C++ how to initialize vector member from list of values










4















I am trying to initialize a vector member variable with an array of integers:



#include <vector>
#include <iostream>

struct A

 A(int arr) : mvec(arr)
 
 std::vector<int> mvec;
;

int main()

 A s(1,2,3);



Compilation gives me error :



$ c++ -std=c++11 try59.cpp

try59.cpp:15:12: note: candidates are:
try59.cpp:6:1: note: A::A(int*)
 A(int arr) : mvec(arr)


How can I initialize my vector using an array of integers?






c++ c++11







share|improve this question



















  • 10





    1,2,3 is not an array, it's an initialization list. int arr is not an array, it's a pointer to int

    – Piotr Skotnicki
    Nov 14 '18 at 13:13







  • 1





    Where is the size of your array?

    – Matthieu Brucher
    Nov 14 '18 at 13:14






  • 1





    How can we initialize a vector using initialization list? The vector needs to be initialized by the initialization list passed as aruments

    – Programmer
    Nov 14 '18 at 13:16







  • 2





    Can you clarify in your question if you need to initialize the vector from an array or from an initialization_list?

    – Galik
    Nov 14 '18 at 13:17







  • 1





    Sorry I was unaware of initialization_list - I was assuming it to be an array

    – Programmer
    Nov 14 '18 at 13:19















4















I am trying to initialize a vector member variable with an array of integers:



#include <vector>
#include <iostream>

struct A

 A(int arr) : mvec(arr)
 
 std::vector<int> mvec;
;

int main()

 A s(1,2,3);



Compilation gives me error :



$ c++ -std=c++11 try59.cpp

try59.cpp:15:12: note: candidates are:
try59.cpp:6:1: note: A::A(int*)
 A(int arr) : mvec(arr)


How can I initialize my vector using an array of integers?






c++ c++11







share|improve this question



















  • 10





    1,2,3 is not an array, it's an initialization list. int arr is not an array, it's a pointer to int

    – Piotr Skotnicki
    Nov 14 '18 at 13:13







  • 1





    Where is the size of your array?

    – Matthieu Brucher
    Nov 14 '18 at 13:14






  • 1





    How can we initialize a vector using initialization list? The vector needs to be initialized by the initialization list passed as aruments

    – Programmer
    Nov 14 '18 at 13:16







  • 2





    Can you clarify in your question if you need to initialize the vector from an array or from an initialization_list?

    – Galik
    Nov 14 '18 at 13:17







  • 1





    Sorry I was unaware of initialization_list - I was assuming it to be an array

    – Programmer
    Nov 14 '18 at 13:19













4












4








4








I am trying to initialize a vector member variable with an array of integers:



#include <vector>
#include <iostream>

struct A

 A(int arr) : mvec(arr)
 
 std::vector<int> mvec;
;

int main()

 A s(1,2,3);



Compilation gives me error :



$ c++ -std=c++11 try59.cpp

try59.cpp:15:12: note: candidates are:
try59.cpp:6:1: note: A::A(int*)
 A(int arr) : mvec(arr)


How can I initialize my vector using an array of integers?






c++ c++11







share|improve this question
















I am trying to initialize a vector member variable with an array of integers:



#include <vector>
#include <iostream>

struct A

 A(int arr) : mvec(arr)
 
 std::vector<int> mvec;
;

int main()

 A s(1,2,3);



Compilation gives me error :



$ c++ -std=c++11 try59.cpp

try59.cpp:15:12: note: candidates are:
try59.cpp:6:1: note: A::A(int*)
 A(int arr) : mvec(arr)


How can I initialize my vector using an array of integers?






c++ c++11




c++ c++11






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Nov 14 '18 at 14:36







Programmer

















asked Nov 14 '18 at 13:12









ProgrammerProgrammer

2,9531851103




2,9531851103







  • 10





    1,2,3 is not an array, it's an initialization list. int arr is not an array, it's a pointer to int

    – Piotr Skotnicki
    Nov 14 '18 at 13:13







  • 1





    Where is the size of your array?

