C++ :: How To Use Templated Varadic Sequences And Integral Sequence Wrappers
Jul 15, 2013
I've been studying the heck out of the boost metafunction libraries. I understand a good deal of what things like varadic functions and integral sequence wrappers are, but I am having a hard time putting everything together to get working functions, such as performing arithmetic operations or functions like that of std::vector.
Here is an example of what I'm talking about:
// Sequences
template<typename T... N> struct seq;
template<typename T, T... N> struct seq_c;
// Integral constant wrapper
template<int T> struct int_
[Code] .....
My knowledge of all of this is pretty scattered and I've really been trying hard to put it all together. Is this correct? How can I apply this and use it to do more?
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Oct 23, 2013
I would like to define a templated class while implementing default value on templated arguments. I don't know how to do that with string templated variables.
For exemple:
Code:
template <class T>
class A {
public:
A() { version = ???? }
std::string_base<T> version;
};
I don't want to pass the default value as parameter of the constructor. how I can do this?
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Oct 25, 2013
I'm trying to understand winsock with c++. Let's assume I have a 2 working applications, one is the client and one the server:
Client: I can enter a command, for example chat or filetransfer, it will then switch into this specific mode where I can enter commands like uploading a file, send a message etc.
Client
Code: ....
while (rc != SOCKET_ERROR) {
printf("
#");
gets(buf);
if (strcmp(buf, "CHAT") == 0){
// start chat mode
[Code] .....
I'm in a recv/send loop and I'm using streams...so basically all the data is being sent/received there. Now, if I want to upload a file, I send a FILETRANSFER String to the server. Then I will probably need another loop that receives file requests from the client. The server will need more details about the file, like the path, name, size...
Now, my question is, what's the best practise for something like that? I'm having problems understand how I can send 3 different values from the server to the client and how he will receive them in the right order store them in variables. And also, after sending something to the server, in some cases, the client will have to wait for the server to answer.
Is there a good example of a similar application?
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Apr 1, 2014
According to [URL] ....
" char myword[] = { 'H', 'e', 'l', 'l', 'o', ' ' };
char myword[] = "Hello";
In both cases, the array of characters myword is declared with a size of 6 elements of type char: the 5 characters that compose the word "Hello", plus a final null character (' '), which specifies the end of the sequence and that, in the second case, when using double quotes (") it is appended automatically."
However there are examples where word array is declared as :
char myword[] = { 'H', 'e', 'l', 'l', 'o' };
Is syntactically correct?? If yes, what is the size of myword? and does ' ' append by compiler automatically?
And is char myword[] = "abc" same as char myword[] = {'a','b','c',' '} or is it same as char myword[] = {'a','b','c'} ??
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Feb 4, 2015
I need to take an unknown amount of sorted files and then output any number that is in at least half of them... I know I need to read in the files to a vector and then iterate through them all at the same time looking at the lowest number first and so on. But I am stuck at the point of taking an unknown amount of files and putting them in a container.
This is what I have so far but the vector isn't working and I think I should be putting each file into its own vector.
string get_file(string filename)
{
ifstream in(filename);
if (in)
[Code]....
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Oct 6, 2014
I am very new to programming and would like to know where to even start when evaluating a double integral. I wanted to evaluate this double integral: 6x^3 + y^2 +7x from 0 to 1 (for both).
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Aug 2, 2013
One of my last programs to write was to use the trapezoidal rule to approx. the definite integral defined in the program. It works, now i am looking for ways to improve this code, if there are any.
Code:
#include<stdlib.h>#include<stdio.h>
#include<math.h>
double integral (double x);
int main(void){
[Code] ....
the output is simple:
Code: ssma-imac:ENG-3211 ssma$ ./integralThe integral of x^2 Sin(x) dx from 1 to 5 is -18.953841
And yes this is a very good approximation of the actual integral.
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Feb 13, 2013
I have a function written to calculate an integral using rectangles. I get this error: 'cannot convert double to double (*) (double) in assignment'. But whenever I remove one of the doubles something is undeclared.
double rect_integral(double a, double b, int n, int f) {
double x;
double (* fx) (double);
double func_1 = 5*(pow(x,4))+3*(pow(x,2))-10*(x)+2;
double func_2 = pow(x,2)-10;
[Code] .....
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Jun 25, 2014
Basically, I am inserting data from an ODBC connection into a PostgreSql database using the COPY query, but the COPY query stops and returns this error...
Quote
ERROR: invalid byte sequence for encoding "UTF8": 0x92
CONTEXT: COPY [TableName], line 1: "189572|1-00-1202|1-|00-|1202||AP||1...
STATEMENT: COPY [TableName] FROM STDIN (DELIMITER '|', NULL '')
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Jan 16, 2014
I've been having a problem concerning the initialization of const static integral members with floating point calculations. I'll let his sample program do the explaining:
class Foo {
public :
Foo() {}
const static int samplerate = 44100;
const static unsigned short tempo = 120;
[Code].....
