Initializing length of std::vector

[karnavor]

Hello,

I know that when writing a class declaration, if the class contains an array of fixed length, then the length of that array can be initialized in the class declaration, without having to do so in the constructor. For example :

class MyClass
{
    int my_array[100];
};

But, is it also possible to do this with an std::vector? For example :

class MyClass
{
    std::vector<int> my_vector(100);
};

Or can the length of std::vectors only be set in the class constructor?

Thanks