    – Matthieu Brucher
    Nov 14 '18 at 13:14






  • 1





    How can we initialize a vector using initialization list? The vector needs to be initialized by the initialization list passed as aruments

    – Programmer
    Nov 14 '18 at 13:16







  • 2





    Can you clarify in your question if you need to initialize the vector from an array or from an initialization_list?

    – Galik
    Nov 14 '18 at 13:17







  • 1





    Sorry I was unaware of initialization_list - I was assuming it to be an array

    – Programmer
    Nov 14 '18 at 13:19












  • 10





    1,2,3 is not an array, it's an initialization list. int arr is not an array, it's a pointer to int

    – Piotr Skotnicki
    Nov 14 '18 at 13:13







  • 1





    Where is the size of your array?

    – Matthieu Brucher
    Nov 14 '18 at 13:14






  • 1





    How can we initialize a vector using initialization list? The vector needs to be initialized by the initialization list passed as aruments

    – Programmer
    Nov 14 '18 at 13:16







  • 2





    Can you clarify in your question if you need to initialize the vector from an array or from an initialization_list?

    – Galik
    Nov 14 '18 at 13:17







  • 1





    Sorry I was unaware of initialization_list - I was assuming it to be an array

    – Programmer
    Nov 14 '18 at 13:19







10




10





1,2,3 is not an array, it's an initialization list. int arr is not an array, it's a pointer to int

– Piotr Skotnicki
Nov 14 '18 at 13:13






1,2,3 is not an array, it's an initialization list. int arr is not an array, it's a pointer to int

– Piotr Skotnicki
Nov 14 '18 at 13:13





1




1





Where is the size of your array?

– Matthieu Brucher
Nov 14 '18 at 13:14





Where is the size of your array?

– Matthieu Brucher
Nov 14 '18 at 13:14




1




1





How can we initialize a vector using initialization list? The vector needs to be initialized by the initialization list passed as aruments

– Programmer
Nov 14 '18 at 13:16






How can we initialize a vector using initialization list? The vector needs to be initialized by the initialization list passed as aruments

– Programmer
Nov 14 '18 at 13:16





2




2





Can you clarify in your question if you need to initialize the vector from an array or from an initialization_list?

– Galik
Nov 14 '18 at 13:17






Can you clarify in your question if you need to initialize the vector from an array or from an initialization_list?

– Galik
Nov 14 '18 at 13:17





1




1





Sorry I was unaware of initialization_list - I was assuming it to be an array

– Programmer
Nov 14 '18 at 13:19





Sorry I was unaware of initialization_list - I was assuming it to be an array

– Programmer
Nov 14 '18 at 13:19












2 Answers
2






active

oldest

votes


















5














I would just use a std::initializer_list since that's what you're already passing



A(std::initializer_list<int> arr) : mvec(arr)








share|improve this answer




















  • 1





    Thanks it solves the issue - "by value" I assume it meant that remove the reference const arr?

    – Programmer
    Nov 14 '18 at 13:18






  • 1





    yes indeed, remove the const&

    – Matthieu Brucher
    Nov 14 '18 at 13:19


















4














If for some reason you really want to initialize a vector using a C-style array and not std::initializer_list, you can do it using additional level of indirection:



struct A 
 template<std::size_t n>
 A(const int (&arr)[n]) :
 A(arr, std::make_index_sequence<n>)
 

 template<std::size_t... is>
 A(const int (&arr)[sizeof...(is)], std::index_sequence<is...>) :
 mvecarr[is]...
 

 std::vector<int> mvec;
;

A a(1, 2, 3);


Edit. As François Andrieux pointed in the comment, std::vector can be initialized using a pair of iterators, so the constructor simplifies to:



template<std::size_t n>
A(const int (&arr)[n]) : mvec(arr, arr + n)


But if you were initializing, e.g., std::array instead of std::vector, index_sequence trick seems to be unavoidable.






share|improve this answer




















  • 1





    @FrançoisAndrieux, very good point, thanks!

    – Evg
    Nov 14 '18 at 13:32






  • 1





    If you were initializing a std::array, may as well take a std::array as a parameter, no?

    – StoryTeller
    Nov 14 '18 at 13:34






  • 1





    @StoryTeller, sure. But OP took C-style array, and so did I.

