How to design classes with constructor taking a std::initializer_list?
c++,c++11,vector,initializer-list
I would take the same approach that the standard took with piecewise_construct in pair or defer_lock in unique_lock: using tags on the constructor: struct n_copies_of_t { }; constexpr n_copies_of_t n_copies_of{}; template <typename T, typename A = std::allocator<T>> class vector { public: vector(std::initializer_list<T>); vector(n_copies_of_t, size_type, const T& = T(), const A&...
Why must initializer list order match member declaration order?
c++,constructor,initializer-list
The warning is trying to prevent situations where you might be relying on the wrong ordering of the data members. Say you think B is initialized before A, and then you do something like this: myClass::myClass() : B(42), A(B) {} Here, you have undefined behaviour because you are reading from...
initializer list constructor error with CRTP
c++,c++11,initializer-list,crtp
Aggregate-initialization requires your type to be an aggregate. An aggregate cannot have base classes: An aggregate is an array or a class (Clause 9) with no user-provided constructors (12.1), no private or protected non-static data members (Clause 11), no base classes (Clause 10), and no virtual functions (10.3). ...
Implicit use of initializer_list
Your program is not ill-formed because <vector> is guaranteed to include <initializer_list> (the same is true for all standard library containers) §23.3.1 [sequences.general] Header <vector> synopsis #include <initializer_list> ... Searching the standard for #include <initializer_list> reveals the header is included along with the following headers <utility> <string> <array> <deque> <forward_list>...
Visual Studio std::array initializer bug (2797)
In this particular case you can just add a pair of parentheses: vec(Args&&... args) : v({{args...}}) {} This works with VS2013 which, I suppose, you are using. With VS2015 the code works without modifications. Also note that for C++ conformance vec2 should be rewritten as vec2(T x, T y) :...
Check whether an element is in std::initializer_list
c++,c++11,boost,initializer-list
Since a std::set's count only returns 1 or 0 you could just use that: if(set<int>{4, 8, 15, 16, 23, 42}.count(x)) Keep in mind that bare numbers can be confusing for your audience (and cause 5 seasons of Lost.) I'd recommend declaring your numbers as const and giving them a meaningful...
Is this code valid or not? GCC and Clang disagree
c++11,gcc,clang,initializer-list
Using GCC 4.9.1 and the following options: -Wall -Wextra -std=c++11 -pedantic this is what you get: prog.cc:7:5: warning: ISO C++ prohibits anonymous structs [-Wpedantic] }; ^ prog.cc: In constructor 'Bar::Bar()': prog.cc:11:21: warning: ISO C++ does not allow C99 designated initializers [-Wpedantic] Bar(void) : test{.a = 1, .b = 2} {...
Enable default initializer list constructor
c++,c++11,inheritance,initializer-list,list-initialization
Your original case relied upon aggregate initialization [dcl.init.list]: List-initialization of an object or reference of type T is defined as follows: ... — Otherwise, if T is an aggregate, aggregate initialization is performed Where an aggregate and aggregate initialiazation are, from [dcl.init.aggr], emphasis mine: An aggregate is an array or...
Why does {1, 2} has no a type, but decltype(a) is well-formed?
decltype({1, 2}) is illegal, however, the type of a has already been deduced. From the closest draft to the C++11 standard, N3337: §7.1.6.4/6 Once the type of a declarator-id has been determined according to 8.3, the type of the declared variable using the declarator-id is determined from the type of...
Initializing fixed number of variables with an initializer list
the best I could come up with when using std::initialiser_list struct Pixel { Pixel(std::initializer_list<uint8_t> rgba) : _rgba { rgba } { switch(_rgba.size()) { case 0: _rgba.push_back(0); case 1: _rgba.push_back(0); case 2: _rgba.push_back(0); case 3: _rgba.push_back(0); case 4: break; default: throw std::invalid_argument { "" }; } } std::vector<uint8_t> _rgba; }; ......
Why isn't `std::initializer_list` defined as a literal type?
c++,language-lawyer,c++14,initializer-list,constexpr
The standard committee seems to intend on initializer_list being a literal type. However, it doesn't look like it's an explicit requirement, and seems to be a bug in the standard. From § 3.9.10.5: A type is a literal type if it is: - a class type (Clause 9) that has...
