C++ :: Conditionally Return Different Types In Template
Apr 10, 2014
Is there a way to use preprocessing to conditionally return different types in a template. More specifically, is there a way to use preprocessing to block out conditional parts of code for one type verse another?
Example of what I can't get to compile for anything but POD types:
template <class T>returnTypeMatching(string inputName,string typeName) {
if(typeName="string") {
cerr<<"string types matched so returning string '"<< inputName <<"'"<<endl;
return inputName;
[Code] .....
If I switch string to long, the implied conversions let it work. I'm imagining there might be some preprocessing way to hide irrelevant conditions. I mean, this code would cause an error to return a string when T=double, so I get why there is a compiler error. However, is there a way to make that part of the code get hidden in that case when the template is processed when T=double?
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Dec 17, 2012
Is there a way in either Visual Studio 2010 or g++ (any version) to see what classes it instantiates and their code? For example to see if i avoid code bloat when i explicitly instantiate a template for certain types.
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Oct 23, 2013
I am writing a program in C. The following is an extract from my code:
Code:
enum coin_types{
FIVE_CENTS=5,
TEN_CENTS=10,
TWENTY_CENTS=20,
FIFTY_CENTS=50,
ONE_DOLLAR=100,
TWO_DOLLARS=200
[Code] .....
I'm getting the following errors:
For: new = new_coins_data_line(line);
"Incompatible types in assignment"
For: return newdata;
"Incompatible types in return"
There seem to be problems with my variables and perhaps it is related to the type 'struct coin' which has an enumerated type within it.
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Feb 9, 2012
I am interested in exploring covariant return types, but my attempt to implement them via CRTP is not working. How to accomplish what I am attempting.
Let's take a virtual clone() method as an example.
Code:
class Base {
virtual Base* clone() const = 0;
};
template <typename Derived>
class Base_CRTP: public Base {
[Code] .....
This setup is giving me :
file.cpp: error C2555: 'Base_CRTP<Derived>::clone': overriding virtual function return type differs and is not covariant from 'Base::clone'
It makes sense that even though Derived actually *is* a direct descendant of Base, this might not be recognized because Derived is a template argument. But is there any easy way around this that doesn't require using a different function name or duplicating the clone() logic in every derived class?
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Nov 16, 2014
I was creating a template and I realized that certain data-types/structs/classes would not be applicable to my template.This would cause bugs and errors if used incorrectly. Is there a way to restrict a template-capture to certain types/classes?
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May 15, 2013
I want to write a template that combines two type of resources:
class someClasses {
typedef someType ElementType;
} template<class T1,class T2>
class combo {
...
}
And I want to specify my T1 and T2 has the same ElementType, how can I write my combo class to partial specialize the general case so the ElementType check is at compile time?
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Dec 2, 2014
is it possible to define as template the following get functions.
class Config {
public:
enum { NO_ID = 999 };
struct ValueType {
bool a;
size_t b;
std::time_t c;
[code]....
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Jul 27, 2012
Is this really the preferred way to get the return type, for use in a derived class, of a function defined in the template parameter?
template<class PARAMETER> class C {
protected:
typedef typeof (reinterpret_cast<PARAMETER*>(0))->function() returntype;
};
This works just fine for me, but seems inelegant.
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Dec 9, 2013
I have this code:
#include <iostream>
#include <vector>
#include <map>
#include <string>
using namespace std;
[Code]...
and it does not compile.