    – Evg
    Nov 14 '18 at 13:36










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2 Answers
2






active

oldest

votes








2 Answers
2






active

oldest

votes









active

oldest

votes






active

oldest

votes









5














I would just use a std::initializer_list since that's what you're already passing



A(std::initializer_list<int> arr) : mvec(arr)








share|improve this answer




















  • 1





    Thanks it solves the issue - "by value" I assume it meant that remove the reference const arr?

    – Programmer
    Nov 14 '18 at 13:18






  • 1





    yes indeed, remove the const&

    – Matthieu Brucher
    Nov 14 '18 at 13:19















5














I would just use a std::initializer_list since that's what you're already passing



A(std::initializer_list<int> arr) : mvec(arr)








share|improve this answer




















  • 1





    Thanks it solves the issue - "by value" I assume it meant that remove the reference const arr?

    – Programmer
    Nov 14 '18 at 13:18






  • 1





    yes indeed, remove the const&

    – Matthieu Brucher
    Nov 14 '18 at 13:19













5












5








5







I would just use a std::initializer_list since that's what you're already passing



A(std::initializer_list<int> arr) : mvec(arr)








share|improve this answer















I would just use a std::initializer_list since that's what you're already passing



A(std::initializer_list<int> arr) : mvec(arr)









share|improve this answer














share|improve this answer



share|improve this answer








edited Nov 14 '18 at 13:19

























answered Nov 14 '18 at 13:15









CoryKramerCoryKramer

74.2k1188142




74.2k1188142







  • 1





    Thanks it solves the issue - "by value" I assume it meant that remove the reference const arr?

    – Programmer
    Nov 14 '18 at 13:18






  • 1





    yes indeed, remove the const&

    – Matthieu Brucher
    Nov 14 '18 at 13:19












  • 1





    Thanks it solves the issue - "by value" I assume it meant that remove the reference const arr?

    – Programmer
    Nov 14 '18 at 13:18






  • 1





    yes indeed, remove the const&

    – Matthieu Brucher
    Nov 14 '18 at 13:19







1




1





Thanks it solves the issue - "by value" I assume it meant that remove the reference const arr?

– Programmer
Nov 14 '18 at 13:18





Thanks it solves the issue - "by value" I assume it meant that remove the reference const arr?

– Programmer
Nov 14 '18 at 13:18




1




1





yes indeed, remove the const&

– Matthieu Brucher
Nov 14 '18 at 13:19





yes indeed, remove the const&

– Matthieu Brucher
Nov 14 '18 at 13:19













4














If for some reason you really want to initialize a vector using a C-style array and not std::initializer_list, you can do it using additional level of indirection:



struct A 
 template<std::size_t n>
 A(const int (&arr)[n]) :
 A(arr, std::make_index_sequence<n>)
 

 template<std::size_t... is>
 A(const int (&arr)[sizeof...(is)], std::index_sequence<is...>) :
 mvecarr[is]...
 

 std::vector<int> mvec;
;

A a(1, 2, 3);


Edit. As François Andrieux pointed in the comment, std::vector can be initialized using a pair of iterators, so the constructor simplifies to:



template<std::size_t n>
A(const int (&arr)[n]) : mvec(arr, arr + n)


But if you were initializing, e.g., std::array instead of std::vector, index_sequence trick seems to be unavoidable.






share|improve this answer




















  • 1





    @FrançoisAndrieux, very good point, thanks!

    – Evg
    Nov 14 '18 at 13:32






  • 1





    If you were initializing a std::array, may as well take a std::array as a parameter, no?

    – StoryTeller
    Nov 14 '18 at 13:34






  • 1





    @StoryTeller, sure. But OP took C-style array, and so did I.

    – Evg
    Nov 14 '18 at 13:36















4














If for some reason you really want to initialize a vector using a C-style array and not std::initializer_list, you can do it using additional level of indirection:



struct A 
 template<std::size_t n>
 A(const int (&arr)[n]) :
 A(arr, std::make_index_sequence<n>)
 

 template<std::size_t... is>
 A(const int (&arr)[sizeof...(is)], std::index_sequence<is...>) :
 mvecarr[is]...
 

 std::vector<int> mvec;
;

A a(1, 2, 3);


Edit. As François Andrieux pointed in the comment, std::vector can be initialized using a pair of iterators, so the constructor simplifies to:



template<std::size_t n>
A(const int (&arr)[n]) : mvec(arr, arr + n)


But if you were initializing, e.g., std::array instead of std::vector, index_sequence trick seems to be unavoidable.






share|improve this answer




















  • 1





    @FrançoisAndrieux, very good point, thanks!

