问题
Given this example:
std::vector<std::string> split(const std::string& str) {
std::vector<std::string> result;
std::string curr;
for (auto c : str) {
if (c == DELIMITER) {
result.push_back(std::move(curr)); // ATTENTION HERE!
} else {
curr.push_back(c);
}
}
result.push_back(std::move(curr));
return result;
}
Can I reuse the curr std:string? This snippet seems working: after curr is moved inside
the result vector, it becomes empty. I want to be sure this is not an undefined behavior in the standard and it isn't working only because of luck.
回答1:
With a few exceptions (smart pointers, for instance), moved-from objects are left in a valid but unspecified state.
In a std::string that uses the small string optimization, for instance, if the string is small, there is no dynamic allocation, and a move is a copy. In that case it is perfectly valid for the implementation to leave the source string untouched, and not incur the extra cost of emptying the string.
回答2:
May be, this link will be useful
In short, for reuse you need to call .clear method
回答3:
From http://en.cppreference.com/w/cpp/utility/move
...all standard library functions that accept rvalue reference parameters (such as std::vector::push_back) are guaranteed to leave the moved-from argument in valid but unspecified state.
来源：https://stackoverflow.com/questions/27376623/can-you-reuse-a-moved-stdstring