c++: std::vector of std::vector inside a struct

I need to create a struct that sotres a std::vector<std::vector<int>> that will contain 4 vectors of ints. I tried the declaration I usually use for vector of vectors:

struct myStruct{
   std::vector<std::vector<int>> myVector(4);
};

but, when I compile, I get this error:

myProgram.cpp:79:52: error: expected identifier before numeric constant
     std::vector<std::vector<int>> myVector(4);
                                           ^
myProgram.cpp:79:52: error: expected ‘,’ or ‘...’ before numeric constant

I tried to declare the vector in the struct and then reserve 4 elements in the main(), in the following way:

struct myStruct{
   std::vector<std::vector<int>> myVector;
};

int main(){
   myStruct s;
   s.myVector.reserve(4);
   s.myVector[0].push_back(1);
   return 0;
}

In this way it compiles without errors, but I get a segmentation violation as soon as I try to push_back.

What is the proper way to do this task? And why can't I use the first declaration to specify the size of myVector? Thank you! 🙂