Running for loop depending on size of string vector

Question

I have made a string vector

vector<string> actor_;

and then added elements in it using push_back.

I now want to display all of them, for which I need to run a loop according to the number of elements in the vector. For that, I need to run the following loop:

for (int i = 0; i < (int)actor_.size; i++)
{
}

but this returns the following error:

---

error C2440: 'type cast' : cannot convert from 'unsigned int (__thiscall std::vector<_Ty>::* )(void) const' to 'int'
1>        with
1>        [
1>            _Ty=std::string
1>        ]
1>        There is no context in which this conversion is possible

---

Answer 1

size is a member function; you mean:

for (unsigned int i = 0; i < actor_.size(); i++) { }

(it's a good idea to use std::size_t instead of unsigned int as well)

Answer 2

You might want to consider using an iterator rather than relying on operator[] to access the elements (as implied by you using an integral loop counter and size()). This would allow you to change the container type in the future should you so wish without having to modify your access code.

Answer 3

The most correct would be:

for (std::vector<std::string>::size_type i = 0; i < actor_.size(); ++i) {}

That's ugly. You can simplify it with a typedef.

C++0x gives us auto, but that's easy to misuse:

for (auto i = 0; i < actor_.size() ++i) {}  // WRONG

Here again, i is an int (because 0 is an int), which means we haven't solved the problem. Iterators plus auto yield something reasonable:

for (auto it = actor_.begin(); it != actor_.end(); ++it) {}

Another option would be to use std::for_each and a lambda. STL syntax almost always favors iterators over indexes.

Oh, and GMan pointed out that C++0x makes this even easier with range-based for loops:

for (auto& a : actor_) {}