed the type, but without it my compiler complains that lambda needs to be declared as constexpr...
So is there a way to pass lambda expressions as template parameters?
Without having to use std::function
I have a custom struct hierarchy that goes vaguely like this:
struct Base
{};
struct Derived1 : public Base {
int num;
[Code] .....
I'm using "Base" simply as an umbrella struct, so I can access any of the derived structs with a "base" reference(&).
The issue I'm having is, I have a class that has a data member that is a reference to the struct "Base" but, I'm getting an error that says my constructor for this class doesn't provide an initialiser for that data member.
I've tried intialising a derived object for the reference, like so:
MyClass:MyClass() {
Derived1 d1;
d1.num = 0;
mBaseRef = d1;
}
But, it doesn't work...
I have a class and I would like to be able to pass an extra parameter to the function that is executed.
BigInt operator / (BigInt N,BigInt D) {
...
}
is what I have now. but I would like to do something like this. so the default value for a is 10. and if the user does something like N/D (12) Then the value of a is 12.
BigInt operator / (BigInt N,BigInt D, int a=10) {
...
}
Here is my issue: I am making a simple audioplayer in Xamarin.android but i want every time i change the track to make a crossfade effect. So im using 2 mediaplayers at the same time for the fade. The problem is that im defining one time the players and i pass the player as a parameter like this:
public MediaPlayer player = null;
public MediaPlayer player2 = null;
....
If i have to fadeout the player and start the next one im doing it like this:
if (player != null){
if (player.IsPlaying) {
cts = new CancellationTokenSource();
token = cts.Token;
FadeOut (player, 2000 ,token);
[Code] .....
So my problmem is that player and player2 remain always null. Why? i guess c# creates a copy of player and player2 and use this one. How i can pass a mediaplayer as parameter and always use only player and player2?
I've was trying out a function template to automatically get the type of a lambda, but it seems that it won't compile
I've tried two different ways:
1.
template<class HASHER>
auto make_unordered_map(size_t bucketCount, HASHER const && hf)
-> unordered_map<string const, HASHER>&& {
return unordered_map<string const, int, HASHER>(bucketCount, hf);
} auto x = make_unordered_map(1, [](string const& key)->size_t { return key[0]; });
2.
template<class HASHER>
auto make_unordered_map(size_t bucketCount, HASHER const && hf2)
-> unordered_map<string const, int, decltype(hf2)> {
return unordered_map<string const, int, decltype(hf2)>(bucketCount, hf2);
} auto x = make_unordered_map(1, [](string const& key)->size_t { return key[0]; });
The test code are located here:
1. [URL] ....
2. [URL] ....
They are both based on the code that is stated to work in those examples. I.e.:
auto hf = [](string const& key)->size_t { return key[0]; };
unordered_map<string const, int, decltype(hf)> m (1, hf);
I have in my main(), a function that creates my arg object using boost/program_options.hpp i want to pass this object to another function using templates like this:
Code:
template <typename Targ>
void Count(Targ & arg){
MyObj<string> QueryTab(arg["input-file"].as<string>()); //line number is 352
...
}
However I get an error:
Code:
../include/Filter.hpp: In member function ‘void Count(Targ&)’:
../include/Filter.hpp:352:40: error: expected primary-expression before ‘>’ token
../include/Filter.hpp:352:42: error: expected primary-expression before ‘)’ token
... obviously it does not recognize my intention, what did I do wrong?
Why wouldn't this code compile when adding '<double>' after the function call?
template<class T>
T add(T& a, T& b){
return a + b;
}
int main() {
int a, b;
cin >> a >> b;
cout << add<double>(a,b);
}
Compiler error:
cannot convert 'a' (type 'int') to type 'double&'
I make a class (it stands for an ARMA time series), and I have a method wich modifies some of its variables. In other part of my program I have a function wich receives one object of this class as a parameter and, at some point, it calls the method of the ARMA class to modify it; here is my deal I want to pass the ARMA class by reference to this function, because I want the variables of the instance I'm passing to be modified, not those of a copy the method uses. Also, I would like not to declare the function inside the class ARMA, cause I use it in other places too (it's basically a Nelder-Mead optimization what it performs).
Here is a code wich sketches what I've been trying, and exactly the error message I get is "modifyParameter has not been declared".
#include <iostream>
#include <cstdlib>
using namespace std;
class ARMA{
[code]....
How can I pass a matrix as a reference parameter? I am using the following declarations:
Code:
typedef std::vector< std::vector<std::string> > ss_matrix_t;
I declare the matrix with the following statement, where nRows and nCols are integers
Code:
std::vector< std::vector<std::string> > vI2Matrix(nRows, std::vector<std::string>(nCols,""));
The function is called with:
Code:
int read_files(std::string fname, int nCols, int nRows, ss_matrix_t &ssMat )
But I get a linker error:
error LNK2019: unresolved external symbol "int __cdecl read_splayed_files(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,int,int,class std::vector<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class std::allocator<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > > >,class std::vector<class std::vector<class
[Code] ....
I suspect the syntax of the declaration, but I am not sure what to do here? If I change the call to the function, then the array ( matrix ) is passed by value, and it takes forever:
Code:
int read_files(std::string fname, int nCols, int nRows, ss_matrix_t ssMat )
// this takes ages ( it does compile and link )