The error is:
test.cpp: In function ‘int main()’:
test.cpp:20:30: error: no matching function for call to ‘func1(std::vector<int>&)’
test.cpp:20:30: note: candidate is:
test.cpp:8:45: note: template<class T, class U> std::map<T, T> func1(U)
test.cpp:8:45: note: template argument deduction/substitution failed:
test.cpp:20:30: note: couldn't deduce template parameter ‘T’
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Mar 8, 2014
I have a class where a method based on the type passed I should return a value.
prototype declared in the header file:
template <typename T>int getNum() const;
Code of the cpp file:
template <typename T> int class::getNum() const{
int c = 0;
for(int i=0;i<v.size();i++)
if(typeid(*(Pro*)v.at(i)) == typeid(T)) c++;
return c;
}
To invoke the method as I do:
ostream & operator << (ostream & os, Pro & obj) {
return os << obj.getNum();
}
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Jan 22, 2014
I have this
Code:
#include<stdio.h>
#include<ctype.h>
#include<string.h>
int check_up(char string[]);
int check_low(char string[]);
void to_up(char string[]);
void to_low(char string[]);
[Code] .....
When I compile this I have the following problems: warning: data definition has no type or storage class [enabled by default] in 'to_up(word)'conflicting types in 'to_up' function and to_low function warning: data definition has no type or storage class [enabled by default] into_up function error: unknown type name "word" in line 'printf("All uppercase %s. ", word):;'warning: parameter names (without types) in function declaration [enabled by default] in 'to_up(word)'and 'to_low(word)' 'note: previous declaration of "to_up" was here in function declaration of to_up function
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Dec 5, 2013
I'm trying to implement a simple template array class, but when i came into the operator< i actually have to use a template :
my code is something like :
template<typename _Type, std::size_t _Size>
class array {
public :
[Code] ......
but i am having an error of shadows template param 'class _Type' is it w/ the name conflict between the array template parameter and the function template parameter ?
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Nov 6, 2013
Error1error C2955: 'DoubleLinkedListInterface' : use of class template requires template argument listdoublelinkedlist.h10
Error2error C2244: 'DoubleLinkedList<T>::DoubleLinkedList' : unable to match function definition to an existing declaration doublelinkedlist.cpp7
Error3 .cpperror C2244: 'DoubleLinkedList<T>::~DoubleLinkedList' : unable to match function definition to an existing declaration 12
.h
#pragma once
#include "DoubleLinkedListInterface.h"
#include "Node.h"
#include <iostream>
[Code]....
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May 27, 2013
I have a generic template class with another template in one of its types. Now I want to specialize one of its methods for a particular (template) class, which leads to a compile error, however.
Here is the example:
#include <stdio.h>
template<typename Type>
class Obj1 {
public:
void ID() { printf("Object 1, size = %zu
[Code] .....
GCC ends with:
:35:27: error: type/value mismatch at argument 2 in template parameter list for ‘template<class Type, template<class> class O> class Foo’
:35:27: error: expected a class template, got ‘Obj2<Type>’
What is wrong with the specialization? Can it even be achieved and how (if so)?
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Nov 2, 2014
how I want the code to look. Only problem is it doesn't work (Line 11). I have some experience with templates but I'm not a pro.
Basically I want the "Channels<3>" to be a type that I can use to specify a Cable with similar to vector<float/int> it would be Cable<Channels<2 or 3>>.
What have I messed up with the syntax?
#include <iostream>
#include <vector>
using namespace std;
[Code].....
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Mar 14, 2014
I have a function:
template<class Iterator, class T>
void a(Iterator, Iterator, const T&);
and I want to be able to simplify calls to 'a' with calls like
a(someIteratableContainer);
instead of having to call:
a(someIteratableContainer.begin(), someIteratableContainer.end(), valueOfTheContainersElementType);
I also want to be able to generalize the function to handle any of the standard iteratable contains: array, vector, deque, whatever.
I was under the impression I could write:
template<template<class T> class U> a(U<T>& container) {
a(container.begin(), container.end(), g(T()));
}
where 'g()' returns an object of the element type. However, the compiler is claiming, no matter how I write a call to the overload, the original template is selected and/or the overload is invalid, depending on the various ways I attempt to write said overload.
