C++ :: Program - Unique Values To Use As Template Parameter
Oct 14, 2014
I'm looking for a way to generate a program-wide unique value to use as a template parameter. Generating a unique value within a translation unit is pretty easy with __LINE__, but that doesn't ensure uniqueness across translation units. I thought maybe I could use __FILE__, but that can't be used as a template parameter.
I stumbled across this page: [uRL] ....
which is exactly what I want, except that the anonymous namespace trick doesn't work on all the compilers I've tried it on. (This may be due to C++11 changing anonymous namespaces to internal linkage rather than external as they did before....that page is five years old.)
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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 25, 2013
I need to assign unique integer values to words in a dictionary that have the same alphabets, for example 'act' and 'cat' should have the same integer value. Would just adding the ascii values of the letters be sufficient?
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Dec 29, 2013
I am trying to seed a vector with 52 values ranging from 1 to 52. I already have the code written to seed the vector bu how to keep from repeating the same values from being seeded. This is for a five card stud game.
#include<iostream>
#include<cmath>
#include<cstdlib>
#include<string>
#include<vector>
#include<ctime>
using namespace std;
[Code] ....
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Aug 19, 2012
I am grabbing data from three entities and want to grab a field value in each of the entites and place it in an arraylist. What I would like to do is loop through the arraylist for all the values and do something for each value only once. If the value in the array list is repeated, I want to not do anything for it and continue till the end. Basically, I loop through all the values do something for each value and skip over the repeated value if I already did something.
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Jan 16, 2014
Unless I'm missing something, it's now possible(ish)? A little concept is below, very rough around the edges. Still though, if this is valid by standard C++, why can't we have built-in support for float / double template parameters?
#include <iostream>
#include <tuple>
template<int Numerator, int Denominator>
struct Float {
constexpr static float value()
[Code] ....
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Sep 18, 2014
I have the defined a class Seconds with a template<int,int> constructor. Unfortunately, I can't seem to get an instance. Here's the class :
class Seconds {
public :
template <int num, int den> Seconds(long int);
}
And when I try to instantiate it :
Seconds *millis = new Seconds<1,1000>(30); // template argument deduction/substitution failed:
// couldn't deduce template parameter ‘num’
Is it not the right way to call the constructor?
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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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Mar 8, 2013
I have a triple hierarchy class:
template<class T> class Singleton;
class Base;
class Sub : public Base, public Singleton<Sub>;
I' using underlying auto pointers, that's why Singleton is a template class and Sub passes itself as a template parameter. I'm developing Singleton and Base and a public API allows anyone to add their own sub classes. I actually want a real triple hierarchy like this:
template<class T> class Singleton;
class Base : public Singleton<Base>;
class Sub : public Base;
So that external developers don't have to worry about templates and complexity. The problem with this is that my implementation in Singleton will now call the constructor of Base whenever I create an instance of Sub (since the template parameter is Base).I was wondering if this could be done by pre-processor macros:
template<class T> class Singleton;
class Base : public Singleton<__CLASS_NAME__>;
class Sub : public Base;
Where __CLASS_NAME__ is the class name that will be replaced by the pre-processor. Theoretically this should be possible, since the __PRETTY_ FUNCTION__ macro actually returns the class name. The problem is that one cannot do string-manipulation to remove the function name from __PRETTY_FUNCTION__.
how I can accomplish this so that the Sub class is not aware of inheriting from a Singleton<template> class?
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Nov 20, 2013
I've been trying to create a templated class that takes a template as a parameter. I'd like to specialise this class for certain partial specializations of the template parameter but can't seem to figure out how to do it nor find anything online, (although I may be searching for the wrong thing).
As an example, say I have a class A that takes a template class with two parameters as its parameter:
template< template<class X, class Y> class Z > class A {};
I'd like to have a general version of A, for a general version of Z, but a specialisation of A for a specialisation of Z, e.g. where X is int but Y is still any type.
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Oct 6, 2013
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
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Apr 2, 2015
Is there an "easy" way to define a template with a template parameter that could resolve to "nothing".
Code:
template <typename T1, typename T2, typename T3>
struct one_to_three {
public:
T1 t1;
T2 t2;
T3 t3;
};
Now I want to be able to instantiate that in such a way that T3 and T2 (if T3 also) resolve to "nothing".
Don't point me at tuple<>, this has to be a single structure. No dummy's, nothing effectively means nothing.
so on Win32
Code:
one_to_three <int, int, int> x;
sizeof(x) == 12;
one_to_three <int, nothing, nothing> y; // whatever 'nothing' needs to be.
sizeof(y) == 4;
T1 will never be 'nothing'
T2 will only be 'nothing' if T3 also is 'nothing' (if it works with T3 not being nothing, that's fine, but it won't get used that way).
Portability is a non-issue, this only needs to work in VS (2010 and higher). The 'real' solution will need up to T10, I have a solution working with SFINAE, but it takes very very long to compile and it's getting very unwieldy if you would need to add T11.
I know it's not an ideal type approach, but it is what it is, this is a necessity due to linking with a legacy API which we don't have control over.
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Sep 19, 2014
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.
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Jun 13, 2013
void extf(int a) { }
template<typename P>
struct A {
// 1
template< void (*F)(P) >
static void call(P arg) {
[Code]...
Why it is not working? What would be a proper way to pass function pointer as a template parameter?
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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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May 30, 2013
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);
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Sep 19, 2014
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.
