arr 本身的类型为 std :: string [4] .传递给函数时，它已衰减指向第一个元素的指针.在表达式 arr + sizeof(arr)/sizeof(std :: string)中， arr 的首次出现再次被衰减.第二个不是.因此， sizeof(arr)/sizeof(std :: string)的计算结果为 4 ，这是数组范围.然后，整个表达式 arr + sizeof(arr)/sizeof(std :: string)会得出指向 arr 中最后一个元素之后位置的指针.这通常称为场外迭代器.这有效地调用了构造函数 vector(首先是InputIterator，最后是InputIterator，...)，其中 InputIterator 用 std :: string * 实例化./p>

I came across a piece of C++ code in one of my projects that initializes a vector with two inputs.

One of the inputs is an existing array, and the other is the same array plus the array length.

I found a similar piece of code on another site:

// Create an array of string objects
std::string arr[] = {"first", "sec", "third", "fourth"};

// Initialize vector with a string array
std::vector<std::string> vecOfStr(arr, arr + sizeof(arr)/sizeof(std::string));

for(std::string str : vecOfStr)
    std::cout << str << std::endl;

Can someone explain what arr + sizeof(arr)/sizeof(std::string) is?

The website that this code was referenced in said that this was the corresponding constructor used:

vector (InputIterator first, InputIterator last, const allocator_type& alloc = allocator_type());

arr itself is of type std::string[4]. When passed to a function, it is decayed to pointer to the first element. In the expression arr + sizeof(arr)/sizeof(std::string), the first occurrence of arr is again decayed. The second is not. sizeof(arr)/sizeof(std::string) therefore evaluates to 4 which is the array extent. The whole expression arr + sizeof(arr)/sizeof(std::string) then evaluates to a pointer to the position past the final element in arr. This is usually called the off-the-end iterator. This effectively invokes the constructor vector(InputIterator first, InputIterator last, ...) where InputIterator is instantiated with std::string*.