Question

void trim(string &str)
{
    string::iterator it = str.begin();
    string::iterator end = str.end() - 1;

    // trim at the starting
    for(; it != str.end() && isspace(*it); it++)
        ;
    str.replace(str.begin(), it, "");

    // trim at the end
    for(; end >= str.begin() && isspace(*end); end--)
        ;
    str.replace(str.end(), end, ""); // i get the out_of_range exception here
}

I want to trim a string of spaces. First I trip spaces from the starting and it works fine and then I find the positions of spaces from the end and try to remove it and it throws exception.

Why?

Answer 1

Changing a string invalidates iterators into the string. One way to fix this would be to modify the string only once. Incidentally, this might also be faster:

void trim(std::string &str)
{
    std::string::size_type begin=0;
    while(begin<str.size() && isspace(str[begin]))
      ++begin;
    std::string::size_type end=str.size()-1;
    while(end>begin && isspace(str[end]))
      --end;
    str = str.substr(begin, end - begin + 1)
}