Initializer list of variables
auto ar = wrap({a,b,c}); This create a temporary array of type int[3], then binds an initializer_list<int> to that array, then calls wrap which creates an array<const int> that refers to the array. At the end of the expression the array is destroyed, leaving the array<const int> with a dangling...
Why scalar in braces are not interpeted as initializer_list
c++,language-lawyer,initializer-list
First, something very important: You have two different kinds of constructors. The first in particular, C(std::initializer_list<int>), is called an initializer-list constructor. The second is just a normal user-defined constructor. [dcl.init.list]/p2 A constructor is an initializer-list constructor if its first parameter is of type std::initializer_list<E> or reference to possibly cv-qualified std::initializer_list<E>...
Cannot convert from 'initializer-list' to 'std::initializer_list &'
c++,visual-studio-2013,initializer-list
You are trying to bind a temporary to a non-const reference; std::initializer_list<Keyword>& lis Try either; std::initializer_list<Keyword> const& lis Or std::initializer_list<Keyword> lis When building with GCC, enable -Wall -pedantic it should give you an error then as well....
initializer_list and argument-dependent lookup
c++,c++11,initializer-list,argument-dependent-lookup
I believe that the problem is that the subexpression1 { a, a } does not really have a type, and as such it does not have associated types or namespaces which in turn means that ADL does not kick in. If you have a function in the global namespace, normal...
Initialization of const reference member in initializer list
c++,gcc,reference,initialization,initializer-list
GCC is correct in its interpretation of {}. [dcl.init.list]/p3.8-9 (quoting N4296; earlier drafts has the same relative ordering of these two bullets): List-initialization of an object or reference of type T is defined as follows: [7 inapplicable bullets omitted] Otherwise, if T is a reference type, a prvalue temporary of...
How do I pass a list of values to a function expecting an array?
c++,arrays,visual-studio-2012,initializer-list
Here's a very simple and flexible way: #include <iostream> template<typename T> void WriteValue(const T& arr) { for(auto c : arr) std::cout << c << std::endl; } int main() { int a = 0; int b = 1; int c = 3; WriteValue(std::array<int, 3>{a,b,c}); // nicer C99 way: WriteValue((int[]){a,b,c}); return 0;...
Simple example of an initializer list
In this case, a simple constructor will work: foo(int x, int y) : x(x), y(y) {} If the class were an even simpler aggregate (which yours would be if the data members were public) then you wouldn't even need that - this style of initialisation will initialise each member of...
initializer_list immutable nature leads to excessive copying
c++,c++11,move-semantics,c++14,initializer-list
There is a recent proposal for movable initializer lists, where, in particular, the authors say: std::initializer_list was designed around 2005 (N1890) to 2007 (N2215), before move semantics matured, around 2009. At the time, it was not anticipated that copy semantics would be insufficient or even suboptimal for common value-like classes....
Using double braces e.g. Foo{{initializer list}} to resolve ambiguity
In the end I solved this problem by having my class use a variadic parameter pack rather than an initializer list. I haven't yet come across an example where you can't bypass initializer lists in this way....
How Do I Use a Variable in new[]'s Value Initialization
c++,variables,c++11,new-operator,initializer-list
You can use a variable, but you can't use a string and expect the compiler to magically split it up. const char* ip = initializer.c_str(); const char* foo = new char[4]{ip[0], ip[1], ip[2], ip[3]}; Once you have a variable length, though, this doesn't work at all. You just have to...
convert 'std::initializer_list' to 'int'
std::initializer_list<T> cannot convert to T for the same reason that T[] cannot convert to T, and vector<T> cannot convert to T: if you merely know that you have a std::initializer_list<T>, you don't know how many elements it has. std::initializer_list<int> x = { 1, 2, 3 }; is perfectly valid. If...
Why is initializer_list constructor preferred here?
c++,c++11,constructor,language-lawyer,initializer-list
§13.3.1.7 [over.match.list]/p1: When objects of non-aggregate class type T are list-initialized (8.5.4), overload resolution selects the constructor in two phases: Initially, the candidate functions are the initializer-list constructors (8.5.4) of the class T and the argument list consists of the initializer list as a single argument. If no viable initializer-list...