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Jan 26, 2014
class Program {
//Accept two input parameter and returns two out value
public static void rect(int len, int width, out int area, out int perimeter) {
area = len * width;
perimeter = 2 * (len + width);
[Code] .....
why is the static keyword required in the method signature for the rect() method. It will not compile if it is absent. why?
the same is true for this example:
class Program {
static void printvalues(params int[] passedin) {
foreach (var printthis in passedin) {
Console.WriteLine(printthis);
[Code] ....
This code won't compile without the static keyword in the printvalues() method signature. why?
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Sep 16, 2013
Write a C++ program that reads lines of text from a file using the ifstream getline() method, tokenizes the lines into words ("tokens") using strtok(), and keeps statistics on the data in the file. Your input and output file names will be supplied to your program on the command line, which you will access using argc and argv[].
You need to count the total number of words, the number of unique words, the count of each individual word, and the number of lines. Also, remember and print the longest and shortest words in the file. If there is a tie for longest or shortest word, you may resolve the tie in any consistent manner (e.g., use either the first one or the last one found, but use the same method for both longest and shortest).
You may assume the lines comprise words (contiguous lower-case letters [a-z]) separated by spaces, terminated with a period. You may ignore the possibility of other punctuation marks, including possessives or contractions, like in "Jim's house". Lines before the last one in the file will have a newline (' ') after the period. In your data files, omit the ' ' on the last line. You may assume that the lines will be no longer than 100 characters, the individual words will be no longer than 15 letters and there will be no more than 100 unique words in the file.
Read the lines from the input file, and echo-print them to the output file. After reaching end-of-file on the input file (or reading a line of length zero, which you should treat as the end of the input data), print the words with their occurrence counts, one word/count pair per line, and the collected statistics to the output file. You will also need to create other test files of your own. Also, your program must work correctly with an EMPTY input file – which has NO statistics.
Test file looks like this (exactly 4 lines, with NO NEWLINE on the last line):
the quick brown fox jumps over the lazy dog.
now is the time for all good men to come to the aid of their party.
all i want for christmas is my two front teeth.
the quick brown fox jumps over a lazy dog.
Copy and paste this into a small file for one of your tests.
Hints: Use a 2-dimensional array of char, 100 rows by 16 columns (why not 15?), to hold the unique words, and a 1-dimensional array of ints with 100 elements to hold the associated counts. For each word, scan through the occupied lines in the array for a match (use strcmp()), and if you find a match, increment the associated count, otherwise (you got past the last word), add the word to the table and set its count to 1.
The separate longest word and the shortest word need to be saved off in their own C-strings. (Why can't you just keep a pointer to them in the tokenized data?)
Remember – put NO NEWLINE at the end of the last line, or your test for end-of-file might not work correctly. (This may cause the program to read a zero-length line before seeing end-of-file.)
Here is my solution:
#include<iostream>
#include<iomanip>
#include<fstream>
using std::cout;
using std::ifstream;
using std::ofstream;
using std::endl;
using std::cin;
using std::getline;
void totalwordCount(ifstream&, ofstream&);
[Code] .....
Question: In the uniquewordCount() function, I am having trouble counting the total number of unique words and counting the number of occurrences of each word. In the shortestWord() and longestWord() function, I am having trouble printing the longest and shortest word in the file. In the countLines() function, I think I got that function correct, but it is not printing the total number of lines. Is there anything that I need to fix in those functions?
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Sep 16, 2014
I am trying to write a program that determines if a string has all unique lowercase letters. However i am unable to understand how to write the code as i am very new to C++ and my professor has given us some tasks to do and has not taught us any C++. i am familiar with the syntax but am not able to understand the tasks properly and able to complete them successfully
#include <iostream>
#include <cctype>
using namespace std;
[Code].....
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Dec 4, 2013
This is my code: [tag]
Code:
#include <iostream>
#include <string>
#include <cstring>
#include <vector>
using namespace std;
[Code] .....
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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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Apr 3, 2013
#include <iostream>
#include <cmath>
#include <string>
using namespace std;
[Code]....
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Dec 4, 2013
I am developing new project in Qt with existing MFC project . SO in MFC I have a function which uses SYSTEMTime and return CString.
example
CString getTimestampString( void )
{
SYSTEMTIME systemTime;
CString datestr;
[Code]....
PS -> I cant able to make any changes in lib_know as this library is being used by many other projects..
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Jul 2, 2013
Here's my function definition
bool validateNumber(string& text, int min = 0, int max = -1, bool useMin = true,
bool getValid = true)
The code takes the string text, and checks the make sure that the input is valid and safe to convert and use as a number. However, sometimes there is not min, and sometimes there is no max. The lack of min is done by using the parameter useMin, while the lack of max is done by max < min.
My predicament is the following call:
validateNumber(text, -2);
Now, max will be used, even though I don't want it. Ideally, I would want to do something like... int max = (min - 1), ... but that doesn't work. I also can't check to see if the parameter hasn't been changed (that I know of), because the following call would make it look like it hasn't
validateNumber(text, -2, -1);
So the question is, is there a way to do what I want, without having to add in a bool useMax parameter? Or is this my only option? I don't want to do that for simplicity, but if I have to, I have to.
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Apr 25, 2013
I have a list of numbers in an array created by a class template
Code:
#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>
using namespace std;
const int CAPACITY = 20;
template <class T>
class A
[code].....
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