What is the easiest way to initialize a std vector with hardcoded elements

Question

I can create an array and initialize it like this   int a      10  20  30     How do I create a std  vector and initialize it similarly elegant   The best way I know is   std  vector lt int gt  ints   ints push back 10   ints push back 20   ints push back 30     Is there a better way

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Starting with   int a      10  20  30     i m assuming a is just a placeholder   If you don t have a C  11 compiler and you don t want to use boost   const int a      10  20  30   const std  vector lt int gt  ints a a sizeof a  sizeof int      make it const if you can   If you don t have a C  11 compiler and can use boost    include  lt boost assign hpp gt  const std  vector lt int gt  ints   boost  assign  list of 10  20  30     If you do have a C  11 compiler   const std  vector lt int gt  ints    10 20 30

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If your compiler supports C  11  you can simply do   std  vector lt int gt  v    1  2  3  4     This is available in GCC as of version 4 4  Unfortunately  VC   2010 seems to be lagging behind in this respect   Alternatively  the Boost Assign library uses non-macro magic to allow the following    include  lt boost assign list of hpp gt      std  vector lt int gt  v   boost  assign  list of 1  2  3  4     Or    include  lt boost assign std vector hpp gt  using namespace boost  assign      std  vector lt int gt  v  v    1  2  3  4    But keep in mind that this has some overhead  basically  list of constructs a std  deque under the hood  so for performance-critical code you d be better off doing as Yacoby says

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Below methods can be used to initialize the vector in c      int arr      1  3  5  6   vector lt int gt  v arr  arr   sizeof arr  sizeof arr 0     vector lt int gt v  v push back 1   v push back 2   v push back 3   and so on vector lt int gt v    1  3  5  7     The third one is allowed only in C  11 onwards

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In C  0x you will be able to do it in the same way that you did with an array  but not in the current standard   With only language support you can use   int tmp       10  20  30    std  vector lt int gt   v   tmp   tmp 3          use  some  utility  to  avoid hardcoding the size here   If you can add other libraries you could try boost  assignment   vector lt int gt  v   list of 10  20  30     To avoid hardcoding the size of an array      option 1  typesafe  not a compile time constant template  lt typename T  std  size t N gt  inline std  size t size of array  T   amp   N         return N       option 2  not typesafe  compile time constant  define ARRAY SIZE x   sizeof x    sizeof x 0        option 3  typesafe  compile time constant template  lt typename T  std  size t N gt  char   amp sizeof array  T  amp   N     N         declared  undefined  define ARRAY SIZE x  sizeof sizeof array x

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If your compiler supports Variadic macros  which is true for most modern compilers   then you can use the following macro to turn vector initialization into a one-liner    define INIT VECTOR type  name         static const type name   a       VA ARGS      vector lt type gt  name name   a  name   a   sizeof name   a    sizeof  name   a     With this macro  you can define an initialized vector with code like this   INIT VECTOR int  my vector   1  2  3  4      This would create a new vector of ints named my vector with the elements 1  2  3  4

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In case you want to have it in your own class    include  lt initializer list gt  Vector lt Type gt   Vector std  initializer list lt Type gt  init list     size init list size      capacity  size    data new Type  size         int idx   0      for  auto it   init list begin    it    init list end      it           data idx       it

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If the array is    int arr      1  2  3   int len    sizeof arr  sizeof arr 0        finding length of array vector  lt  int  gt  v  std   v assign arr  arr len      assigning elements from array to vector

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If you can  use the modern C   11 14 17      way   std  vector lt int gt  vec    10 20 30     The old way of looping over a variable-length array or using sizeof   is truly terrible on the eyes and completely unnecessary in terms of mental overhead  Yuck

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you can do that using boost  assign   vector lt int gt  values    values    1 2 3 4 5 6 7 8 9    detail here

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There are a lot of good answers here  but since I independently arrived at my own before reading this  I figured I d toss mine up here anyway    Here s a method that I m using for this which will work universally across compilers and platforms  Create a struct or class as a container for your collection of objects  Define an operator overload function for  lt  lt   class MyObject   struct MyObjectList       std  list lt MyObject gt  objects      MyObjectList amp  operator lt  lt   const MyObject o                  objects push back  o            return  this             You can create functions which take your struct as a parameter  e g   someFunc  MyObjectList  amp objects     Then  you can call that function  like this  someFunc  MyObjectList    lt  lt  MyObject 1   lt  lt   MyObject 2   lt  lt   MyObject 3      That way  you can build and pass a dynamically sized collection of objects to a function in one single clean line