Is it possible to initialize a vector in C++ like in Matlab?
c++,matlab,vector,operator-overloading,initializer-list
Just use std::vector. If you must write it yourself with arrays, probably the easiest way is to first write an initializer list constructor as described in the question you linked to: Vec(unsigned size) : N(size), e(new double[size]) {} Vec(std::initializer_list<double> l) : Vec(l.size()) { std::copy(l.begin(), l.end(), e); } Then write a...
Strange values in a lambda returning initializer_list
c++,c++11,lambda,initializer-list
From: http://en.cppreference.com/w/cpp/utility/initializer_list The underlying array is not guaranteed to exist after the lifetime of the original initializer list object has ended. The storage for std::initializer_list is unspecified (i.e. it could be automatic, temporary, or static read-only memory, depending on the situation). I don't think the initializer list is copy-constructable. std::set...
In-class member initialization with an initializer list using uniform initialization syntax? [duplicate]
c++,c++11,initializer-list,uniform-initialization,in-class-initialization
Here is the responsible grammar from N3797: // after a member declaration: braced-or-equal-initializer-list: = initializer-clause braced-init-list braced-init-list: { initializer-list ,OPT } { } initializer-list: initializer-clause initializer-list, initializer-clause initializer-clause: assignment-expression braced-init-list So I'd say the first statement is correct and it is indeed accepted by a recent gcc and clang....
std::make_map? uniform initialization
c++,initializer-list,stdmap,uniform-initialization,stdtuple
No, you cannot just call make_tuple, since first arg in this case will be initializer_list. Specify manually. std::tuple<std::map<int,int>,int> tmm2 = std::make_tuple<std::map<int, int>>({{1,2}}, 2); Create temporary map from init list. std::tuple<std::map<int,int>,int> tmm2 = std::make_tuple(std::map<int, int>{{1,2}}, 2); ...
Can't I return a list initialization directly in C++?
You can't return an array by value, and you mustn't return a pointer to an automatic or temporary object, since it will be destroyed when the function returns, leaving the pointer invalid. Return std::array if the size is a known, small constant or std::vector otherwise....
Efficient object construction supporting empty initializer lists
c++,c++11,initializer-list,perfect-forwarding
It's not clear why adding a default constructor isn't an option for you, allowing simply S s{}: struct S { S() = default; S( S&& s ) = default; std::vector< int > member; }; If that isn't suitable you have a number of options. The most obvious is to get...
In C++ template copy assignment operator not compatible with initializer_list?
c++,templates,c++11,initializer-list
Because initializer list is a non-deduced context. From [temp.deduct.type]: The non-deduced contexts are: — [...] — A function parameter for which the associated argument is an initializer list (8.5.4) but the parameter does not have a type for which deduction from an initializer list is specified (14.8.2.1). [ Example: template<class...
Nested hash_map initilizer lists
c++,hashmap,visual-studio-2013,initializer-list
There are numerous (well, at least 3) intrusive bugs related to initializer lists and uniform initialization in MSVC2013. Update According to the comments, this particular bug was removed in VS13 Update 2. Sadly, the advice is to... stay away from many of them for now. I keep the following rule...
forwarding initializer list expressions
c++,templates,c++11,initializer-list
It's not that it can't bind to the parameter of your function it's just that the compiler is unable to detect the type of your template, this compiles: #include <vector> template <class T> void foo(T&& v) { std::vector<int>(std::forward<T>(v)); } int main() { foo(std::initializer_list<int>{1,2,3}); } ...
initializer list vs. vector
c++,c++11,vector,initialization,initializer-list
The common use of std::initializer_list is as argument to constructors of container (and similar) classes, allowing convenient initialisation of those containers from a few objects of the same type. Of course, you can use std::initializer_list otherwise and then use the same {} syntax. Since a std::initializer_list has a fixed size,...
Why are initializer lists not available when changing the allocator of std::vector?
c++,c++11,memory-alignment,initializer-list,eigen3
After studying the Eigen/StdVector include file (to be precise it is in Eigen/src/StlSupport/StdVector.h line 68 of version 3.2.1), it seems that the problem originates from a partial template specialization of the std::vector within this header file. This partial template specialization replaces the STL vector as soon as you use Eigen::aligned_allocator...