    – Evg
    Nov 14 '18 at 13:32






  • 1





    If you were initializing a std::array, may as well take a std::array as a parameter, no?

    – StoryTeller
    Nov 14 '18 at 13:34






  • 1





    @StoryTeller, sure. But OP took C-style array, and so did I.

    – Evg
    Nov 14 '18 at 13:36













4












4








4







If for some reason you really want to initialize a vector using a C-style array and not std::initializer_list, you can do it using additional level of indirection:



struct A 
 template<std::size_t n>
 A(const int (&arr)[n]) :
 A(arr, std::make_index_sequence<n>)
 

 template<std::size_t... is>
 A(const int (&arr)[sizeof...(is)], std::index_sequence<is...>) :
 mvecarr[is]...
 

 std::vector<int> mvec;
;

A a(1, 2, 3);


Edit. As François Andrieux pointed in the comment, std::vector can be initialized using a pair of iterators, so the constructor simplifies to:



template<std::size_t n>
A(const int (&arr)[n]) : mvec(arr, arr + n)


But if you were initializing, e.g., std::array instead of std::vector, index_sequence trick seems to be unavoidable.






share|improve this answer















If for some reason you really want to initialize a vector using a C-style array and not std::initializer_list, you can do it using additional level of indirection:



struct A 
 template<std::size_t n>
 A(const int (&arr)[n]) :
 A(arr, std::make_index_sequence<n>)
 

 template<std::size_t... is>
 A(const int (&arr)[sizeof...(is)], std::index_sequence<is...>) :
 mvecarr[is]...
 

 std::vector<int> mvec;
;

A a(1, 2, 3);


Edit. As François Andrieux pointed in the comment, std::vector can be initialized using a pair of iterators, so the constructor simplifies to:



template<std::size_t n>
A(const int (&arr)[n]) : mvec(arr, arr + n)


But if you were initializing, e.g., std::array instead of std::vector, index_sequence trick seems to be unavoidable.







share|improve this answer














share|improve this answer



share|improve this answer








edited Nov 14 '18 at 13:32

























answered Nov 14 '18 at 13:25









EvgEvg

4,00721434




4,00721434







  • 1





    @FrançoisAndrieux, very good point, thanks!

    – Evg
    Nov 14 '18 at 13:32






  • 1





    If you were initializing a std::array, may as well take a std::array as a parameter, no?

    – StoryTeller
    Nov 14 '18 at 13:34






  • 1





    @StoryTeller, sure. But OP took C-style array, and so did I.

    – Evg
    Nov 14 '18 at 13:36












  • 1





    @FrançoisAndrieux, very good point, thanks!

    – Evg
    Nov 14 '18 at 13:32






  • 1





    If you were initializing a std::array, may as well take a std::array as a parameter, no?

    – StoryTeller
    Nov 14 '18 at 13:34






  • 1





    @StoryTeller, sure. But OP took C-style array, and so did I.

    – Evg
    Nov 14 '18 at 13:36







1




1





@FrançoisAndrieux, very good point, thanks!

– Evg
Nov 14 '18 at 13:32





@FrançoisAndrieux, very good point, thanks!

– Evg
Nov 14 '18 at 13:32




1




1





If you were initializing a std::array, may as well take a std::array as a parameter, no?

– StoryTeller
Nov 14 '18 at 13:34





If you were initializing a std::array, may as well take a std::array as a parameter, no?

– StoryTeller
Nov 14 '18 at 13:34




1




1





@StoryTeller, sure. But OP took C-style array, and so did I.

– Evg
Nov 14 '18 at 13:36





@StoryTeller, sure. But OP took C-style array, and so did I.

– Evg
Nov 14 '18 at 13:36

















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