Does std::vector

Question

I'm trying to reserve some spots into an std::vector, and having an error I don't understand: ``` #include #include #include using namespace std; class Foo{ public: std::string str; int i; Foo(){ this->str = ""; this->i = 0; } Foo(Foo ©Foo){ this->str = copyFoo.str; //Or get methods if private members this->i = copyFoo.i; } Foo(std::string str, int i){ this->str = str; this->i = i; } }; int main() { std::vector fooVector; fooVector.reserve(20); // Error for(int i=0; i<20; i++){ fooVector[i] = Foo("Test", i); // Or should I use operator new? // Or should I even stick to the push_back method? } return 0; } ``` Of course I could just not reserve, and it would probably work. But now I'm interested in why it is not working now. I added the copy constructor because it looked that could be the problem I was having back then. But after adding the copy constructor, it doesn't work either. The error says: In file included from /usr/local/gcc-4.8.1/include/c…

Accepted Answer

```
   std::vector<Foo> fooVector;
   fooVector.reserve(20); // Error

for(int i=0; i<20; i++){
       fooVector[i] = Foo("Test", i); // Or should I use operator new?
       // Or should I even stick to the push_back method?
   }
```

The code above is wrong. You are accessing elements beyond `size()` in the container. The idiomatic way of doing that would be doing `push_back`/`emplace_back` on the container to actually create the objects, rather than only memory:

```
   for(int i=0; i<20; i++){
       fooVector.emplace_back("Test", i);  // Alternatively 'push_back'
   }
```

Other than that, in C++11 the type used in the container requires either a copy or move constructor.

Does std::vector<Object> reserve method need a copy constructor for Object class?

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