CODEWITHSUNDEEP
c++c++11vectorstdvector
coin cheung
coin cheung

Reputation: 1107

How could I assign values to c++ vector

I know that I can initialize a vector like this: 

vector<int> v{1,3,4,6};

However, when I define a class which contains a vector, I cannot initialize it in the position that I declare it, like this:

class C {
  public: 
    vector<int> v; 
    C();
};

Thus I need to initialize it in the construction function. The following code works, but is not clean: 

C::C() {
    v.resize(4); 
    v[0]=1; 
    v[1]=3; 
    v[2]=4; 
    v[3]=6;
}

How could I initialize it neatly and directly like vector<int> v{1,3,4,6}; rather than assign values one by one ?

Edit: Maybe I have not make my situation clear. The value of {1,3,4 6} may not be predefined values, they would depend on some logic and conditions: if(condition_a) {v[0] = 0; v[1]=3; ...} else {v[0]=4;v[0]=8;...}. Thus I have to deal with some other things to know how to initialize this vector, so I cannot use initialization list as suggested in some answers. Any advice please?

Upvotes: 3

Views: 24253

Answers (4)

Gentil-N
Gentil-N

Reputation: 124

This should work :

#include <vector>
class C {
   std::vector<int> v;
public :
   C() {
      if(...)
         v = { 0, 1, 2, 3, 4 };
      else
         v = { 5, 6, 7, 8, 9, 10, 11, 12};
      //and other statement
   }
};

Upvotes: 3

user11422223
user11422223

Reputation:

You can use an initializer list for the constructor.

Pertaining to conditional initialization as per your edited question, just initialize the vector contents to 0 and then apply whatever condition(s) you require and initialize specific values accordingly:

class C 
{
  public:
    vector<int> v;
    C() : v{0,0,0,0}
    {   if(v.size()==4) // your condition
          v[0]=1;
    }
};

Upvotes: 1

songyuanyao
songyuanyao

Reputation: 172994

You can initialize it in member initializer list like

class C{
public: 
    vector<int> v; 
    C() : v {1,3,4,6} {}
};

Or use default member initializer (since C++11) like

class C{
public: 
    vector<int> v {1,3,4,6};
    C() {}
};

Upvotes: 5

NutCracker
NutCracker

Reputation: 12273

Following would work:

C::C()
    : v{ 1, 3, 4, 6 }
{}

Note that in the code above you are passing the std::initializer_list to the std::vector's constructor.

Upvotes: 7

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