I know you can't initialize const static non-integral types on the same line on which they're declared, but I don't see why even an implicit cast to an integral type should be disallowed. I make my calculations using doubles, so I'm surprised that even though it should degenerate into an integer - it's still a problem for the compiler.
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Mar 19, 2013
Code:
#include <iostream>
#include <iomanip>
using namespace std;
//chose to use #define since columns/rows are a constant in the program
#define x 5
#define y 3
int main() {
//declare variables
[code]....
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Sep 6, 2014
So far I have the following code:
// Purpose: To write a program that displays the number of millimeters higher the current level the ocean level will be in
// in 5, 7, and 10 years.
# include <iostream>
# include <string>
using namespace std;
int main() {
float X = 10;
string Y="";
[Code] ....
But I get the following error message:
IntelliSense: expession must have integral or unscoped enum type
three times in a row for lines 25, 27, and 29 and I don't understand or know why?
In case the purpose does make sense here are the directions:
2.7: Ocean Levels
Assuming the ocean’s level is currently rising at about 1.5 millimeters per year, write a program that displays
•The number of millimeters higher than the current level that the ocean’s level will be in 5 years,
•The number of millimeters higher than the current level that the ocean’s level will be in 7 years,
•The number of millimeters higher than the current level that the ocean’s level will be in 10 years,
Output labels:
Each value should be on a line by itself, preceded by the a label of the form:
In X years the ocean's level will be higher by Y millimeters.
where X is the number of years (5, 7 or 10) and Y is the value you calculate.
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Sep 3, 2013
template <typename T> struct avl_tree {
T data;
int balance;
struct avl_tree <T> *Link[2];
static int (*comp)(T, T);
};
In main, I have a function like so:
int compare(int a, int b) {
return ( a - b );
}
Now how do I assign the function pointer in my avl_tree class to the compare function?
I did this:
int (avl_tree<int>::*comp)(int, int) = compare;
But I got the compiler error:
Tree_Test.cc: In function ‘int main()’:
Tree_Test.cc:27:42: error: cannot convert ‘int (*)(int, int)’ to
‘int (avl_tree<int>::*)(int, int)’ in initialization
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Oct 7, 2014
I've this variadic template class implementation:
// Predefine template delegate factory
template < typename R, typename... Args >
class brGenericDelegate ;
// C++11 template alias to announce functor definition
template < typename R, typename... Args >
using brGenericDelegateType = std::function< std::shared_ptr<R>(Args...) > ;
[code]....
This template works fine for me. Now I have to compare, if the functors of the generic templates are equals ore not. Actually I see no way to reach this aim, because I've to cast the brDelegate on each request.
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Apr 19, 2014
I'm trying to make an templated class of List and trying to make a list of Students(another class) which I made. Its not working.
Code seems to work fine for pre-defined data types but it crashes when it comes to students. I also want to run sort function on list of students.
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Mar 12, 2012
Can I determine if a templated class has a particular constructor, in my case using a string within function to which T is used?
Code:
template<class T>
void MakeObject(std::vector<T>& dataVector)
{
std::string str "con string,Joe,24";
// catch if T has string constructor
T someObject(str); // T someObject should have constructor from string
dataVector.push_back(someObject);
}
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Apr 20, 2014
I'm trying to generalize the following (working) code:
#include <iostream>
#include <string>
#include <cmath>
int foo (int num) {return num;}
int foo (double num) {return std::round (num);}
int foo (std::string str) {return str.length();}
[code]....
Template argument deduction failed, it says. And using pred_action<T> and pred_action<FIRST> only makes it worse.Do we need to use a visitor pattern or something like that?
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Feb 3, 2014
This problem just seems really strange to me because it is simple yet for some reason my class cannot pass into another class. The class PASS_OBJECT has a static array (even with 1 element this doesn't work) and when I try to pass this class (after it is initialized) I seem to lose the data inside the PASS_OBJECT. Not only that but even when I declared the class OBJECT with the type of PASS_OBJECT<int> I seem to lose the integer 99. Here's the code, note that if you comment out line 89, 92 and 93 you will notice that line 90 outputs In main 2: 99 just fine but it doesn't otherwise???
#include <iostream>
const int size = 1;
template <class T>
class PASS_OBJECT;
template <class S>
class OBJECT {
[Code] ....
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Nov 5, 2014
To generate output data, I'm printing a bunch of vector contents to files. Because the type of variable can differ between vectors, I wrote a templated printing function to print out whatever the content of the vector is. It looks like this:
template <class T>
void SomeClass::PrintVector(std::vector<T>& Values, std::string& outFile) {
std::ofstream out(outFile, std::ios::app);
[Code] ....
I added the fixed because some larger values were being printed in scientific notation. Everything works well. My test code includes 3 vectors of doubles and 3 vectors of unsigneds. All the unsigneds work well and two of the doubles work well, but the third doubles vector prints nonsense unless I disable the fixed.