Modeling Initializer Lists in C++03
c++,templates,initializer-list,c++03
It seems clunky and not very user-friendly. Is it possible to reduce this to a single line in C++03? Since you are basically imitating std::array, just rid of the constructor: template <typename T, int N> class N_Tuple { public: T values_[N]; }; Note, in this, you have to make...
C++. Inheritance and initializing member variable has compile error
c++,inheritance,initialization,initializer-list
In SubClass(int superArg, int subArg) : subVar(subArg) { SuperClass(superArg); } compilers recognize SuperClass(superArg); as a declaration (equivalent to SuperClass superArg;), (whereas I expected a creation of a temporary SuperClass). So you have superArg declared once with int once with SuperClass. A minimal code to expose your problem: void foo(int arg)...
C++11 vector with two GLfloats as pair fail to uniform initialize
c++,c++11,stdvector,initializer-list,std-pair
First of all because std::pair doesn't have constructor that takes a std::initializer_list. Secondly because std::pair is a pair, it only have two values, not four.
Using derived class members for the initialization of the parent class
c++,initialization,derived-class,initializer-list
What you are doing as-is is undefined behavior, from [class.base.init]/14, emphasis mine: Member functions (including virtual member functions, 10.3) can be called for an object under construction. Similarly, an object under construction can be the operand of the typeid operator (5.2.8) or of a dynamic_cast (5.2.7). However, if these operations...
Merge vector and initializer_list in initialization of vector>?
c++,c++11,vector,initializer-list
One possible solution is to use a helper function that does the appending. vector<string> appendStrings(vector<string>&& s1, vector<string> const& s2) { s1.insert(s1.end(), s2.begin(), s2.end()); return s1; } And use it to initialize the variable. vector<string> suffix {{"1", "2", "3"}}; vector<vector<string>> v = {{ appendStrings({"a", "b", "c"}, suffix), {"aa", "bb"}, appendStrings({"xyz", "yzx",...
c2797 List initialization inside member initializer list or non static data member initializer not implemented
c++,visual-studio,c++11,initializer-list
Visual Studio has no implement this feature yes. Workaround can be found here You can just use const ProcessingOrder m_ProcessingOrder = ProcessingOrder { Process::TUNNEL_IP_VERSION, Process::PADDING_BYTE, Process::IP_ADDRESS_FIT_IPv6_SIZE, Process::PORT_NUMBER }; For your second case. struct Attribute_t{ SSL_CTX* const m_pContext; Socket* m_pSocket; X509* m_pCertificate; }m_Attribute; then just m_Attribute = Attribute_t{SSL_CTX_new(g_SSLChoice[version].m_pfSSLMethod()), 0, 0} ...
Typecast initializer_list
No, the conversion you are trying to perform cannot be accomplished with a cast---at least, not safely. In addition, there are only three ways to create a new std::initializer_list object: With the default constructor: std::initializer_list<unsigned char> IL; With the braced-init-list syntax: std::set<int> {1, 2, 3}; By copying another initializer list...
Nested initializer list c++
c++,constructor,initializer-list
I managed to do it with the initializer lists, here's how if anyone's interested: fifteen( std::initializer_list< std::initializer_list< size_t >> init) { int pos_i = 0; int pos_j = 0; for(auto i = init.begin(); i != init.end(); ++i ) { for(auto j = i->begin(); j!= i->end(); ++j) { table [pos_i][pos_j] =...
Inconsistent gcc diagnostic for string initialization
While: char a[5] = {'h','e','l','l','o','\0'}; is invalid. (C11, 6.7.9p2) "No initializer shall attempt to provide a value for an object not contained within the entity being initialized." This: char b[5] = "hello"; is explicitly allowed by C (emphasis mine): (C11, 6.7.9p14) "An array of character type may be initialized by...
