在字符串副本上执行迭代器算术的更简单方法

Question

I have a copy ( result ) of a string ( format_ ) and then I use std::find on the original string, but I cannot use iterators obtained by this on the string copy. This results in some cumbersome code. for example:

std::string result = format_;
auto it = std::find(format_.begin(), format_.end(), '%');
auto diff = it - format_.begin();
auto pos_it = result.begin() + diff;
result.insert(result.erase(pos_it, pos_it + 2), right.begin(), right.end());

Here if I attempt to use it as an iterator rather than just for math I will get segmentation fault. If two strings are identical, why cannot you "share" iterators?

Answer 1

You can not share iterators between strings (even if they are identical) because they occupy separate memory locations and iterators may use memory pointers internally to access the strings' elements directly.

As an alternative you can use index position offsets into the strings.

Perhaps something like this:

int main()
{
    std::string right = "INSERT";
    std::string format_ = "some % text";

    auto pos = format_.find('%', 0); // pos is std::string::size_type (not iterator)

    std::string result = format_;

    if(pos != std::string::npos)
        result.replace(pos, 1, right);

    std::cout << result << '\n';
}