Why doesn't C++ require a “new” statement to initialize std::vector?

Question

/* bar.h */
class bar{
    /* standard stuff omitted */
    std::vector foo;
};

/* bar.cpp */
bar::bar(){ 
    // foo = new std::vector();         


        

Answer 1

Because foo is an object not a pointer.

std::vector    // This is an object
std::vector *  // This is a pointer to an object
                    ^^^ // Notice the extra star.

New rerturns a pointer:

new std::vector();  // returns std::vector *

PS. You vector should probably contain objects not pointers.

std::vector   foo;
...
foo.push_back(my_obj());

Otherwise you will need to manually delete all the objects in the vector when it goes out of scope (when the containing object is destroyed). ie if you want to keep pointers in your vector you should do one of the following:

// 1. Manually delete all the elements in the vector when the object is destroyed.
~bar::bar()
{
    for(std::vector::iterator loop = foo.begin(); loop != foo.end(); ++loop)
    {
        delete (*loop);
    }
}

// 2. Use a smart pointer:
std::vector >  foo;

// 3. Use a smart container for pointers
boost::ptr_vector   foo