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There are various ways to hardcode a vector  i will share few ways    Initializing by pushing values one by one      Create an empty vector      vector lt int gt  vect         vect push back 10        vect push back 20        vect push back 30       Initializing like arrays   vector lt int gt  vect  10  20  30       Initializing from an array        int arr       10  20  30         int n   sizeof arr    sizeof arr 0          vector lt int gt  vect arr  arr   n       Initializing from another vector        vector lt int gt  vect1  10  20  30          vector lt int gt  vect2 vect1 begin    vect1 end

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I build my own solution using va arg  This solution is C  98 compliant    include  lt cstdarg gt   include  lt iostream gt   include  lt vector gt   template  lt typename T gt  std  vector lt T gt  initVector  int len           std  vector lt T gt  v    va list vl    va start vl  len     for  int i   0  i  lt  len    i      v push back va arg vl  T      va end vl     return v     int main        std  vector lt int gt  v   initVector lt int gt   7 702 422 631 834 892 104 772     for  std  vector lt int gt   const iterator it   v begin     it    v end      it      std  cout  lt  lt   it  lt  lt  std  endl    return 0      Demo

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Just thought I d toss in my  0 02   I tend to declare this   template lt  typename T  size t N  gt  std  vector lt T gt  makeVector  const T   amp data  N          return std  vector lt T gt  data  data N       in a utility header somewhere and then all that s required is   const double values       2 0  1 0  42 0  -7    std  vector lt double gt  array   makeVector values     But I can t wait for C  0x   I m stuck because my code must also compile in Visual Studio  Boo

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In C  11   include  lt vector gt  using std  vector      vector lt int gt  vec1   10  20  30       or vector lt int gt  vec2     10  20  30     Using boost list of   include  lt vector gt   include  lt boost assign list of hpp gt  using std  vector      vector lt int gt  vec   boost  assign  list of 10  20  30    Using boost assign   include  lt vector gt   include  lt boost assign std vector hpp gt  using std  vector      vector lt int gt  vec  vec    10  20  30   Conventional STL   include  lt vector gt  using std  vector      static const int arr      10 20 30   vector lt int gt  vec  arr  arr   sizeof arr    sizeof arr 0       Conventional STL with generic macros   include  lt vector gt   define ARRAY SIZE ar   sizeof ar    sizeof ar 0    define ARRAY END ar   ar   ARRAY SIZE ar   using std  vector      static const int arr      10 20 30   vector lt int gt  vec  arr  ARRAY END arr     Conventional STL with a vector initializer macro   include  lt vector gt   define INIT FROM ARRAY ar   ar  ar   sizeof ar    sizeof ar 0   using std  vector      static const int arr      10 20 30   vector lt int gt  vec INIT FROM ARRAY arr

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Before C  11    I used following methods      1  int A      10  20  30                                   original array A  unsigned sizeOfA   sizeof A  sizeof A 0                 calculate the number of elements                                                          declare vector vArrayA  std  vector lt int gt  vArrayA sizeOfA                        make room for all                                                         array A integers                                                         and initialize them to 0   for unsigned i 0  i lt sizeOfA  i        vArrayA i    A i                                    initialize vector vArrayA     2  int B      40  50  60  70                               original array B  std  vector lt int gt  vArrayB                                declare vector vArrayB for  unsigned i 0  i lt sizeof B  sizeof B 0    i        vArrayB push back B i                               initialize vArrayB    3  int C      1  2  3  4                                   original array C  std  vector lt int gt  vArrayC                                create an empty vector vArrayC vArrayC resize sizeof C  sizeof C 0                     enlarging the number of                                                          contained elements for  unsigned i 0  i lt sizeof C  sizeof C 0    i         vArrayC at i    C i                                initialize vArrayC      A Note     Above methods will work well for complex arrays    with structures as its elements

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Related  you can use the following if you want to have a vector completely ready to go in a quick statement  e g  immediately passing to another function     define VECTOR first                       static const decltype first  arr       first   VA ARGS           std  vector lt decltype first  gt  ret arr  arr   sizeof arr    sizeof  arr         return ret        example function  template lt typename T gt  void test std  vector lt T gt  amp  values        for T value   values          std  cout lt  lt value lt  lt std  endl      example use  test VECTOR 1 2f 2 3 4 5 6      though be careful about the decltype  make sure the first value is clearly what you want

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typedef std  vector lt int gt  arr   arr a  10  20  30            This would be how you initialize while defining   To compile use    clang   -std c  11 -stdlib libc     lt filename cpp gt

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In C  11   static const int a      10  20  30   vector lt int gt  vec  begin a   end a