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Mar 29, 2013
I'm writing some functions pertaining to binary trees. I've used recursion once before while learning quicksort but am still quite new and unfamiliar with it. And this is my first time touching a binary tree. So my question: In my addnode function, will the return root statement at the end ever return a value other than the value passed to the function?
Code:
#include <stdlib.h>
struct tnode
{
int data;
struct tnode * left;
struct tnode * right;
}
[code]....
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Jan 11, 2015
From the page: [URL] ....
#include <iostream>
using namespace std;
int n;
int& test();
[Code] ....
Explanation
In program above, the return type of function test() is int&. Hence this function returns by reference. The return statement is return n; but unlike return by value. This statement doesn't return value of n, instead it returns variable n itself.
Then the variable n is assigned to the left side of code test() = 5; and value of n is displayed.
I don't quite understand the bold sentence. Shouldn't value of n and variable n be the same?
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Nov 17, 2013
[URL]
#include <iostream>
struct Outer {
template<typename T>
void go() {
std::cout << Test<T>::f() << std::endl;
[Code] .....
I have tried several variants on this code to no avail. Outer is in a header, along with the extern template statements, and the specializations after main are in their own cpp file. Main is in a different cpp file.
What do have to do to make this work? I cannot bring the definitions of f() into the header, and they will be different for different template parameters. Ideally, I want Test to remain a private member of Outer, though this can change if it's the only option.
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Dec 11, 2014
I have been trying to get a hang on templates. I have the two following functions that that could be consolidated in a single template function:
void Attractor::updateFamilies(FamiliesController *_tmp, int _counter){
center.x = ofGetWidth()/2;
center.y = ofGetHeight()/3;
attractorCounter = _counter;
if(attractorCounter == 1){
[Code] .....
NotesController and FamiliesController have the same parent. The thing that I'm trying to grasp with templates is that is could something like:
template<class TYPE>
void Attractor::updateData(TYPE* *_tmp, int _counter){
center.x = ofGetWidth()/2;
center.y = ofGetHeight()/3;
attractorCounter = _counter;
[Code] ....
And then have another template function declaration for all the attractor functions where I pass the same template value as in the first one.
As you can see, I'm calling another functions inside called attractors(_tmp). I know that one way around it could be to get rid of that function and just do all the logic inside of each if statement. Is there any way to pass the same template function parameter within a template function parameter?
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Feb 9, 2015
I have a class like this
PHP Code:
template<class X>
class A {
X m_x;
public:
X* foo();
X* bar();
//others are not related to X
};
I would like to get rid of
PHP Code: template<class X>
For class level but still use it for members. Like this
PHP Code:
class A {
X m_x;
public:
template<class X>
X* foo();
template<class X>
X* bar();
//others are not related to X
};
However, I am still stuck at
PHP Code: X m_x;
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Oct 12, 2013
Let me put it into the code snippet:
/**
This class build the singleton design pattern.
Here you have full control over construction and deconstruction of the object.
*/
template<class T>
class Singleton
[Code]....
I am getting error at the assertion points when i call to the class as follows:
osgOpenCL::Context *cxt = osgOpenCL::Singleton<osgOpenCL::Context>::getPtr();
I tried commenting assertion statements and then the debugger just exits at the point where getPtr() is called.
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Aug 29, 2014
Given:
#include <string>
template <class T>
class basic_container{
[Code] .....
is this possible:
#include "../basic_container/basic_container.hpp"
template <class T>
class container_vector{
[Code] .....
If not, what do I need to do to achieve my goal?
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Oct 17, 2013
difference between return 0 and return -1 .and exit(0) and exit(1)
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Dec 12, 2014
int* count;
count = new int(1); // what???
Is this on the heap?? do i have to delete it now?
So is 'new' on a primitive data type just a way for me to allocate primitive data types (int, char, etc.) on the heap instead of the stack?
And, out of curiosity, can you do that in Java?
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Jan 9, 2015
How to convert these data types? i have an array of bytes in unsigned char[] array, and need to convert to const void* pointer.
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