The calling code is the exact same. I know the values in the vector are correct, because a) if I comment out the "fixed" flag it works, and b) one of the unsigned vectors is sorted based on the values in that double vector (after it is printed, so the sort cannot corrupt the vector print) and works perfectly.
The "nonsense" looks like chinese/weird characters, if that matters.
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Apr 16, 2012
I declared a member method to a class in its header file and implemented it in the cpp file. When I build and run the project in XCode, everything works fine. When I try to do it with a makefile, I get undefined symbols linker errors.
parser.h
Code:
#ifndef ENGINE_SCRIPT_PARSER_H
#define ENGINE_SCRIPT_PARSER_H
#include <string>
#include "variable.h"
namespace ninja_game_engine {
[Code] ....
The exact makefile looks like this:
Code:
test:
g++
Code/Engine/Modules/Timer/timer.cpp
Code/Engine/Modules/list.cpp
[Code] ....
I'm pretty sure that there is a weird namespace gotcha that I'm unaware of that LLVM (default OSX compiler) is compensating for that g++ isn't. Or maybe something weird with the optimization? I want the tests running at that level to make sure everything that is volatile is declared as such.
Rest of the code located here: [URL] ....
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Aug 19, 2013
On several occasions in my project, I need to sort elements (indeces) based on their linked values. Those values are stored in an array. This means the comparison looks like this:
bool operator()(int i, int j) { return someArray[i] > someArray[j]; }
Because this form returns often but someArray may differ, I wrapped this in a template class:
template<class T>
struct sorter {
std::vector<T>& data;
sorter(std::vector<T>& __d) : data(__d) {}
bool operator()(int i, int j) const { return data[i] > data[j]; }
};
Now, I want to use this in a different way: I want to select the K indeces with the lowest value from someArray attached to it. My idea was to build a priority_queue, push the first K elements and then compare all the next elements to PQ.top(), as such:
INDEX t(0);
for (; t < someLimit; ++t) {
pq.push(t);
if (pq.size() == K) break;
}
for (; t < someLimit; ++t) {
if (someArray[t] < someArray[pq.top()]) { pq.pop(); pq.push(t); }
}
My problem, however, is the definition / initialization of the priority_queue object. My first idea was simply std::priority_queue<INDEX> pq(sorter<VALUE>(someArray));, but calling any function on pq provides the error "expression must have class type" (?) when hovering over pq.
My second guess, std::priority_queue<INDEX, std::vector<INDEX>, sorter<VALUE>(someArray)> pq;, provides the error 'expected a ')'' when hovering over someArray.
What is the correct way to initialize this data structure?
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Feb 20, 2013
I need to create a templated doubly linked list, with an iterator class within the list class. This program is to function just like the STL list class but I only need to implement functions that I am using, My trouble is I am kind of clueless on the iterator part and the fact that the list is templated is giving me syntax grief. I have pasted the code I have done so far.
1. On the syntax implementing the list and iterator functions outside of the class
2. I am not sure when to deference the iterator in the functions, but think I have it right so far
3. For the reverse function can I copy the list into a new list in reverse then re add them to the original list overwriting the same values? I have the code I have so far there
4. For the iterator erase function, I am not sure if I am deleting the node correctly.
5. I am not sure if I need template <typename T> above the iterator functions. Does the iterator class need to be a template? Right now it is not.
// Templated doubly linked list class
#include <iostream>
using namespace std;
template <typename T>
class list {
private:
Node *head;
Node *tail;
[Code] ....
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Jan 21, 2013
I want to specialize a particular function for Integer datatype inside a class template. My XX.h will be
namespace ZZ {
template <class T>
class XX {
void doSomething(T x);
};
}
provide me XX.cpp which has template specialization for the function doSomething on Integer datatype.
I tried the following in XX.cpp
#include "XX.h"
using namespace ZZ;
template <class T>
void XX<T>::doSomething(T x) {
[Code] ...
But this code is not working.
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Mar 23, 2015
I am working on building a set of templated data structures for my own learning and have run in to an error when instantiating my templated linked list. I receive the following error:
error LNK2019: unresolved external symbol "public: __thiscall LinkedList<int>::~LinkedList<int>(void)" (??1?$LinkedList@H@@QAE@XZ) referenced in function _main
--LinkedList.h--
#ifndef LINKEDLIST_H
#define LINKEDLIST_H
template<class T>
class LinkedList {
[code]....
why I would be receiving this error?
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Jan 14, 2014
unsigned char x1, x2, x3;
size_t ix = 0;
size_t count;
std::string Input = "EFEF9E9475C8C2D938C204EAE058F2B3";
[code]....
when debug and have a watch on out i get incomplete sequence,
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Mar 6, 2013
Code:
int main()
{
int n;
int* fib;
printf("
Fibonacci test 1: enter an integer
");
scanf("%d",&n);
fib = fibonacci(n);
printf("fib(%d) = ", n);
for(int i = 0; i < n; ++i){
printf("%d ", fib[i]);
}
What should I do/write for the fibonnaci function Code: int fibonnaci(int size)
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