I have 2 std::string. I just want to, given the input string:
How come this works:
std::string s="hello";
std::string out;
std::transform(s.begin(), s.end(), std::back_inserter(out), std::toupper);
but this doesn't (results in a program crash)?
std::string s="hello";
std::string out;
std::transform(s.begin(), s.end(), out.begin(), std::toupper);
because this works (at least on the same string:
std::string s="hello";
std::string out;
std::transform(s.begin(), s.end(), s.begin(), std::toupper);
There is no space in out
. C++ algorithms do not grow their target containers automatically. You must either make the space yourself, or use a inserter adaptor.
To make space in out
, do this:
out.resize(s.length());
[edit] Another option is to create the output string with correct size with this constructor.
std::string out(s.length(), 'X');
I'd say that the iterator returned by out.begin()
is not valid after a couple of increments for the empty string. After the first ++
it's ==out.end()
, then the behavior after the next increment is undefined.
After all this exactly what insert iterator is for.
Thats the sense of a backinserter: It inserts elements to a container. using begin(), you pass a iterator to a empty container and modify invalid iterators.
I am sorry - my edits interfered with your comments. I first posted something wrong accidentally.
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.