std::vector: vec.data() or &vec[0]

Question

When you want access a std::vector as a C array you can choose from at least four different ways, as you can see in this example:

#include 
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Answer 1

data() is brand new to C++11, that's why you don't see it as often. The idea of using &vec.front() never even occurred to me, probably because I use operator[] alot more often than front() (almost never). I imagine it's the same for other people.

Answer 2

Using &vec[0] is the most common although, I agree, does look a little odd. One thing to keep in mind for the future. If your vector happens to be a vector of objects whose class overloads the operator&(), realize that this will cause strange behavior if you call &vec[0].

This will not get the starting address of the first item in the internal contiguous array of objects, it will return whatever vec[0].operator&() would return. Most if not all of the time, that's not the address you're looking for (Jedi hand wave).

A good example of this is ATL's CComPtr. It overloads operator&() so storing it in a vector can be problematic. To get around this, ATL has a CAdapt template class which can be used to hide the operator&() on CComPtr

Answer 3

Before C++11's std::array I would say that std::vector was the most common container to be used instead of the C-style array. The [] operator usually implies constant time access, (which is what std::vector is all about), and so most coders usually choose this style to reflect array-like access and behavior.

Answer 4

If you're using C++11, then using data() is definitely preferable. In particular, if the vector is empty, then using either of the other two options yields undefined behavior! If you're not using C++11, and the vector may be empty, then be sure to check that condition.

Answer 5

data() has been part of std::string for some time now so you might read-up on that. I've found the data() implementation in std::vector to be similar. I occasionally use data() to treat a std::string as an array of raw bytes.