Question

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Can I call functions that take an array/pointer argument using a std::vector instead?

I recently came across something like this:

class X {
    public: void foo(float* p, int elements);
};

= a method that expects an array of float values.

But in the example code this was the way they used it:

std::vector<float> bar;
bar.push_back(42);
// ...

X x;
x.foo( &bar[0], (int)bar.size() );

Now I’m wondering whether this is a safe method or just happens to work with most implementations of std::vector? (maybe this is an operator-overloading thing? I’m not yet that confident with this stuff..)

Answer 1

Yes, it’s safe.

n3337 23.3.6.1/1. In C++03 standard this is 23.2.4/1

A vector is a sequence container that supports random access iterators. In addition, it supports (amortized)
constant time insert and erase operations at the end; insert and erase in the middle take linear time. Storage
management is handled automatically, though hints can be given to improve efficiency. The elements of a
vector are stored contiguously, meaning that if v is a vector where T is some type other
than bool, then it obeys the identity &v[n] == &v[0] + n for all 0 <= n < v.size().