String assignment with initializer lists
string s {"IDE"}; // Type of s is explicit - std::string auto S{"IDE"}; // Type of S is an initializer list consisting of one char const*. auto c = {"IDE"}; // Type of c is same as above. auto C {string{"IDE"}}; // Type of C is an initializer list consisting...
how to assign an array from an initializer list
You cannot assign directly to an array after its declaration. Basically your code is the same as int main() { double arr[2][2]; arr = { {1, 2}, {3, 4.5} }; // error } You have to either assign the value at declaration double arr[2][2] = { {1, 2}, {3, 4.5}...
std::initializer_list and reference types
Can a std::initializer_list contain reference types (both rvalue and lvalue)? std::initializer_list<T> doesn't hold references to its elements. It uses copy-semantics by holding its values as const objects: 18.9 Initializer List [support.initlist] An object of type initializer_list<E> provides access to an array of objects of type const E. An initializer_list...
C++ get initializer list for constructor with other parameters
You can change your constructor to just get the initializer_list with: class V { private: std::vector<int> m_list; int m_size; public: V(std::initializer_list<int> init_list): m_list(init_list.begin(), init_list.end()), m_size(m_list.size()) { } }; and construct V objects with: V v1 = {1,2}; V v2({1, 2}); You don't need the size to be input anymore thanks...
no appropriate default constructor available error with initializer list
c++,visual-c++,inheritance,constructor,initializer-list
Your b has two a objects in it: one is called ao and is a member variable, and the other is the one b is inherited from. You're already initializing ao explicitly in the initializer list, but you're not initializing b's parent. You can do this by inserting a(4,5,6), in...
Assignment of initializer list
c++,c++11,operator-overloading,initializer-list,overload-resolution
Unlike auto, where a braced-init-list is deduced as an initializer_list, template argument deduction considers it to be a non-deduced context, unless there exists a corresponding parameter of type initializer_list<T>, in which case the T can be deduced. From §14.8.2.1/1 [temp.deduct.call] (emphasis added) Template argument deduction is done by comparing each...
How to construct a vector with unique pointers
c++,c++11,unique-ptr,initializer-list,list-initialization
This make_vector is a function that takes any number of arguments, and perfect-forwards them into a vector. // get the first type in a pack, if it exists: template<class...Ts> struct first {}; template<class T, class...Ts> struct first<T,Ts...>{ using type=T; }; template<class...Ts> using first_t=typename first<Ts...>::type; // build the return type: template<class...
How to make initializer list implicitly convert to the class?
The call of the function with the initializer list will work. You should do nothing special.:) The call would not be compiled if the constructor had function specifier explicit. In this case you have to use the previous call of the function f( A{1, 3.14} ); using functional notation of...
lambda return in initializer list
c++,c++11,lambda,initializer-list
Performance-wise, it should not matter all that much. You don't copy around any Bitmap objects, and the construction of your lambda should not take any noticeable time. But for readability, I would create a static member function instead of a lambda here: class RuleNameConverter { public: RuleNameConverter(const boost::property_tree::ptree& pt); private:...
Does initialization list work for base classes?
Section § 8.5.1 of the standard defines an aggregate : An aggregate is an array or a class (Clause 9) with no user-provided constructors (12.1), no brace-or-equal-initializers for non-static data members (9.2), no private or protected non-static data members (Clause 11), no base classes (Clause 10), and no virtual functions...
C++1z handling of a == test with std::initializer_list with and w/o const in an auto function
c++,auto,c++14,initializer-list,c++1z
With the adoption of N3922 at the November 2014 committee meeting, the four initializations in the question will now deduce int rather than initializer_list<int>. The paper makes auto used in the direct-list-initialization context (i.e., auto x{/*...*/};) ill-formed unless the list contains only one element, in which case the type is...
What is the Go equivalent of C++ initializer lists?
Simply use a slice: for _, value := range []string{"foo", "bar", "baz"} { fmt.Println(value) } or alternatively an array: for _, value := range [...]string{"foo", "bar", "baz"} { fmt.Println(value) } ...
C++11 initializer list fails - but only on lists of length 2
Introduction Imagine the following declaration, and usage: struct A { A (std::initializer_list<std::string>); }; A {{"a" }}; // (A), initialization of 1 string A {{"a", "b" }}; // (B), initialization of 1 string << !! A {{"a", "b", "c"}}; // (C), initialization of 3 strings In (A) and (C), each c-style...