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B  Stroustrup describes a nice way to chain operations in 16 2 10 Selfreference on page 464 in the C  11 edition of the Prog  Lang  where a function returns a reference  here modified to a vector  This way you can chain like v pb 1  pb 2  pb 3   but may be too much work for such small gains    include  lt iostream gt   include  lt vector gt   template lt typename T gt  class chain   private      std  vector lt T gt   v  public      chain amp  pb T a             v push back a           return  this             std  vector lt T gt  get     return  v         using namespace std   int main int argc  char const  argv          chain lt int gt  v         v pb 1  pb 2  pb 3        for  auto amp  i   v get              cout  lt  lt  i  lt  lt  endl             return 0         1   2   3

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If you want something on the same general order as Boost  assign without creating a dependency on Boost  the following is at least vaguely similar   template lt class T gt  class make vector       std  vector lt T gt  data  public      make vector T const  amp val             data push back val              make vector lt T gt   amp operator  T const  amp t            data push back t           return  this             operator std  vector lt T gt      return data        template lt class T gt   make vector lt T gt  makeVect T const  amp t         return make vector lt T gt  t       While I wish the syntax for using it was cleaner  it s still not particularly awful   std  vector lt int gt  x    makeVect 1   2  3  4

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A more recent duplicate question has this answer by Viktor Sehr  For me  it is compact  visually appealing  looks like you are  shoving  the values in   doesn t require c  11 or a third party module  and avoids using an extra  written  variable  Below is how I am using it with a few changes  I may switch to extending the function of vector and or va arg in the future intead      Based on answer by  quot Viktor Sehr quot  on Stack Overflow    https   stackoverflow com a 8907356    template  lt typename T gt  class mkvec   public      typedef mkvec lt T gt  my type      my type amp  operator lt  lt   const T amp  val            data  push back val           return  this            my type amp  operator lt  lt   const std  vector lt T gt  amp  inVector            this- gt data  reserve this- gt data  size     inVector size             this- gt data  insert this- gt data  end    inVector begin    inVector end             return  this            operator std  vector lt T gt    const           return data         private      std  vector lt T gt  data       std  vector lt int32 t gt     vec1  std  vector lt int32 t gt     vec2   vec1   mkvec lt int32 t gt     lt  lt  5  lt  lt  8  lt  lt  19  lt  lt  79       vec1    5 8 19 79  vec2   mkvec lt int32 t gt     lt  lt  1  lt  lt  2  lt  lt  3  lt  lt  vec1  lt  lt  10  lt  lt  11  lt  lt  12       vec2    1 2 3 5 8 19 79 10 11 12

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quot How do I create an STL vector and initialize it like the above  What is the best way to do so with the minimum typing effort  quot  The easiest way to initialize a vector as you ve initialized your built-in array is using an initializer list which was introduced in C  11     Initializing a vector that holds 2 elements of type int  Initializing  std  vector lt int gt  ivec    10  20        The push back function is more of a form of assignment with the exception of course   that it doesn t obliterate the value of the object it s being called on  Assigning ivec push back 30    ivec is 3 elements in size after Assigning  labeled statement  is executed

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The easiest way to do it is   vector lt int gt  ints    10  20  30

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It is pretty convenient to create a vector inline without defining variable when writing test  for example   assert MyFunction      std  vector lt int gt  1  3  4        lt - this

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The simplest  ergonomic way  with C   11 or later   auto my ints    1 2 3

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For vector initialisation - vector lt int gt  v    10 20 30   can be done if you have C  11 compiler  Else  you can have an array of the data and then use a for loop  int array      10 20 30  for unsigned int i 0  i lt sizeof array  sizeof array 0    i           v push back array i       Apart from these  there are various other ways described above using some code  In my opinion  these ways are easy to remember and quick to write

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If you don t want to use boost  but want to enjoy syntax like  std  vector lt int gt  v  v  1 2 3 4 5    just include this chunk of code  template  lt class T gt  class vector inserter  public      std  vector lt T gt  amp  v      vector inserter std  vector lt T gt  amp  v  v v        vector inserter amp  operator  const T amp  val  v push back val  return  this      template  lt class T gt  vector inserter lt T gt  operator   std  vector lt T gt  amp  v const T amp  x       return vector inserter lt T gt  v  x

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One method would be to use the array to initialize the vector  static const int arr      16 2 77 29   vector lt int gt  vec  arr  arr   sizeof arr    sizeof arr 0

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Before C   11     Method 1    vector lt int gt  v arr  arr   sizeof arr  sizeof arr 0     vector lt int gt v    Method 2      v push back SomeValue     C   11 onward below is also possible  vector lt int gt v    1  3  5  7

[c++] What is the easiest way to initialize a std::vector with hardcoded elements?

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