How can I get a pointer to the first element in an

问题:

I want to write data from an std::vector<char> to a socket, using the write function, which has this prototype:

ssize_t write(int, const void *, size_t);

The second argument to this function must be a pointer to the first element in the std::vector<char>. How can I get a pointer to this element?

I tried std::vector::front but this returns a reference, while I need a pointer.

回答1:

&mv_vec[0]

or

&my_vec.front()

回答2:

C++11 has vec.data() which has the benefit that the call is valid even if the vector is empty.

回答3:

my_vec.empty() ? 0 : &my_vec.front()

If you would like an std::out_of_range to be thrown if vector is empty, you could use

&my_vec.at(0)

回答4:

&*my_vec.begin()

or

&mv_vec[0]

回答5:

By taking the address of the first element, with &vec[0], as the standard (since C++03, I think) demands continous storage of std::vector elements.